1. Statistics in SPSS Lecture 3
Petr Soukup, Charles University in Prague

2. Descriptive stat II 2

3. Real data for lectures
ISSP 1999
Short info about data 3

4. Descriptive stat / review
LECTURE 1
Central tendency: ?
Dispersion = variance
Skewness
Kurtosis
TODAY’S LECTURE 4

5. Dispersion/Variance
Measure the size of difference between individual values (card. variable)
The well-known measure = variance (formula and logic by picture)
For real data analysis better to use standard deviation (why?)
Also range can be used (=MAX-MIN) 5

6. Variance in SPSS
More procedures, use more groups for comparison (DATA-SPLIT FILE)
ANALYZE-DESCRIPTIVE STATISTICS-DESCRIPTIVES
ANALYZE-DESCRIPTIVE STATISTICS-FREQUENCIES
ANALYZE-DESCRIPTIVE STATISTICS-EXPLORE
NEW 6

7. Skewness
Measure the shape of the distribution (card. variable), ?symmetric or not?
Skewed to the left or right (pictures)
Values for skewness 7

8. Kurtosis
Measure the „peak“ of the distribution (card. variable), ?big or small?
Platykurtic – low kurtosis or flat
Leptokurtic – low kurtosis or big peak 8

9. Skewness and kurtosis in SPSS
ANALYZE-DESCRIPTIVE STATISTICS-EXPLORE
Comparison of two groups
Standardized normal distribution as a benchmark 9

10. Box plot as special tool
Show many descriptive statistics in one picture
Very easy to describe your data
Example in SPSS: ANALYZE-DESCRIPTIVE STATISTICS-EXPLORE-PLOTS
Possible to compare groups 10

11. Missing values 11

12. Missing values System missing values (NO INFO)
User missing value (USER DEFINES)
Examples in SPSS
Impact of definition on descriptive statistics (income variable)
Always remember: Check your data and define missings if necessary (otherwise GIGO) 12

13. Data transformation (Creation of a new variable)13

14. Data transformation Use current variable(s) for creation of new one(s)
Many procedures
Most common:
RECODE
COMPUTE
COUNT 14

15. RECODE Change coding scheme of the variable
Can be saved in current variable or into new one
Examples in SPSS (gender, educational level) 15

16. COMPUTE
Compute new variable by mathematical formula (use current variable(s))
Examples in SPSS (age) 16

17. COUNT Compute occurence of specific value(s) in the set of variables
Examples in SPSS 17

18. HW 18

19. HW3
Try to describe one cardinal variable / i.e. mean, median, standard deviation, skewness and kurtosis. Compute and compare results for male and female. 19

20. Thanks for your attention20