Applying T-test on fraction of respondents

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Bartyboy
Posts: 13
Joined: Mon Apr 07, 2014 10:59 am

Applying T-test on fraction of respondents

Postby Bartyboy » Mon Apr 07, 2014 3:53 pm

Hey there everyone.

I'm in the following situation:

100 respondents filled in my questionnaire:
--> The first 50 persons got Code 1 (They are assigned to Condition 1)
--> The last 50 persons got Code 2 (They are assigned to Condition 2)

I now want to execute an independent T-test within condition 1 ( 50 people) and within condition 2 ( also 50 people) SEPERATELY.
I have been searching for solutions but found nothing so far...

Could someone help me out ?
GerineL
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Joined: Tue Jun 10, 2008 4:50 pm

Re: Applying T-test on fraction of respondents

Postby GerineL » Tue Apr 08, 2014 8:51 am

use select cases.

You sure you want to do this though?
Bartyboy
Posts: 13
Joined: Mon Apr 07, 2014 10:59 am

Re: Applying T-test on fraction of respondents

Postby Bartyboy » Tue Apr 08, 2014 9:13 am

@ Gutnr

Hey,
I have to compare 2 means within each condition.

Within condition 1 ( first 50 people) there is a before(no manipulation of dependent variable) and after(manipulation of dependent variable) measurement which I have to compare for significant difference or not...

This also applies to condition 2. ( the other 50 people)

Is my reasoning correct in this case ?
GerineL
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Re: Applying T-test on fraction of respondents

Postby GerineL » Tue Apr 08, 2014 9:38 am

no, use repeated measures with pre/post as within subject and treatment condition as between subject factor.
Bartyboy
Posts: 13
Joined: Mon Apr 07, 2014 10:59 am

Re: Applying T-test on fraction of respondents

Postby Bartyboy » Tue Apr 08, 2014 1:38 pm

Hey,

I'm using some scales (General sens of power of Anderson & Galinsky ) that have been tested in literature before.
But... here's my confusion:

Altough the scale items have been tested before (by other authors) on internal consistency via cronbach's alfa,
My SPSS output tells me a few scale items should better be removed.

Should I remove those scale items ?

Greetz
GerineL
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Re: Applying T-test on fraction of respondents

Postby GerineL » Tue Apr 08, 2014 1:42 pm

that's not something you can answer easily, there is discussion about this.
Some people will indeed remove those items, others may just use the original scale.

just to be sure: did you recode the appropriate items?
and are you sure you should remove them (i.e., is it a strong effect?)
Bartyboy
Posts: 13
Joined: Mon Apr 07, 2014 10:59 am

Re: Applying T-test on fraction of respondents

Postby Bartyboy » Tue Apr 08, 2014 3:05 pm

I did recode the appropriate items

Effects are in the range of 0,7 . Some are even less
GerineL
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Re: Applying T-test on fraction of respondents

Postby GerineL » Wed Apr 09, 2014 7:48 am

did you look at scale if item deleted?
Bartyboy
Posts: 13
Joined: Mon Apr 07, 2014 10:59 am

Re: Applying T-test on fraction of respondents

Postby Bartyboy » Thu Apr 10, 2014 9:29 am

Yes I did.

Gutnr I applied a paired samples t-test...
with 4 pairs:
1) Initial powerfeeling downstairs - powerfeeling upstairs (Condition 1)
2) initial powerfeeling upstairs - powerfeeling downstairs ( Condition 2)
3) Need for power downstairs - need for power upstairs (Condition 1)
4) Need for power upstairs - need for power downstairs (Condition 2)

I tried repeated measures but find it rather complex to use...


Does this gives me the same results as an repeated measures ?

Greetz
GerineL
Moderator
Posts: 1477
Joined: Tue Jun 10, 2008 4:50 pm

Re: Applying T-test on fraction of respondents

Postby GerineL » Fri Apr 11, 2014 10:11 am

you don't take into account the interdependency between some variables like this.
try to look at some case studies for a 2x2 design

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