First, if you are doing principal components analysis, they are
components, not factors. PCA and EFA are different things, with
different aims (and it's the cause of massive amounts of confusion
that they have the same name).
Second, if you extract a different number of factors, you'll get
different solutions. Factor 1 in a 4 factor solution and factor 1 in
a five factor solution won't be the same.
I'm not sure what you mean when you say you retained 4 factors from 10
factors. If you have 39 items, then you have (potentially) 39
components. So you've retained either 4 or 10 from 39.
You should first decide how many factors to extract. Then extract
them and interpret. If you don't like it (because, as in your case,
they are uninterpretable), extract fewer, and try again.
You also don't mention anything about rotation.
Jeremy
2009/9/30 Mina Vasalou <[log in to unmask]>:
> Dear all,
> I have conducted principle component analysis on 39 items. I retained 4 factors from a total
> of 10 factors (the six remaining factors are not easy to interpret as items load highly on
> multiple factors). Andy Field's book chapter on PCA mentions re-running the analysis a
> second time, this time constraining the number of factors - in my case this would be 4.
> When I set the number of factors to 4, factors 3 and 4 now both load on the third factor and
> a new fourth factor emerges. Can anyone point me towards more information on if and why
> this step is necessary?
>
> Many thanks
> Mina Vasalou
>
--
Jeremy Miles
Psychology Research Methods Wiki: www.researchmethodsinpsychology.com
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