Cronbachs Alpha- Quick question, urgent help needed

AGK

New Member
#1
Hi guys, hope you are all doing fine.
I have an exam on monday and need to know how to calculate Cronbach's alpha.
I know that you have to use the spearman brown formula when you shorten your scale. I can't quite figure out what to do when the scale gets longer.
Here is the example question I struggle with:

Imagine Cronbach's alpha for research A was 0.7. Which value for Cronbach's alpha can we expect when we extend the scale with 10 parallel items (the final scale has 15 items).
The expected value will be:
a) 0.44
b) 0.82
c) 0.88
d) 0.97

Does anybody know the formula I have to use in this case and how to calculate this ?

Thanks for helping!!
 

spunky

Super Moderator
#2
Hi guys, hope you are all doing fine.
I have an exam on monday and need to know how to calculate Cronbach's alpha.
I know that you have to use the spearman brown formula when you shorten your scale. I can't quite figure out what to do when the scale gets longer.
Here is the example question I struggle with:

Imagine Cronbach's alpha for research A was 0.7. Which value for Cronbach's alpha can we expect when we extend the scale with 10 parallel items (the final scale has 15 items).
The expected value will be:
a) 0.44
b) 0.82
c) 0.88
d) 0.97

Does anybody know the formula I have to use in this case and how to calculate this ?

Thanks for helping!!
The Spearman-Brown fomula works whether you're looking to increase or decrease the length of a scale, so you can use it to answer your question. It just depends on which constant you use to denote by which factor your tests are increasing or decreasing.