turn on suggestions

Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type.

Showing results for

Find a Community

- Home
- /
- SAS Programming
- /
- SAS Procedures
- /
- Nomiss Option in Proc CORR to Calculate Cronbach's...

Topic Options

- Subscribe to RSS Feed
- Mark Topic as New
- Mark Topic as Read
- Float this Topic for Current User
- Bookmark
- Subscribe
- Printer Friendly Page

- Mark as New
- Bookmark
- Subscribe
- Subscribe to RSS Feed
- Highlight
- Email to a Friend
- Report Inappropriate Content

10-23-2013 03:23 PM

Hi everyone,

I am looking help to solve the mystery in calculating cronbach's alpha WITHOUT "Nomiss" options in proc corr.

Here is my sample data:

and here is my code:

Proc Corr Data = test Alpha Out = temp1;

Run;

Then I got this result:

I have one missing value on X2.

I didn't use the "Nomiss" option and get a raw alpha of 0.61538.

However, if calculate the alpha manually based on the formula:

Alpha = K/(K - 1) * (1 - (Variance_X1 + Variance_X2) / Variance_(X1+X2)),

Since Variance_X1 = ((1-2)^2 + (2-2)^2 + (3-2)^2) / (3-1) = 1,

Variance_X2 = ((1-1.25)^2 + (1.5-1.25)^2) / (2-1) = 0.125,

Variance_(X1+X2) = ((2-2.83)^2 + (3.5-2.83)^2 + (3-2.83)^2) / (3-1) = 1.125,

and with K = 2,

I get alpha = (2/(2-1)) * (1 - (1+0.125)/1.125) = 0.

Does anyone know how SAS calculate the alpha in this example?

Thank you in advance!

- Mark as New
- Bookmark
- Subscribe
- Subscribe to RSS Feed
- Highlight
- Email to a Friend
- Report Inappropriate Content

Posted in reply to Siriustar

10-23-2013 03:32 PM

I think you're variance of (X1+X2) formula is incorrect, I get 0.875 but I suppose that depends on how you deal with the missing value, because you'd need that to calculate the Cov(XY).

Var[X + Y] = Var