Slide 2 KNR 445 Statistics t-tests Slide 1 Standard Scores
Comparing scores across (normal) distributions z- scores 1 Slide 3
KNR 445 CT/Spread & Z-scores Slide 2 Assessing the relative
position of a single score Move from describing a distribution to
looking at how a single score fits into the group Raw Score: a
single individual value i.e. 36 in exam scores How do we interpret
this value how good is it? 1 Slide 4 KNR 445 CT/Spread &
Z-scores Slide 3 Describe the typical and the spread, and the
number of cases Minimal Statistics Mean SD N Z-SCORE: identifies a
score as above or below the mean AND expresses a score in units of
SD E.g. z-score = 1.00 (1 SD above mean) z-score = -2.00 (2 SD
below mean) 1 Slide 5 KNR 445 CT/Spread & Z-scores Slide 4
Z-score = 1.0: GRAPHICALLY Z = 1 84% of scores smaller than this 1
Slide 6 KNR 445 CT/Spread & Z-scores Slide 5 Calculating
z-scores Calculate Z for each of the following situations: 1 2 3 4
5 Slide 7 KNR 445 CT/Spread & Z-scores Slide 6 Other features
of z-scores Mean of distribution of z-scores = 0 (i.e. 0 = 0 SD) SD
of distribution of z-scores = 1 since SD is unit of measurement
z-score distribution is same shape as raw score distribution 1 2 3
Slide 8 KNR 445 CT/Spread & Z-scores Slide 7 Z-scores can
compare scores from different distributions Marys score SAT Exam
550 (mean 500 SD 100) Geralds score ACT Exam 24 (mean 18 SD 6) Who
scored higher? Mary: (550 500)/100 = ? Gerald: (24 18)/6 = ? 1 2 3
4 Slide 9 KNR 445 CT/Spread & Z-scores Slide 8 Z-scores &
the normal curve For any z-score, we can calculate the percentage
of scores between it and the mean; all scores below it & all
above it Applet demos:
http://psych.colorado.edu/~mcclella/java/normal/normz.html
http://psych.colorado.edu/~mcclella/java/normal/normz.html
http://psych.colorado.edu/~mcclella/java/normal/handleNormal.html
http://psych.colorado.edu/~mcclella/java/normal/handleNormal.html
http://psych.colorado.edu/~mcclella/java/normal/tableNormal.html
http://psych.colorado.edu/~mcclella/java/normal/tableNormal.html 1
2 3 4 5 Slide 10 KNR 445 CT/Spread & Z-scores Slide 9 Finding
z-scores in PASW Choose this option Slide 11 KNR 445 CT/Spread
& Z-scores Slide 10 Finding z-scores in PASW Slide the variable
over that you want converted to z- scores And choose this Slide 12
KNR 445 CT/Spread & Z-scores Slide 11 Finding z-scores in PASW
The z-scores pop up in the data window as a new variable 1 Slide 13
KNR 445 CT/Spread & Z-scores Slide 12 Finding z-scores in Excel
First compute the average for the variable 1 Slide 14 KNR 445
CT/Spread & Z-scores Slide 13 Finding z-scores in Excel Then
the SD 1 Slide 15 KNR 445 CT/Spread & Z-scores Slide 14 Finding
z-scores in Excel Then stick in the relevant formula in the first
cell (note use of $) 1 Slide 16 2 KNR 445 CT/Spread & Z-scores
Slide 15 Finding z-scores in Excel Then just copy down 1
