Factor Analysis

[irinnew]

Hi experts!

I used the following statement to generate Factor Analysisfor 2 factors:
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proc factor DATA=OUT.Baseline priors=smc msa preplot plot ROTATE=varimax
SCREE;
Var Quest1-quest21;
Run;
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Below is my output:

FACTOR ANALYSIS FOR 21 QUESTIONS IN base
The FACTOR Procedure
Initial Factor Method: Principal Factors

Factor Pattern
Factor1 Factor2
Quest1 0.45597 -0.19266
Quest2 0.66878 -0.24750
Quest3 0.69659 -0.34760
Quest4 0.71305 -0.30869
Quest5 0.66067 -0.15974
Quest6 0.53918 -0.07605
Quest7 0.54150 0.16137
Quest8 0.44033 0.12523
Quest9 0.64622 -0.03362
Quest10 0.44721 0.02622
Quest11 0.39608 0.10904
Quest12 0.61444 -0.18887
Quest13 0.72177 -0.19362
Quest14 0.30203 -0.05209
Quest15 0.31181 0.07246
Quest16 0.35011 0.13703
Quest17 0.55858 0.35771
Quest18 0.63260 0.33366
Quest19 0.52697 0.35495
Quest20 0.46168 0.15807
Quest21 0.59462 0.36410

Variance Explained by Each Factor
Factor1 Factor2
6.4037578 1.0239459
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My question is:
How can I get Three factors? How should I change my statement above?

Thank you in advance

Irin

 

[dqrose]

Are there actually more than two variables (or two responses to each question) in your dataset? You'll only be able to generate at most as many factors as there are variables: doing more would be rather like trying to find a new set of axes for an X-Y graph in three dimensions. I suspect that for whatever reason you have data that's essentially two-dimensional, and that therefore you can't get more than two dimensions in the output.

 

[irinnew]

There are 21 responses to questions in my dataset.

Depending on which survey/dataset I use in my code ,the output contains 2, 3, or 4 Factors. However the screen plot's "elbove" is not always obvious. That is why I would like to FORCE program to generate 3 factors instead 2 as code did and see how the result look like.

I assume there should be an option in the above code to let me FOURCE /increase the number of factors in the output.

How can I do it?

Thanks,

Irin

 

[dqrose]

There is an option to specify the number of factors: it's "Nfactors=3" (4, 5 or whatever), so presumably 2 is the default. My apologies: I assumed you had already tried that, and still failed to get the required number.

The syntax of all the options can be found in SAS's online help under "Factor procedure". I hope this helps - I haven't actually tried it out before posting this, but I'd be surprised if it didn't work.