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RESEARCH STUDIES


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RESERCH STUDIES

THE EPIDEMILOGICAL STUDIES CLASSIFICATION

DESCRIPTIVE STUDIES: - Individual Case report

Case series

- Population Correlation

Transverse


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RESERCH STUDIES

THE EPIDEMILOGICAL STUDIES CLASSIFICATION

ANALITIC STUDIES:

- Observational Case control

Cohort study

- Experimental Randomized clinical studies

Clinical trials

Therapy equivalence studies


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RESERCH STUDIES

COHORT STUDY


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COHORT STUDY

Longitudinal studies of incidence

Offers the best information regarding the causality

Compares two similar groups (exposed unexposed) from the samepopulation (cohort)

Direct appreciation of the risk

Types of cohort studies: - prospective

- retrospective

- bidirectional


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COHORT STUDY

THE DESIGN OF COHORT STUDY

Objective: demonstrates the importance of a factor in a diseaseetiology.

The study begins from a population (cohort) without a disease,

which is stratified in two similar subgroups (lots): the groupexposed and unexposed to the risk factor


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COHORT STUDY

COHORT STUDY DIAGRAM

populationpersonswithoutdisease

exposed

unexposed

with disease

without disease

with disease

without disease

study direction

futurepresent


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COHORT STUDY

For the group exposed to the risk factor we have to specify:

The assumed risk factors and the ways of their measurement

Subjects eligible criteria ( age, sex)

Tracking period

The measurement that needs to be taken in order to prevent asubjects loss from the study

The defining of the used diagnosis procedures


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COHORT STUDY

The dates are placed in a contingency table 2x2

With

disease

Without

disease

TOTAL

Exposed to the

risk factor a b a+b

Unexposed to

the risk factor c d c+d

TOTAL

a+c b+d a+b+c+d


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COHORT STUDY

DATA ANALYSIS

Incidence =

Incidence comparison can be done :

- as proportion (relative risk)

- as difference (attributable risk)

No. of cases with disease in a period of time p

total number of population


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COHORT STUDY

RELATIVE RISK = the ratio between the disease incidence from the personsexposed and unexposed to the risk factor.

R1 = disease risk in exposed groupR0 = disease risk in unexposed group

Relative risk shows how many times the disease risk is greater in exposedgroups than the disease risk in unexposed group.

RR

0

1

dc

cba

a

RR


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COHORT STUDY

ATTRIBUTABLE RISK = the difference between the disease risk inexposed and unexposed group.

RA = R1R0

Attributable risk shows with how much is greater the risk in theexposed group than in the unexposed group.


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COHORT STUDY

INTERPRETATION:

RR RA

>1 >0 association risk factor disease

=1 =0 indifferent factor


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COHORT STUDY

STATISTICAL ANALYSIS OF THE COHORT STUDY

The adequate statistic test is Chi test.

If the result of the statistical analysis is a p value smaller than0,05 then we get a statistically significant result.

IC = confidence interval = 95%


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COHORT STUDY

ADVANTAGES: Good validity

Offers the best information regarding the causality and the naturalhistory of the disease

The most efficient measurement of the risk (RR)

They are efficient in diseases with higher incidence

Can observe the mechanism of action of the risk factor

Can observe the late effects of the disease


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COHORT STUDY

DISAVANTAGES:

Expensive

Cant be repeated

Requires a long time to finish and a large number of subjects

Long-term observation is difficult when the disease has a long

latency period

Produce errors, especially selection and confusion errors


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COHORT STUDY

Testing the following hipothesys was wanted: oral breathing during thechild's growing period favors the appearance of the maxillary compressionsyndrome. For testing the hipothesys, a study in Tirgu Mures was initiated,in which children from 5 kindergardens were included. The children of bothgroups were between 3 and 4 years old and had similar characteristics

regarding sex distribution, background, feeding habits, the presence ofdento-maxillary anomalies in parents or siblings, the harmoniousdevelopment of the cephalic end, dimentions , intermaxillary and occlusalrelations. 51 children were exposed to the risk factor studied. They wereoral breathing either due to upper airways' obstruction, septumdeviations/adenoids whose surgical treatment was refused by the parents

or treatment-refractory rhinitis. The group of children not exposed to therisk factor, didn't present oral breathing at rest, and their upper airways'permeability was normal. The maxillary growth of the children in bothgroups was kept under observation for 4 years, tracking the possiblestarting symptoms of the maxillary compression syndrome.