I have a quite simple data pattern but find it hard to test a specific contrast I expected. I have 2 within subjects factors, each with two levels. Let's call them reward (high vs. low) and task pressure (high vs. low), while the dependent variable is performance (see the example GLM below). I expect that only one cell will deviate from all the rest, which do not differ from each other. Specifically, I expect that performance will be great when people get a high reward and are under high task pressure, but performance will be poor in all other conditions. Thus, I would like to test the specific contrast (3 -1 -1 -1).

I know how to do a similar contrast analysis within the levels of one variable, but not two as in this case.

I also know how to test the simple effect of one factor (reward) within one level of the other (high pressure) (I usually do this using a MANOVA syntax). Two of these simple effects analyses would give me the same information, but with less power, so that's not quite what I want.

Can somebody help me with this very specific contrast? I'd appreciate it very much if somebody could give me a useful SPSS syntax for this problem! I have looked in my standard statistics books and on the internet but all I ever come across are simple effects or contrasts within one factor.

Thank you very much in advance!

Marie

GLM reward1relax reward1rockon reward2relax reward2rockon

/WSFACTOR= reward 2 Polynomial pressure 2 Polynomial

/METHOD=SSTYPE(3)

/PRINT = descriptives

/CRITERIA=ALPHA(.05)

/WSDESIGN= reward pressure reward*pressure .