Comparing two trends in proportions using SPSS
One can quite easily check for differences in linear trend in SPSS using the polynomial subcommand in the logistic procedure for frequencies (TAB5) and reading off the Wald (provided there are no inf MLES which there aren't here!):
For example suppose I have three genotypes, hsert, increasing in the presence of a particular aspect and two severity levels relating to the presence of absence of childhood maltreatment with two other columns containing the frequencies and the binary response. The first two entries might be something like the below
Tab5 |
Sert |
Maltreatment(Yes/No) |
Depression(Yes/No) |
|||
3 |
ll |
Yes |
Yes |
|||
16 |
ll |
Yes |
No |
|||
WEIGHT BY TAB5 . LOGISTIC REGRESSION dep /METHOD = ENTER hsert mal hsert*mal /contrast(hsert)=polynomial /CRITERIA = PIN(.05) POUT(.10) ITERATE(20) CUT(.5) .
Reference
Agresti A. (2002) Categorical Data Analysis. Second Edition. Wiley: New York.