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The Cardiff Consumer Panel: Methodological Aspects of the Conduct of a Long-Term PanelSurveyAuthor(s): Neil Wrigley, Cliff Guy, Richard Dunn, Larry O'BrienSource: Transactions of the Institute of British Geographers, New Series, Vol. 10, No. 1 (1985),pp. 63-76
Published by: Blackwell Publishingon behalf of The Royal Geographical Society (with the Institute ofBritish Geographers)Stable URL: http://www.jstor.org/stable/622250.Accessed: 07/03/2011 00:58
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63
h e
C a r d i f f
C o n s u m e r
P a n e l
methodologic l
s p e c t s
o
t h
o n d u t
o
long term
p n e l
s u r v e y
NEIL
WRIGLEY,
Lecturern
Geography,Dept
of
Geography,
University
f
Bristol,
BristolBS8
1SS
CLIFF
GUY,
Lecturern
Town
Planning,University f
WalesInstitute
f
Science nd
Technology,
Colum
Drive,
Cardiff
CFI 3EU
RICHARD DUNN,
Lecturer
n
Geography,Dept
of
Geography,
University
f
Bristol,
BristolBS8
ISS
LARRY
O'BRIEN,
Lecturer
n
Geography, ept
of
Geography,
College f
St
Pauland St
Mary,
CheltenhamGL50
2RN
RevisedMs received October1984
ABSTRACT
Panel
surveys
can
providehigh
quality
data of
unmatchable etail.
They
are of central
mportance
or the
description
andanalysisof spatialbehaviourwhich nvolvesrecurrenthoice andmovement,and for the assessment f change n
behaviourover time.
In
this
paper
a
discussionof some
methodological
spects
of
panel
surveys
s
provided
via a
description
nd
appraisal
f the
design,
conductand
characteristicsf
the
CardiffConsumer
anel
Survey
of
1982.
The
importance
f the
database
generated
y
the Cardiff
urvey,
as
a
resource
or
geographical
esearch,
s
assessed.
KEY
WORDS:
Longitudinal/Panel
urveys,
Consumer
anel,Spatial
behaviour,
Retail
change,
Shopping
diary,
Panel
attrition,
anel
ecruitment,
ata
quality
ontrol
INTRODUCTION
Issues which concern
the
design
and
conduct
of
panel
surveys
are
generally
less well known to
geographers
than
those
which relate to cross-
sectional
questionnaire
surveys.
However,
the
infor-
mation
obtained
from
longitudinal
surveys
of
this
type
is of
central
importance
for the
description
and
analysis
of
spatial
behaviour
which involves
recurrentchoice and
movement,
and for the
assess-
ment of
change
in behaviour over
time. In
this
paper
we
discuss some
methodological
aspects
of the
conduct
of
panel
surveys
focusing
on a
recently
con-
ducted
long-term panel
survey
of
urban
shopping
behaviour in
Cardiff.
Although
a
wide
range
of
longitudinal survey
designs
are
commonly
referred to
as
panel
surveys,
in
this
paper
we
adopt
the
definition
of
panel
sur-
veys
typically
encountered
in
consumer
researchand
concentrate
upon
the richest
possible
longitudinal
design
in
which a
complete
history
of the
sequence
and
timing
of
events
is
collected. A
central
charac-
teristic of such
survey
designs
is that
they
normally
involve
continuous
monitoring
of the
process
under
study
(in
our
case
shopping
behaviour)
and,
to
achieve
this,
panel
members
are
usually
asked
to
Trans. nst. Br.Geogr.N.S. 10: 63-76 (1985) ISSN: 0020-2754
Printedn GreatBritain
8/11/2019 622250
3/15
NEIL
WRIGLEYT
AL.
record all
relevant
aspects
of their
behaviour
in some
form of
diary.
For
this reason
such
surveys
have
often
been
referred to as
diary
surveys
by
geogra-
phers
and
planners.
In
panel
surveys,
all
the usual
elements of
cross-
sectional survey design and conduct remainimport-
ant
issues
(sample design,
questionnaire
layout,
interviewer
technique,
response
and
non-response
error
identification,
and so
on)
but,
in
addition,
considerable attention must
also be
given
to
panel
recruitment,
to
the reduction of
panel
attrition,
to
panel
remuneration,
and
to the
maintenance of
data
quality
over
long
monitoring
periods.
These
are
some
of
several
methodological
issues
which are
considered
in
this
paper.
Before
doing
that,
however,
it is
important
to
preface
the
methodological
discus-
sion
by
a
consideration of the
motivations
which
lead to the
instigation
of the Cardiff
panel
survey
of
1982.
In
essence,
three
major
factors
combined to
suggest
that the
early
1980s was
an
appropriate
ime
for a
new and extensive
panel
survey
in a
British
city.
First,
during
the
previous
twenty years
there had
been
major
changes
in
the
British
grocery
retailing
industry.
The
substitution of
capital
for
labour
in
the
industry,
the
increasing
scale
of
retail
units,
the
decline
of
resale
price
maintenance,
the
growth
of
'own-brand'
rading
and the concentration of market
share
amongst
a
smallerand smallernumber
of
firms,
had
resulted in and/or
accompanied
the
rapid
growth
of
major
retail
corporations
such as
Sainsbury's,
Tesco's and Asda. The
increasing pro-
ductivity
and
healthy
(sometimes
spectacular)
growth
of
profits
of
these
firms,
even
in
periods
of
economic
recession,
had
provided
continued
(often
enthusiastic)
Stock
Market
support,
and
had
helped
to
finance
major
investment
programmes
by
the
leading
firms. In their
turn,
these
programmes,
and
a
somewhat more
liberal attitude
by
planners
to the
development of edge-of-city superstores,had trans-
formed the face
of
grocery retailing
and
significantly
altered
typical patterns
of
shopping
behaviour
for a
large
proportion
of the
population
of Britain.
Accompanying
these
changes
there had also been
a
major
shift
in the balance
of
power
in the
industry,
away from
the manufacturers
of
grocery
items
and
towards
the
rapidly expanding
retail
corporations.
Indeed,
this shift
in
power
had
progressed
so far that
the
relative
positions
of manufacturers
and retailers
had
almost
completely
reversed
from those
typical
in the
early
1960s.
By
the
early
1980s,
the
major
retail
organizations
were often in a
position
to dic-
tate the
price
levels at
which
manufacturers
supplied
items
and
to
significantly
affect the
success of the
manufacturers
leading
(and
nationally
advertized)
brands
by
their
stocking
policies.
Secondly, despite these major changes and the
rapid
increase in the
size of the market
analysis
and
store
location research
units
of
the
large
firms,
there
was
a
surprising
dearth of
up-to-date
information on
the
characteristics of
shopping
behaviour
in
the
United
Kingdom.
Most
of
the information which
was
available
tended either o be tied to the needs of
the
manufacturer ather
than
the retailer and to lack
adequate
locational
information
for
retail
analysis
and
forecasting
purposes,
or to
be
rather
dated.
Thirdly,
the
potential
benefits
to be
gained
from
the
analysis
of
panel-data
had
significantly
increased
in the late 1970s and
early
1980s. In
part
this reflec-
ted the
growth
of
computing
power
and
storage
capabilities,
so that the
very
large
amounts
of
data
which
panel
surveys
typically
generate
became
much
more
straightforward
o handle.
Perhaps
more
important,
however,
was the fact that the
analysis
of
panel
data
had become a
major
research area in the
late
1970s
across a wide
range
of
disciplines,
includ-
ing
econometrics,
sociology, marketing,
statistics
and
transportation
research,
and
some of these
developments
were
beginning
to be
applied
to
geographical problems
which involved
movement
and
repeated
choice
(Pickles
and
Davies,
1984;
Davies and
Crouchley,
1985).
The
potential
thus
existed to
develop
a
new
generation
of methods of
retail
analysis
and
forecasting
based
upon panel-
data
models of urban
shopping
behaviour
(see
Goodhardt
et
al.,
1984)
and it was felt that these
would
provide important
practical
tools
for retailers
and urban
planners.
The three factors described above
provided
the
rationale
for
a
new
and extensive consumer
panel
survey
oriented to the needs
of
geographers,
plan-
ners and retailers,and which would contain detailed
locational information
on all
aspects
of
grocery
shopping
behaviour.
It
was
hoped
that the
survey
would
provide
a
major
resource
for
understanding
the
nature
of urban
shopping
behaviour
in
Britain
n
the
1980s,
the scale
and
type
of
change
in
such
behaviour since the
1960s
and
early
1970s,
and
for
the
development
of a
new
generation
of methods
for
retail
analysis
and
forecasting.
The Cardiff
survey
was
designed
to meet these
requirements
and
was
conducted
over the
period
January
o
July
1982.
It is
believed to be the most
comprehensive panel
survey
64
8/11/2019 622250
4/15
Methodological
spects
f
theconduct
f
a
long-term
anel
urvey
of urban
shopping
behaviour
ever
carried out
in
the
United
Kingdom,
and the
data
from
the
survey
are
now
available to
all researchers
via the
ESRC
Data
Archive
at
the
University
of Essex.
In
this
paper
a
description
and critical
appraisal
of
the design, conduct and characteristicsof the Cardiff
Survey
is
presented.
It
should
be
stressed
that the
paper
does not contain
analysis
of
the
survey
data as
such
results
are
presented
elsewhere
(e.g.
Wrigley
and
Dunn, 1984a,
b,
c, 1985;
Dunn
and
Wrigley,
1984a, 1985;
Dunn et
al., 1983;
Guy,
1983, 1984;
Guy
and
O'Brien, 1983;
Wrigley
et
al.,
1984).
Instead it seeks
to answer
a
series
of
methodological
questions
which
are central
to
any
evaluation
of the
Cardiff
Consumer
Panel data
as a resource
for
geographical
research.
THE CARDIFF
SURVEY
At
the
completion
of
the Cardiff Consumer
Panel
Survey,
continuous
records
on all
aspects
of
daily
food
and
grocery shopping
had been obtained
for
454 households
over
a 24-week
period
(January
o
July
1982).
The basic
unit for these
records was
the store
visit,
and for
each visit
to an
individual
store made
by
a
panel-household,
the
following
information was
obtained:
-the
name and location of the
store,
-the
time,
day
and date of the
visit,
-mode
of
transport
to
the
store,
-shopping trip
origin,
and store 'tour'
infor-
mation
(i.e.
subsequent
destinations
on same
shopping
trip),
-a
list
of
products purchased
at
the
store,
-the brands
of certain
products
purchased,
-total
expenditure
on food and
grocery pro-
ducts at
the
store,
-total
expenditure
on
non-food/non-grocery
products
at
the
store,
-an identificationof whether the store visit was
made
by
the
panellist,
other
household mem-
ber,
or non-household
member.
In
addition,
a
wide
range
of
socio-economic,
demo-
graphic
and attitudinal
information was obtained
describing
each
panellist
and his/her
household,
plus
a
more
limited,
but
extremely
useful,
range
of
infor-
mation
on
typical
store
prices
during
the
survey
period.
The
basic information
on
each
store visit was
reduced to
one
(sometimes two)
computer-records
of
80 characters. For
the
24-week
period
this
amounts to
a
total
of
83
548
computer-records,
covering
expenditure
of more than
?4
million,
and
visits
to
over
1000
different
stores.
In
the
period
of two
years
since
the data from the
Cardiff
survey
became
available,
they
have been
used to
develop
and test
new methods of
retail
analysis and forecasting and to study the following
diverse
topics:
-patterns
of
repeat
buying
at individual stores
(Wrigley
and
Dunn, 1984a;
Dunn
et
al.,
1983);
-multi-store
purchasing patterns
and the
incidence
of store
switching
(Wrigley
and
Dunn,
1984b);
-the interaction
of
store-choice
and brand-
choice
(Wrigley
and
Dunn,
1984c);
-the
relationship
between
household
income
and
shopping
behaviour
(Guy,
1983);
-Sunday
and
late-night
shopping
(Wrigley
et
al.,
1984);
-the
degree
and
pattern
of
loyalty
to
grocery
stores
(Dunn
and
Wrigley,
1984a);
-the
nature
of
multi-stage
and
multi-purpose
shopping
journeys,
and the
identification
of
shopping
activity
bundles
(Uncles, 1985);
-the market
performance
of
particular
stores
or
store
groups
(Guy
et
al.,
1984;
Dunn and
Wrigley,
1984b);
-the
usage
of
edge-of-city
and
within-city
superstores
(Guy,
1983, 1984;
Dunn and
Wrigley,
1985);
-comparison
of the
shopping
behaviour of
women
holding
full-time,
part-time,
or no
paid
employment
(Uncles,
1984);
-comparison
of the
shopping
behaviour of
the
unemployed
and
employed
in
a
period
of
recession
(Guy,
1985);
-the
analysis
of
home-shopping,
including
mobile traders and
tele-shopping
(Uncles
and
Ducatel,
1984);
-changes
in
shopping
trip
characteristics
since
the
early
1970s
(Broom
and
Guy,
1983;
Uncles,
1985).
Furthermore,
we
expect
these studies
to
be
only
a
small
part
of
the
retailing
and consumer research
which will
be
based
on
this
data base over
the next
five to ten
years,
and a number of further
projects
are
currently
under
way
including
a
NSF-funded
cross-cultural
comparison
of
British
and American
consumer
spatial
behaviour,
using
a
slightly
modi-
fied
version
of the Cardiff
panel
survey
design
in
California
(Golledge
and
Wrigley,
1983).
In
addition,
it is
already
apparent
that
the
data
base is
being
utilized
for the
purposes
of basic model
65
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5/15
NEIL
WRIGLEY
ETAL.
TABLE
.
Characteristics
f
some
eographical/planning
onsumer
anel
urveys
Panel
Panel
Length
Study
Location
Size
(weeks)
Garrison
t
al.
(1959)
Cedar
Rapids,
USA
262
4t
Marble
Bowlby
1968)
Cedar
Rapids,
USA
116
4
Davies
1973)
Coventry,
UK
487
1
Rogers
1974)
Peterborough,
K
172
4
Hudson
1975)
Bristol,
UK
89*
10
Hanson
Hanson
1980)
Uppsala,
weden
296
5
Wrigley
1980)
Bradford,
K
102 20
O'Kelly
(1981, 1983)
Hamilton,
Canada
704
2
Daws McCulloch
(1974)
Watford,
UK
1672
1
Bruce Mann
1977)
North
London,
UK 1707
1
Bullock
t
al.
(1974)
Leicester,
K
450*
1
Guy
et al.
(1983)
Cardiff,
K
454
24
*all
panellists
were students
tmost analyses
performed
n
99 households over 2 weeks
development
and
testing
by
a number of social
scientists
(e.g.
Halperin
et
al., 1984;
Dunn and
Wrigley,
1985;
Davies
and
Pickles,
1985).
The Cardiff
survey
differs from
previous
con-
sumer
panel
surveys
in two main
respects.
First,
in
contrast
to commercial
consumer
panel
surveys
in
the
United
Kingdom
run
by
organizations
such as
Audits of Great
Britain,
Attwood
Statistics,
British
Market
Research
Bureau,
and Mass
Observation
(UK) Ltd,
it contains
detailed
locational
nformation
on consumer travel and
purchasing
behaviour
which
the
commercial
surveys
typically
do
not
collect
and/or
report.
Secondly,
compared
to
previous
con-
sumer
panel
surveys
carried
out
by
geographers
or
planners,
and which do
provide
detailed
locational
information,
it covers
a much
longer period
(six
months)
which
is of
a
similar
length
to that
encountered
in commercial
surveys.
In
contrast,
as
shown
in Table
I,
previous
geographical/planning
surveys
have
tended to be
rather restricted
in
terms
of
length
of
monitoring period
and/or
panel
size.
THE PANEL ACCOUNTING
EQUATION
To introduce
several
of the
important
issues
of
panel
survey methodology
use is
made of the
following
equation:
Number
f
recruitment
ate
/
attrition ate
households
x x
1-
sampled
100
100
Number f
Final
panel
-
non-continuous
used
for
reporters
analysis
which we
term the consumer
panel
accounting
equa-
tion. The
key
parameters
in the
equation
are the
recruitment rate and attrition rate. The
recruitment
rate
is
defined
as the
percentage
of households sam-
pled
who
agree
to become members
of the
panel.
The attrition rate
is
defined as
the
percentage
of
households
who,
having
joined
the
panel,
fail to
remain members
of it
for
the
full
monitoring
period
(24
weeks
in the Cardiff
survey).
Also,
panellists
who
leave the
panel
for some
specified length
of
time,
and thus become what
are termed 'non-
continuous
reporters',
are
usually
excluded
from
the final
panel
used for
analysis
for
reasons
of
consistency.
Fig
1
gives
a
diagrammatic
representation
of
the
process
of
obtaining
the final
panel
and
intro-
duces certain terms
used in
the
paper.
In
the
Cardiff
survey
2012 households were
sampled
using
a
multi-stage
stratified random
design.
Of
these,
775
were
not
contacted
or refused
to answer
a short
'initial'
questionnaire
(for
details
see
below).
Of
the
1237 who were contacted and who also completed
the 'initial'
questionnaire,
605
agreed
to
become
members of the
panel (representing
a recruitment
rate of 30
per
cent)
and 632
(termed
the
'non-panel-
lists')
refused.
The
group
of 605
'panellists'
represents
the
starting
size
of the
panel.
Of
these,
481 remained members
of
the
panel
for the
full
24-week
monitoring
period
and
124
dropped
out
(representing
an attrition rate
of 20
per
cent).
Those
who failed
to
remain
members of the
panel
we
term
'drop-outs'
and those who
remained we
term
'stayers'.
Finally,
the
records
of
27
'non-continuous
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Methodological
spects
f
theconduct
f
a
long-term
anel
urvey
Note :
figures
refer to the Cardiff
consumer
panel.
FIGURE .
Stages
n
the
process
of
obtaining
consumer
anel
reporters'
were
removed from the data files
leaving
a
total of 454 'continuous
reporters'
whose
purchasing
records constitute the
final
panel
data set used
for
analysis
purposes.
TARGETS AND
PILOT SURVEY
Initial
targets
and
estimates
The first
step
in
any
panel
survey
is to
specify
a
target
for
the size of
the
final
panel.
In the Cardiff
survey
the
target
was
a
panel
in the
range
450-500
households
providing
continuous records of
grocery
purchasing
over
24
weeks. The
number of house-
holds which must
be
sampled
to meet such a
target
depends upon
three
criticalfactors:
1
the
assumed recruitment
rate;
2 the
assumed attrition
rate;
3 the
likely
number of
'non-continuous
reporters'.
Closely
related to
these three factors
are the
questions:
a
how best to
design
a
'diary'
within which
infor-
mation on
purchasing
behaviour
will be
recorded;
b how best to administer the survey to maintain
the
quality
of the
data.
The first
estimates
of recruitment
rate
and
attrition
rate for the
Cardiff
survey
were 58
per
cent
and 30
per
cent
respectively.
These
figures
were
based
upon
consultation
with
appropriate
com-
mercial
firms and
comparison
with
previous
surveys.
However,
because the nature of
the Cardiff
survey
was
significantly
different
from
previous
studies,
a
detailed
12-week
pilot
survey
was undertaken to
test
these
assumptions.
The
pilot
survey
was
also
extremely
valuable in
improving
the
layout
of the
diary
in which
the
panellists
recorded
the
infor-
mation on their
purchasing
behaviour,and in
testing
the
survey
administration and data
quality
control
procedures.
Overall,
the
importance
of this
pilot
sur-
vey
cannot be
overstressed
and some brief
details
are
necessary
(Wrigley
and
Guy,
1981).
Pilot
survey
In the
pilot
survey
90
randomly
selected
households
in
two sub-areas of
Cardiffwere
sampled,
and a
32
per
cent
panel
recruitment rate was
achieved. In
terms
of
Fig
1,
there
were
29
panellists,
47
non-panellists,
and 14
non-contacts or
refusals
to
answer the 'initial'
questionnaire.
The
pilot
survey
thus
had a
substantially
lower
recruitment rate
than
originally
envisaged
and it
highlighted
the
arduous
nature of
this
stage
of
a
long-term
consumer
panel
survey.
It also
emphasized
that
in
the main
survey
the
recruitment
stage
must be
carefully
prepared
and
adequately
costed,
and should
not be
rushed
in
any
way.
The
pilot
survey
ran
for 12
weeks
(September
to
December,
1980)
during
which
time
only
three
of
the
29
panellists
dropped
out;
an
attrition rate
of
only 10 per cent. This suggested that there was little
support
for a
pessimistic
view of a
very
high
attrition rate in the main
survey,
and that
the initial
estimate of
30
per
cent for the
attrition
rate over 24
weeks was
high
rather
than
low.
On the basis of
these results
revised
estimates
of the
recruitmentand
attrition
rates
to be
expected
in
the main
survey
were
made;
these
were 38
per
cent
and 25
per
cent
respectively.
This
suggested
that
about 1800
house-
holds
needed to
be
sampled
at the
first
stage
of
the
main
survey
if
the
target
size
of the
final
panel
was
to be
achieved
successfully.
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WRIGLEYTAL.
The
pilot
survey
also
provided
an
important
opportunity
to
test
the
survey
administration,
panellist/fieldworker
control,
and
panel
remunera-
tion
procedures
to be
used
in
the
main
survey,
and
to make several
improvements
to
the
design
of the
weekly diary of grocery shopping behaviour (the
basic
data
collection device in
the
Cardiff
survey).
In
the latter
context,
particular
attention was
given
to the
layout
of
the
diary,
to
the
elimination of
any
possible
ambiguities,
and
to the elimination
of
any
response
bias which
might
be caused
by
the
adoption
of
a
particularordering
of
the list
of
product
categories
used to record
purchases.
MAIN
SURVEY: RECRUITMENT
PHASE
Sample
design
The
choice
of
Cardiff
as the location of the consumer
panel
had
been
fixed at the
outset,
largely
for
prag-
matic
reasons,
being
of suitable
size,
convenient for
both
principal
investigators,
and
offering
a suffi-
ciently
heterogeneous
range
of retail
opportunities,
housing
types
and
social sub-area
characteristics. n
addition,
it also offered considerable
potential
cost
savings
associated with
the
availability
of
prior
research on
the
retail structure of
the
city,
and
because
an
experienced
commercial
market research
firm,Research and Marketing (Wales and the West)
Ltd,
which
the
principal investigators hoped
to
employ
to conduct the
survey,
was located
in
the
city
and thus could
operate
at
substantially
lower
unit
costs.
The
experience
of
previous
commercial
surveys
and
of
the
pilot
survey
indicated that considerable
advantages
were to be
gained
by
clustering
panel-
households.
This
reduced
between-panellist
journey
times
for
the
fieldworkers,
and
helped
lessen the
considerable
problems
associated with
attributing
a
unique
numerical code to each store visited
by
the
panellists.
As a
result,
panel-households
were selec-
ted from 8 sub-areas of north
and
east
Cardiff
(see
Fig
2)
via
a
multi-stage
stratified
random
design.
The 8 sub-areas included a
wide
variety
of
housing
types
within
both the
private
and
public
sectors
of the
market,
and
were
representative
of
a
range
of
locational,
accessibility
and socio-economic
conditions.
Recruitment
rocedures
On
the basis of
the
pilot
survey
results,
the
estimated recruitment
and
attrition rates
for the main
survey
indicated that
approximately
225 households
should
be
sampled
in each
sub-area
(a
total of
1800
households)
to
produce
a final
panel
size of
450-500.
In
the
event,
panel
recruitment
n
January
1982 proved to be even more arduousthanhad been
expected,
primarily
because of the worst snowfalls
for
50
years
and the
subsequent paralysis
of the
transport
system
of
the
city.
Thus,
in four sub-areas
the
number
of households
sampled
had to be
increased
slightly, leading
to the final
figure
of 2012
households
sampled
(see
Fig
1)
and
a final
recruit-
ment
rate of 30
per
cent.
The households
sampled
within each
sub-area
were
pre-selected using
a random
design,1
and three
visits were made
at different times of
day
before
a
household
was defined
as a
non-contact.
If
contact
was made with a
household,
a short interview
(termed
the 'initial
questionnaire')
was
completed,
if
possible,
with the
principal
food and
grocery
shop-
per.
This contained
a
small number
of
questions
on
the
socio-economic
and
demographic
composition,
and
shopping
habits,
of the
household.
It
served two
important purposes:
a
to
establish
the credentials of
the
fieldworker
and a
relationship
with the
respondent.
A
blunt
request
from
a
stranger
(or
by
letter)
to become
a
panellist,
without
any
prior
discussion,
would
have
almost
always
been
unsuccessful;
b
to
provide
basic
information about
panellists
and their
households,
and to allow
comparisons
to
be
made between
panellists
and those unwil-
ling
to become
panellists
(the
so-called
'non-panellists'-see
Fig
I
and discussion
below).
On
completion
of the
interview,
the
respondent
was
asked if he/she would
be
willing
to
help
with
diary
completion
'over
the next few
months'.
Those
willing
to
participate
were revisited
the
following
week,
and as
many
as
possible
were
recruited
to the
panel. At that time, the process of diary completion
was
fully
explained,
and it was
emphasized
that
a
small
payment
(?4)
would
be made
every
four
weeks
if the diaries had been
completed properly
over that
period.
Once
the
respondent
had
agreed
to
participate
he/she was
given
the first
diary,
various
notes
to
help
diary
completion,
and
a
folder
of
information
about
the
survey.
The
following
week,
all
panellists
were
revisited so that the
first
week diaries
could
be collected
and
checked,
and
arrangements
or
subsequent
fortnightly
fieldworker
visits
were
made.
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Methodological
spects
f
the
conduct
f
a
long-term
anel
urvey
Key
to
District
Centres
1
Countisbury
Avenue
2
Maelfa 3
Leo's,
Splott
4
Albany
Road
5
Crwys
Road
6
Whitchurch Road 7
Merthyr
Road
8
Cowbridge
Road
East
9Clare
Road
10
Hoel-y-deri
FIGURE
.
Location f
study
areas n
Cardiff
MAIN
SURVEY:
MONITORING
PHASE
The
'running-in'
eriod
The
standard
commercial
practice
in
long-term
con-
sumer
panel
surveys
is to
have a
'running-in'
period
before the
start
of the main
monitoring
period.
In
the
Cardiff
survey
a
two-week
'running-in'
period
was
used,
during
which
period
panellists
completed
diaries
but for
which the
information
obtained
was
not
coded
or
used
for
analysis
purposes.
This
period
allowed
the
fieldworkers
to
check
through
the
first
completed
diaries
with the
panellists
in
detail
and
to
point
out
and
correct
any idiosyncratic
recording
errors
before
such erroneous
practices
became
established.
In
addition,
these diaries
were
checked
in
detail
by
supervisory
staff
at Research
and
Marketing
Ltd so that fieldworker
deficiencies
could
also be
corrected.
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TAL.
This
'running-in'
period proved
to
be
an
immen-
sely
useful
adjustment
period
in
which initial
problems
could be
overcome,
the
composition
of
the
panel
could be
finely
tuned
(a
small number of
panellists
were also recruited
in this
period),
and
supervisory systems could be tested. It is the firm
belief of the authors that
such
periods
offer
major
benefits in
panel
surveys,
(i)
in terms of
improving
data
quality
and
panel composition,
and
(ii)
because
they
allow
the researcher to avoid
unnecessary
(and
expensive)
coding, editing
and
computer
file
creation
for the substantial
number of
panellists
who
can be
expected
to leave the
panel
within
the
'running-in' period,
often after
having
produced
low
quality
information for
just
a
few
days.
(Such
panellists
are termed 'immediate
drop-outs'
and we
compare
their
characteristics
o the
'later
drop-outs',
'stayers'
and
'non-panellists'
below).
Attrition
rate
As noted
above,
the
attrition rate in
the main
survey
was
20
per
cent
(better
than
estimated)
and
Fig
3
summarizes
the
pattern
of
panel
attrition
over
time.
This
graph
follows
the
classical
pattern
with
a
large
number of
drop-outs
in the
'running-in'
period
and
in the
early
weeks
of the
main
monitoring
period.
In
fact,
62
per
cent
of
panel
attrition
had taken
place
by
the
end
of
the first week
of the main
monitoring
period, and from the third week onwards the
average
weekly
loss was
only
1-7
panellists.
Techniques
f
attrition ontrol
The rate of attrition
achieved
in
panel
surveys
is
directly
related to the
attention devoted to
the
issues of
panel
recruitment,
panel
control,
panel
remuneration
and fieldworker
control. In the
original
design
of the Cardiff
survey
considerable
care
was devoted to
these
issues,
and
the
pilot
survey
confirmed
their
importance.
In
summary,
six
points
appear
to
be
important
if
panel
attrition is
to be
kept
to a minimum.
The
frequency
and
nature
of
visits
by
fieldworkers
to
panel
members The Cardiff
survey
adopted
a
fortnightly
pattern
of
fieldworker
visits to collect
diaries,
and
panellists
retained
the same
field-
worker
throughout
the
survey.
This
pattern
of visits
involved the use
of 15 fieldworkers
and was
expens-
ive,
but
it
was
vital to the success
of
the
survey.
Panellists soon build
up
a
relationship
with
their
fieldworkers which then
serves to
reduce
attrition
significantly.
In
addition,
fieldworkers
play
an
Running-in
I
pe,iod
,
2
4
6
8 10 12
14 16
18
20
2 24
Week
number
FIGURE. The
pattern
f
panel
attrition ver
time
important
educational role
(especially
in the
early
stages
of the
survey)
and if
they
arewell trained and
controlled
this
significantly improves
the
quality
of
the
diary
information
obtained.
The
design
and
time
span
of
the
diary
The
layout
of
the
diary
should
make it
as
easy
as
possible
for
panellists
to
supply
the
required
information,
and
in
this
respect
a number of
improvements
were
made
on the basis
of reactions
from
panellists
to the
diary
used
in
the
pilot
survey.
A
second
important
factor
was the
decision
to use
weekly
(rather
than
fortnightly
or
monthly)
diaries.
Again,
this increased
the cost
of the
survey
but it:
(i)
resulted
in a
diary
that
was
less
daunting
in
size;
(ii)
allowed
more
effective office
control,
includ-
ing
a week
by
week
checking
of
attrition
rates,
quality
of
reporting,
and
panellist
or
fieldworker
problems;
(iii)
reduced the
risk
of
'slippage'
in the com-
pletion
of the
diary by
the
panellists,
result-
ing
in undesirable
'completion
by
recall',
or
possibly
withdrawal
from
the
survey.
Careful
panel
recruitment
by
trained
and
experienced
fieldworkers
As noted
above,
the
recruitment
phase
is
arguably
the most arduous
phase
of
such
surveys.
It is
a
phase
that
should not
be
rushed
in
any way,
and
which
must
be
carefully
prepared
and
adequately
costed. Once
again
the
main
survey
benefited
considerably
from
the
experience
of the
pilot
survey.
Suitable
panel
remuneration
nd incentives
Previous
studies
have shown that
cash rewards
to
panel
70
600-
580-
E
560-
-6540-
ai
Z
520-
500-
480-
8/11/2019 622250
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Methodological
spects
f
theconduct
f
a
long-term
anel
urvey
members
undoubtedly
reduce
panel
attrition. In
the
Cardiff
survey
panellists
received
?4
at
the
end of each
four
week
period
for
which
diaries had
been
successfully
completed,
plus
a ?1 bonus for
remaining
on the
panel
for the
full 24
weeks.
Whilst
such limited financial ncentives did not retainpanel
members
who
had become
seriously
disaffected,
they certainly
influenced
marginal
cases
and,
perhaps
more
importantly,
gave
the
majority
of
panellists
the
sense
of
doing
a
job
which was
'valued'.
An additional incentive was
provided
in the form
of
a
series
of
letters
from Research
and
Marketing
Ltd
(see
Guy
et
al.,
1983).
These
explained
the
purpose
of the
study,
encouraged panellists
to
remain to
the end of the
monitoring
period
once
they
were
three-quarters
of the
way
through,
and,
in
general,
encouraged
them
to
take
an interest
in
participation.
Fieldworker
control In
long-term
panel
surveys
there
is
a
danger
that
fieldworkers
as
well
as
panel
members will
begin
to lose
interest,
and that
the
quality
of the
survey
will
begin
to decline. For this
reason,
it
is
essential
that
fieldworkers
are
closely
supervised
and
generally encouraged
throughout
the
survey
period.
In the Cardiff
survey
fieldworkers
were
supervised
by
Researchand
Marketing
Ltd and
were
in
regular
and
frequent
personal
contact with
the fieldwork supervisor and office staff. Completed
diaries were examined
by
the
office
staff,
and
each
fieldworker
was
given
lists of the
remaining
errors made
by
his/her
panellists.
In
this
way
data
quality
was
continuously
monitored and maintained
through
a
process
of
supervisor/fieldworker/
panellist
feedback.
The
services
of
a
professional
market
research
organization
Long-term
panel
surveys
demand
a
large
number
of
trained
and
experienced
fieldwor-
kers, supervisors,data coders, processing controllers
and
so
on.
The
Cardiff
survey
benefited
considerably
from the
services
of a
professional organization
which had the
necessary
expertise
and
experience
in
this
area,
and
which was
committed to
the
require-
ments of an
academic
project.
In
terms of cost-
effectiveness and data
quality
the location
of this
organization
within
the
study
area itself was also
extremely
important.
In the authors' view this use
of
a
professional organization
is essential to the
success
of a
long-term
panel
survey.
Although
it
may,
at
first,
appear
to
be
unnecessarily
expensive,
it will
generally
be uneconomic
and
inefficient to
attempt
to
take on such
a
task
'in-house' and
to
attempt
to
set
up
such
an
organization
for the
purposes
of a
single
academic
project.
Thesecondquestionnaire
During
the
middle weeks
of the
main
monitoring
period
those households who
were still members
of
the
panel
were
asked
to
complete
a
much
more
detailed
questionnaire
relating
to their
demographic
and
socio-economic characteristics
and
their
attitudes
to
shopping
(for
further details
see
Guy
et
al., 1983,
pp.
89-108).
Since certain
types
of
analysis
of the
panel
data
require
information derived
from
this
questionnaire
(for
example
the
relationship
between observed
shopping
habits and household
characteristics),
high
response
rate
was
essential.
In
the
event,
a
response
rate of 98
per
cent was
achieved,
which was
largely
due to the
timing
of
the
questionnaire.
By
the middle weeks of the
main
monitoring
period
most
panellists
had
developed
a
personal
commitment to their
fieldworker,
were
taking
an active interest
in
completing
their
diaries,
and were thus
willing
to
fill in an additional
questionnaire.
In
addition,
a
further
small cash incen-
tive was
offered to
panellists
for
their
participation
in
the second
questionnaire.
Supplementarynformation
Given
the
large
costs
and
long
start-up
times
involved
in
mounting
a
long-term
consumer
panel
survey
it
is
important
that smaller
lower-cost
proj-
ects be co-ordinated with
the main
monitoring
period.
In
the Cardiff
survey,
the two
most
import-
ant of these
were
a
survey
of
grocery
prices
in
stores
frequented
by
the
panellists
(Guy
and
O'Brien,
1983),
and the collection of information on stores
visited
by
the
panellists,
including
details
of
owner-
ship,
store
type,
exact
location,
goods
sold,
and
floorspace
(see
Guy
et
al.,
1983,
pp.
126-33,
155-57).
In
addition,
a
careful
scrutiny
of the
local
press
was maintained for
any
events
likely
to influence
shopping
behaviour,
such as
major
promotions
involving
stores
in
Cardiff,
incidents
affecting
accessibility
to
shopping
centres,
and the
opening
or
ownership
changes
of stores.
In
fact,
such events did
take
place
during
the main
monitoring
period
of the
survey
and this
type
of
supplementary
information
may
be
important
in
suggesting
research
topics
and/or
in the
interpretation
of
certain
aspects
of
recorded behaviour.
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NEILWRIGLEYETAL.
REMOVAL
OF
NON-CONTINUOUS
REPORTERS
The
standard
commercial
practice
is to
remove
for
analysis
purposes
those
panellists
who
have
'unacceptable'gaps
in
the
continuity
of
their
pur-
chasing
records.
However,
there
is little concensus
on the
definition of
'unacceptable',
except
that
absences of
occasional
days,
weekends
or
periods
of
less
than
a week are
acceptable.
In
these
situations,
the
panellists
are
likely
to
adjust
their
weekly
pattern
of
purchasing
to
compensate
and can be
regarded
as
just
'not
buying anything'
on
the
days
of
absence.
In the
Cardiff
survey,
detailed records
were
kept
for
each
panel
member of
diaries
satisfactorily
completed,
days
of
holiday
taken,
missing
diaries,
and
so on. At the end of
the
monitoring
period
the information was summarizedin the form of a
panellists-by-week
matrix,
and
'continuous' and
'non-continuous'
reporters
were identified
using
the
most
rigorous
approach
in
current commercial
prac-
tice
(plus
the
addition of certain extra more
stringent
criteria-see
Guy
et
al.,
1983,
pp.
134-38 for
details).
On
this
basis,
27
panellists
were defined as
'non-continuous'
reporters
(in
most
cases because
they
took
an annual
holiday
of more than 15
days
during
the
monitoring
period).
This left
a
panel
of
454 'continuous'
reporters,
82
per
cent
(371)
of
which
had no absences of
more
than
seven
days
and
41 per cent (185) of which had not even a single day
away
from home
during
the
monitoring
period.
One of the
major
factors
influencing
the number
of non-continuous
reporters
is
clearly
the
timing
of
the
survey
in
relation to
major
holiday
periods.
In
the
UK,
the
optimum
timing
for
a six-month
panel
survey
is thus from
January
to
early July
since this
avoids the
major
holiday
periods
of
Christmas
and
late-July/August.
Shorter
term
panels
will also
benefit from
avoiding
these
periods
and other less
important
ones such as Easter.
DATA
QUALITY
Human
geographers
familiar
with the
response
and
non-response
error
problems
of
cross-sectional
or
short-term
panel
surveys may, initially,
find it rather
difficult to
accept
that the
quality
of data
supplied
in
long-term
panel
surveys
can be
maintained
over
lengthy monitoring
periods.
They
may
believe
that
panellists
will
rapidly
become
bored
by
the task
and
will thus
supply poor
quality
or even fabricated
data,
that fieldworker
motivation/performance
may
decline,
and that
the sheer size of the task will
inevitably
result in
larger
error
problems
than nor-
mal
at the data
editing/coding,
file creation
stage.
Essentially,
there are two
types
of
response
to such
beliefs.
First,
the
procedures
adopted
to maintain
data
quality
can
be
exposed
to critical
appraisal.
Second, summary measures of the information
obtained from
the
panel
can
be
compared,
for con-
sistency,
to the
results of other
surveys
and
analyses.
Techniques
f
quality
control
The
procedures
necessary
to maintain
the
quality
of
data
supplied
by
the
panellists
over
a
long
monitor-
ing
period,
and to maintain fieldworker motivation/
performance,
are
essentially
those
required
o reduce
panel
attrition
(discussed above)
and
they
need
not
be
repeated
here.
They
are
matters
which
must be
reviewed
in
detail,
and
on
which decisions must be
taken,
at the
design
stage. During
the course of the
survey,
data
quality
is
maintained
by
implementing
these
procedures
as
rigorously
as
possible,
but
with
sensitivity
at all times to the
crucial issues
of
fieldworker-panellist
contact
and fieldworker-
supervisor
control.
Overall,
there is
simply
no
sub-
stitute for a team of
experienced,
well-briefed and
highly
motivated
fieldworkers who
visit
panellists
and check their
diaries
at
least
every
fortnight,
and
who are backed
up
by
a
supervisory
system
which
monitors their
performance,
provides
the
necessary
advice
and
encouragement, and maintains con-
tinuous feedback from office
to
fieldworkers to
panellists
and vice versa.
Whatever
the
procedures adopted,
however,
and
despite
all the
efforts
of
the
fieldworkers,
t is inevit-
able that
occasional
response
errors
(incorrect
recording,
omission of
information,
over-reporting
and
so
on-see
Sudman,
1964)
will occur.
Neverthe-
less,
there is no evidence that
the
magnitude
of these
errors
is
any
greater
in
well-conducted
long-term
panel
surveys
than in cross-sectional or short-term
panel
surveys.
As
Ehrenberg
1972,
p.
8)
has noted:
Panel membersbecome
experienced
n
keeping
their
records
f
they
continue o
co-operate,
nd t
seems
that
the efficientand
satisfying
way
of
filling
out
a
diary
eachweek s to
try
anddo so more
or less
correctly.
Of
course,
there
will
always
be
a
small
number
of
panellists
who
persistently
provide
what
are
obviously
inadequate
records
of their
shopping
behaviour.
However,
such
panellists
are
readily
iden-
tified and can be
removed from the
panel
by
the
supervisory
staff.
In
the
Cardiff
survey, only
seven
72
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Methodological
spects
f
theconduct
f
a
long-term
anel
urvey
panellists
were
dropped
from the
panel
during
the
main
monitoring period
for this reason.
A
further
eature of the
quality
control
procedures
adopted
in
the Cardiff
survey
which
is
particularly
worthy
of
note,
was
the decision to sub-contract
the
transfer of edited and coded diaries to computer
tapes
to a
separate
and
specialized computing
firm
(DCMS
Ltd)
with
greater expertise
in the
design
and
implementation
of
large
error
checking
routines.
This decision enabled more than 30
consistency,
range
and
logic
checks to be
specially
designed
and
to be
performed
at the
point
of transferof the edited
and coded diaries to
computer tapes.
As
such,
it
provided
a
complementary
and
independent
level
of error
detection
to that
performed
in-house
by
Research
and
Marketing
Ltd
during
the
diary
editing
and
coding stages.
Errors
identified
by
DCMS
Ltd
were
reported
back to the staff of Research and
Marketing,
who
then
returned
to
the
original
diary
to check matters
of detail.
Any
amendments
which
were
then found
to be
necessary
were made to
both
the
computer tapes
and the
original
diaries.
Overall,
a
relatively
high
proportion
of the
budget
of
the
Cardiff
survey
(when
compared
to
previous panel
surveys)
was
allocated to
the error
checking process.
However,
it is
the
authors' view
that extensive and
specialized
error detection
systems
of this
type,
although
expensive
to
design
and
operate,
are
vital
to
the success of
complex surveys
which
produce
very
large
amounts
of
data.
Consistency
hecks
In commercial market research
there is
a
long
tra-
dition of
checking long-term
consumer
panel
data
for
consistency
against
other
sources,
such as retail
audit
and
factory
shipment
figures
and
against
data
from ad
hoc cross-sectional
surveys.
Indeed,
Ehrenberg
(1972,
p.
9)
has
argued
that
consumer
panel
data
are often
'amongst
the most
fully
checked
and
reproducible
that
are
available
in
the social
sciences'.
In
the Cardiff
survey,
two
types
of
consistency
checks have
been
performed.
The first
type
has
involved the
comparison
of
descriptive
statistics
obtained from the
Cardiff
survey
against
similar
measures obtained from other
contemporary
sources. For
example,
the
relationship
between
household income and food and
grocery expendi-
ture exhibited
by
the
Cardiff
panel
has
been
shown
to be
very
similar to that revealed in the
Family
Expenditure
Survey
of
1981
(Guy,
1983).
The second
type
of
consistency
check has con-
cerned the
predictability
of
a
number of
important
indices of consumer
purchasing
behaviour.
In
this
context,
it
has been shown that a
family
of models
widely
used in the statistics and
marketing
literature
to
study
brand
purchasing
behaviour
can
success-
fully predict,not only importantaspects of the brand
purchasing
behaviour
of
the
Cardiff households
(Wrigley
and
Dunn,
1983),
but also similar ndices of
purchasing
patterns
at individual stores
(Dunn
et
al.,
1983;
Wrigley
and
Dunn, 1984a,
b).
The
excellent
fit of
these models indicates that the Cardiff data
reveal the same
type
of
purchasing
regularities
as
previously
found
in a
wide
range
of
studies
in a
number of countries. As
such,
these
results
provide
considerable
support
for the
validity
of the Cardiff
data. The alternative
would
be
to believe that
panell-
ists within
a
wide
range
of
independently
con-
ducted
surveys
with different
designs
and different
operating procedures
could
somehow
produce
low
quality
(or
even fabricated
data)
in such a
way
as
to
consistently
produce
the
same
predictable
regularities
n
the internal
relationships
of
brand
and
store
purchasing
patterns-surely
a
very
difficult
belief to
support.
REPRESENTATIVE
NATURE OF
THE PANEL
Human
geographers sceptical
of
the
value of
con-
sumer
panel
data
often
question
whether
individuals
who are
prepared
to
take
part
in such
surveys
are in
some
way
different from
non-participants.
A
feature
of the Cardiff
survey
was that
its
design
allowed
some answers to
this
question
to
be obtained.
As
Fig
I
shows,
of the
initial 2012
households
sampled
in the
Cardiff
survey,
775 were not
contac-
ted or
refused to
answer the 'initial'
questionnaire,
and there
is
no
information
on
this
group
(other
than
knowledge
of sub-area in
which
each
non-contact/
non-respondent
is
located,
and the
approximate
numberof adults in each household).2 At this stage,
representativeness
of the
sample
must
rely
upon
the
fact that a
stratified
random
sample
design
was
used,
that three
attempts,
at
different
times of
day,
were made to contact
each
household,
and
that well-
trained and
experienced
fieldworkers
were used.
Certainly,
any
bias in the
representative
nature of
the
panel
which
may
have
arisen at this
stage
is not a
feature of
panel
survey
methodology per
se
but is
a
common
problem
of
all
social
surveys,
both
cross-sectional and
longitudinal.
Once initial
contact with
the
princi-al
food
73
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NEILWRIGLEY
TAL.
and
grocery shopper
of a household had been
established, however,
that contact had to
be
con-
verted,
if
possible,
into successful recruitment to
panel membership.
At
this
stage
the first
potential
bias
in the
representative
nature of the
sample
which
is directly attributable to the panel survey
methodology
occurs. At
this
stage,
632 contacts
refused
to
join
the
panel.
A
comparison
of
the
characteristics
of these
'non-panellists'
with
the
605
panellists
successfully
recruited,
and
using
data from
the
'initial'
questionnaire
completed
by
both
groups,
revealed
that
non-panellists
were
slightly
more
likely
to be
in the
age
category
55
plus,
from small
households,
and
to be male
(though
it
should be
noted that
overall
only
12
per
cent of
principal
ood
and
grocery
shoppers
were
male).
In
addition,
car
ownership
was lower
amongst
non-panellists.
Of
course,
the
initially
recruited
panel
is not the
final
panel,
and
it
may
be the case that those
panel-
lists who
'stay
the course' are different from those
who
drop
out
during
the
monitoring
period.
This
may
reinforce
or,
alternatively, may
counteract the
potential
bias to the
representative
nature of
the
panel
introduced
at the
previous
stage.
Using
infor-
mation from
the 'initial'
questionnaire
a
comparison
of
the 124
panellists
who
dropped
out of the
panel
during
the
monitoring
period
with
the 481
panellists
(the
'stayers')
who
remained,
was conducted.
This
revealed that
stayers
were
much more
likely
to
be
aged
25-44 and also members of
car-owning
households.
Approximately
twice
as
many
'stayers'
(32
per
cent)
as
'drop-outs'
(17
per
cent)
fell
into
this
category.
In
contrast,
'drop-outs'
were
dis-
proportionally
from
non-car-owning
households
and
aged
16-24 or 45
plus.
A further
breakdown
of the characteristics
of the
drop-outs
can
be obtained
by
dividing
them into
two
groups:
'immediate
drop-outs'
who left
the
panel
during
the
'running-in'
period,
and 'later
drop-outs'
who left
the
panel
during
the
main
monitoring period. A comparison of these two
groups
revealed that
'immediate
drop-outs'
were
much more
likely
to be older
(79
per
cent were
aged
45
or
over)
and
to be members
of
non-car-owning
households than was
the case for either
'stayers'
or
'later
drop-outs'.
In
contrast,
'later
drop-outs'
were
very
similar
to
'stayers'
in
most
respects,
with
the
one
minor
exception
that
'later
drop-outs'
were
more
likely
to
be
in
the
youngest age group,
16-24,
than
was the case for either
'stayers'
or
'immediate
drop-outs'.
On the basis of these
comparisons
it would seem
that
the Cardiff
panel
(and
we
suspect
long-term
panel
data in
general)
is
to
a
limited extent biased
towards
family
units in
which
the
panellist
is
aged
25-44.
Moreover,
these families tend to be
car-owners
and
are, therefore,
more mobile and
possibly more affluent.In addition, it would appear
that 'immediate
drop-outs'
who leave the
panel
during
the
'running-in'
period
are in some
respects
an
exaggerated
version
of
non-panellists
whereas
'later
drop-outs'
are
very
similar
to
stayers.3
This
pattern
of
over- and
under-representation
of
sub-
groups
must be borne in mind when
using
the data
for
certain inferential
purposes
or
to
draw
policy/
urban-planning
conclusions,
and
appropriate
correc-
tions
can,
where
necessary,
be made.
However,
the
degree
of bias should not
be
over-exaggerated,
for
the results of the much more detailed 'second
questionnaire'
show that the final
panel
of con-
tinuous
reporters
used for
analysis
purposes
includes
substantial numbers
of
virtually
every
type
of
population
sub-group
used
in the
description
and
analysis
of urban
shopping
behaviour
(including
the
old,
the
immobile,
the
unemployed,
and so
on).
Also,
it
in no
way
precludes
extremely
valuable com-
parisons
of the Cardiffresults with
those of
previous
short-term or
long-term
panel
surveys
reported
in
the
literature
of
geography, planning,
marketing
and
statistics
(including
the
government-financed
National Travel
Surveys),
as
these
surveys
are
likely
to be
subject
to similar imited
patterns
of
sub-group
over-
and
under-representation.
As
such,
the
Cardiff
data
provides geographers
with
an
immensely
useful
resource
for
understanding
the nature and
scale of
the
significant changes
in
shopping
behaviour
in
the
United
Kingdom brought
about
by
the
factors
described
in the introduction
to
this
paper.
CONCLUSIONS
It is our
belief
that
well-designed
and
rigorously
conducted panel surveys can provide high-quality
data of unmatchable
detail.
Moreover,
because
of
the recent
rapid
methodological
advances
in
panel-data
analysis,
such
data can be used to
provide
answers
to
a
range
of
problems
which
remain
ntrac-
table in the
presence
of conventional cross-sectional
data. In this
paper
we
have shown how
it is
possible
to collect
high-quality,
locationally
detailed,
infor-
mation from
a
panel
survey,
even when
the monitor-
ing
period
of the
survey
extends
over
a much
longer
time
horizon
than
that
typical
of
previous
geographical/planning
panels.
74
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Methodological
spects
of
the conduct
f
a
long-term
anel
survey
The rich
geographical
data base
provided
by
the
Cardiff Consumer
Panel
provides
a
unique
and
valuable resource
for
understanding
the nature of
urban
shopping
behaviour
in Britain in the
1980s,
and
for
understanding
the scale
and nature
of the
changes in such behaviour which have accompanied
the
transformation
of
the
British
grocery retailing
industry.
The
large
volume of research referred to
above,
either
completed
or still
in
progress,
gives
some indication of the
possible
uses of the
Cardiff
data.
We
hope
that this
paper
may
encourage
other
interested researchers to
exploit
the data base via
the
ESRC
Data
Archive,
and
that
it
will
encourage
both the
application
of
panel
data
techniques
in
urban
geography/planning
and a wider debate on
appropriate
survey
methodology.
ACKNOWLEDGEMENT
The
Cardiff Consumer
Panel
was
funded
by
the
Economic
and Social Research Council
under
grant
D00230010.
NOTES
1.
Households
n
each sub-areawere selected
by
random
sampling
of the
1981-82
electoral olls.
To
give
each
household
n
a
sub-area n
equal
chanceof
being
selec-
ted,
a
procedure
known as
'firsting'
Hoinville
and
Jowell,1978)
was
adopted
o correct or the fact
hatan
electoral
oll is not a
roster
of
householdsbut
a
list of
electors
those
eligible
to
vote,
i.e.
those
18
years
old
or over
approximately)
ho come fromhouseholds
f
varying
ize.As a
result,
he number f adults
18
years
old
or
over)
in
each of the 775
non-contact/
non-response
ouseholds
s known.
2.
See
1
above.
3. This
provides
an
additional
ustification
or
having
a
'running-in'
eriod,
and it should
be
noted
that the
similarity
between the
'later
drop-outs'
and
'stayers'
can be
exploited
by
those researchers
ho,
for some
analytical
urposes,
may
wish to
supplement
he size of
the final
panelby drawing
n the
incomplete
ecords
f
the 'later
drop-outs'.
REFERENCES
BROOM,
D. and
GUY,
C. M.
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