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I’ve run a pilot study with only 50 participants and I was wondering what I could actually do with a small sample like that, how can I best use this data before collecting the final sample of 600 participants. I will be doing an exploratory analysis and a confirmatory analysis. The goal is to validate a novel construct that is supposed to include 4 different sub-factors.

I did the EFA with the pilot study and it seems that the 4 factors formed a unique factor.

Are these preliminary results reliable, considering the small sample size? What else I could do?

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    $\begingroup$ That looks very small to get reliable results from CFA. Not sure why you want to do EFA first if you have a theory but people often do. $\endgroup$
    – mdewey
    Feb 22, 2021 at 17:22
  • $\begingroup$ Sorry, I meant that I will do the CFA, and also the EFA, with the final sample (N=600). So I can consider the results from the EFA, of the pilot study (N= 50), reliable and so change my research design based on this results? $\endgroup$
    – Zuzanne
    Feb 22, 2021 at 21:32

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Unless you strike really lucky I think 50 is too small.

MacCallum, R. C., Widaman, K. F., Zhang, S. and Hong, S. in a paper entitled "Sample size in factor analysis" published in Psychological Methods, in 1999 volume 4, 84-99. doi:10.1037/1082-989X.4.1.84 discuss this in much detail as there is no simple answer.

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The problem is that EFA (and CFA, kind of) is based on correlations. Look at the confidence intervals that you get on a correlation with N = 50. Here's a calculator: https://www.statskingdom.com/correlation-confidence-interval-calculator.html

A correlation of 0.3, with N = 50 has CIs from 0.02 to 0.53 - that's such a huge range that your correlations (and hence your loadings) will be all over the place - the same underlying population data could give rise to all sorts of different solutions.

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