statsby and alpha help

[Bryan Shelly]

I am trying to write the results of alpha to a file using statsby, a command with which I had not previously worked, for the source data at the bottom of this message. The command without statsby

alpha v*, item

works great and returns all the relevant results for alpha for each item. However, the basic statsby code

statsby, by(v*): alpha v*, item

does not return the relevant results for each item. Instead, it returns 19 observations that are a series of 0s and 1s that, frankly, might as well be random for all I know

* Example generated by -dataex-. To install: ssc install dataex
clear
input byte(v12570069 v12570679 v12571087 v12791904 v12803332 v12855959 v12855960 v12855962)
0 0 0 0 1 1 1 1
0 0 0 1 0 0 0 1
0 1 1 1 0 1 0 1
0 1 1 1 1 0 1 1
0 1 1 1 1 0 1 1
0 1 1 1 1 1 0 0
1 0 0 1 1 0 0 1
1 0 0 1 1 0 1 0
1 0 0 1 1 0 1 1
1 0 0 1 1 0 1 1
1 0 0 1 1 0 1 1
1 0 1 1 1 0 1 0
1 0 1 1 1 1 1 1
1 1 0 1 1 0 0 0
1 1 0 1 1 0 1 0
1 1 0 1 1 0 1 1
1 1 0 1 1 1 1 1
1 1 0 1 1 1 1 1
1 1 1 1 1 1 1 0
. . . . . . . .
end

I have played around with changing the term in the by parantheses. Leaving a blank

by()

gets me an output with the test level Cronbach's alpha, but not all the statistics for each item that I need. If I specify each variable individually, I can get their individual alpha coefficient to show up. So

statsby, by(v12570069): alpha v*, item

yields

* Example generated by -dataex-. To install: ssc install dataex
clear
input byte v12570069 float(alpha k cov)
0 .8634465 109  .01164183
1 .6299615 110 .002703245
end

The correct Cronbach alpha for v12570069 is displayed in the zero line, but it's missing the item-test etc stats I also need, and obviously I don't want a separate command and file for each individual item.

I have spent hours with both the help files on statsby and the one post on this board that referenced alpha and statsby together and am still hitting a brick wall.

Thanks in advance,

Bryan


SOURCE DATA BELOW

* Example generated by -dataex-. To install: ssc install dataex
clear
input byte(v12570069 v12570679 v12571087 v12791904 v12803332 v12855959 v12855960 v12855962)
1 . . . 1 0 0 1
1 . . . 1 1 0 0
1 . . . 1 1 1 1
1 . . . 1 1 0 1
1 . . . 1 1 1 1
0 . . . 0 0 1 1
1 . . . 1 1 1 1
1 . . . 1 0 1 1
1 . . . 0 1 1 1
0 . . . 1 1 0 1
1 . . . 1 1 1 1
1 . . . 1 1 1 0
0 . . . . 0 0 1
. . . . 1 . . .
1 . . . 1 1 1 1
1 . . . 1 0 1 1
1 . . . 1 1 1 1
1 . . . 1 1 1 1
1 . . . 1 1 1 1
1 . . . 1 1 1 1
1 . . . 1 1 1 0
1 . . . 1 1 1 1
0 . . . 1 0 1 1
0 . . . 1 0 1 1
1 . . . 0 0 0 1
1 . . . 1 0 0 0
1 . . . 1 0 1 1
1 . . . 1 0 1 1
1 . . . . 1 0 1
0 . . . 0 0 0 1
0 . . . 1 0 1 0
1 . . . 1 0 1 0
0 . . . 1 0 0 0
1 . . . 1 0 1 0
1 . . . 1 0 1 0
1 . . . 1 0 1 1
1 . . . 1 0 1 0
1 . . . 1 0 1 1
1 . . . 0 0 0 0
1 . . . 1 0 1 0
1 . . . 0 0 1 1
0 . . . 1 0 1 0
1 . . . 1 1 1 1
0 . . . 1 0 0 0
1 . . . 1 1 1 0
1 . . . . 0 1 1
1 . . . 1 1 1 0
0 . . . 1 1 1 1
1 . . . 1 0 1 1
0 . . . 1 0 0 0
0 . . . 1 0 1 1
1 . . . 1 0 0 0
1 . . . 1 1 1 0
1 . . . 1 0 1 1
1 . . . 1 1 1 1
1 . . . 0 0 1 1
0 . . . 0 0 0 0
1 . . . 1 0 1 1
0 . . . 0 0 0 1
1 . . . 0 0 0 1
0 . . . . 0 0 1
1 . . . 1 1 1 1
0 . . . 1 1 0 1
. . . . 0 . . .
1 . . . 1 0 0 1
1 . . . 1 1 0 1
1 . . . 1 0 1 0
1 . . . 1 1 0 1
1 . . . 0 0 1 0
1 . . . 1 0 1 1
1 . . . 1 1 1 1
1 . . . 1 0 1 1
1 . . . 1 0 1 1
1 . . . 1 1 1 1
1 . . . 1 1 1 1
1 . . . 1 0 1 1
0 . . . 0 0 1 1
1 . . . 1 0 1 0
0 . . . 1 0 1 1
0 . . . 1 0 0 0
1 . . . 1 1 1 1
1 . . . 1 1 0 0
1 . . . . 1 1 0
1 . . . 1 0 0 0
0 . . . 0 1 1 0
0 . . . 1 1 1 0
1 . . . 1 0 0 1
1 . . . 1 0 1 1
0 . . . 1 1 1 1
1 . . . 1 0 1 1
1 . . . 1 1 1 1
1 . . . 1 0 1 0
1 . . . 1 1 1 1
0 . . . 1 0 1 0
0 . . . 0 0 0 0
1 . . . . 0 1 1
1 . . . 1 0 1 1
1 . . . 1 1 1 1
0 . . . 0 0 0 0
0 . . . 0 1 0 0
end

[Oded Mcdossi]

The post you are referring to is irrelevant to your case. You don't have by variable as your data is not cross-sectional or panel for example. I think what you just need is a method to export your result to external file. If that is all what you need, then:

clear*
input byte(v12570069 v12570679 v12571087 v12791904 v12803332 v12855959 v12855960 v12855962)
0 0 0 0 1 1 1 1
0 0 0 1 0 0 0 1
0 1 1 1 0 1 0 1
0 1 1 1 1 0 1 1
0 1 1 1 1 0 1 1
0 1 1 1 1 1 0 0
1 0 0 1 1 0 0 1
1 0 0 1 1 0 1 0
1 0 0 1 1 0 1 1
1 0 0 1 1 0 1 1
1 0 0 1 1 0 1 1
1 0 1 1 1 0 1 0
1 0 1 1 1 1 1 1
1 1 0 1 1 0 0 0
1 1 0 1 1 0 1 0
1 1 0 1 1 0 1 1
1 1 0 1 1 1 1 1
1 1 0 1 1 1 1 1
1 1 1 1 1 1 1 0
end

alpha v*, item
mat alpha=r(Alpha)'
mat total=J(1,1,r(alpha))
mat rown total= Test_scale
mat alpha_total=alpha\total
mat li alpha_total

putexcel set alpha_results, sheet("alpha results") modify
putexcel A1="Cronbach's alpha statistics" 
putexcel B2="Item"
putexcel C2="alpha"
putexcel B3=matrix(alpha_total), rownames

[Bryan Shelly]

Oded,

Thanks so much. Your method got Cronbach alphas for each variable exported to xls, which is great progress. However, I also need the other statistics associated with the alpha command (specifically item-test correlation and item-rest correlation) for each variable as part of that export. Thoughts?

Thanks again,

Bryan

[Oded Mcdossi]

You can find all the return results from the alpha command by typing return list.

alpha v*, item
return list
mat alpha=r(Alpha)',r(ItemTestCorr)',r(ItemRestCorr)'
mat total=J(1,3,r(alpha))
mat rown total= Test_scale
mat alpha_total=alpha\total
mat alpha_total[`=r(k)+1',2]=.
mat alpha_total[`=r(k)+1',3]=.
mat li alpha_total

putexcel set alpha_results, sheet("alpha results") modify
putexcel A1="Cronbach's alpha statistics" 
putexcel B2="Item"
putexcel C2="alpha"
putexcel C3="Item Test Corr"
putexcel C4="Item Rest Corr"
putexcel B3=matrix(alpha_total), rownames

[Bryan Shelly]

Ahhh ok, return list is what I forgot. It's obviously been a while since I've had to use it. Thanks again Oded!