Wilcoxon/ t-test, z-standardization

Posted by Tom on Aug 24, 2012; 12:24pm
URL: http://spssx-discussion.165.s1.nabble.com/Wilcoxon-t-test-z-standardization-tp5714842.html

Hello

 

I’m confused about the right proceeding: I got two variables, “time” measuring the amount of time for a task (5-point Likert-scale) , the other (“benefit”, 4-point Likert scale) is the estimated benefit of the used time. If the difference between “benefit” and “time” is positive, the time spent on the task is a somehow efficient investment, if the difference is negative, the time spent on the task doesn’t worth the investment.

So far my intention.

 

My first idea was to calculate a paired t-Test (N= 150), but I’v got a problem with the different scales.

My second idea was to do a z-transformation and then to do the t-test with the z-standardized variables.

My third idea was to run a nonparametric analysis, Wilcoxon (just in case, ).

My forth idea is to run a t-test on the new variable “difference” (“z-benefit” – “z-time”) to test, if “difference” differs significantly from zero (zero means, that the time spent is in accordance with the benefit).

 

Now my results:

-       Paired T-test with the z-standardized variables: no significance.

-       Wilcoxon with original variables: no significance.

-       Wilcoxon with the z-standardized variables: significance!

 

Which requirements I have to look at in order to decide for a certain test in this case? What about my considerations? I appreciate any help, thanks.

Tom