Can't run Independent-Samples T-test

#1
Hello, everyone,
I need a piece of your help on a popular question of Statistical Test Choosing :confused:

I have an Experimental Group and a Control Group
I have pre-test scores for both groups
the experimental group receives a treatment
then
I have Post-tests scores for both groups

my research question is whether the treatment has had any effect.

in my SPSS data I have separate variables for all the scores:
Control group Pre-test scores
Control group Post-test scores
Experimental group Pre-test scores
Experimental group Post-test scores

and the ID column. that's it,
so when i try to run the Independent-Samples T-test I have no Grouping variable... :(

Do I need to re-form my datasheet?
or
Do I need a different statistical test?

thanks in advance!
appreciate your help!!!
 

hlsmith

Less is more. Stay pure. Stay poor.
#2
You should subtract the post values by the pre values, then run your test on the differences between the two groups.
 

Karabiner

TS Contributor
#3
Do I need to re-form my datasheet?
Three columns, one for the group membership, one for
pretest and one for posttest scores. Possibly you can
then perform a repeated measures / mixed ANOVA with time
of measurement as within-subjects factor and group
membership as between-subject variable. The interaction
is what you are intersted in.

With kind regards

K.