I`m conducting the translation of a very short scale of 12 ítems to assess therapeutic alliance in children. I have 61 answers and I wonder if that number of subjects it`s acceptable to run Exploratory Factor Analysis. I know that there is a suggestion of 5 participants for item to do EFA and 10 participants for item to do CFA. However, the number of participants here seem to be very smal for these analysys. What it´s your opinion?
Hello Leandro,
The vague answer is, more cases is generally better than fewer cases. There are two reasons:
1. The factor model you seek must, ideally, be capable of providing good estimates for the (12*11/2 =) 66 unique observed relationships among your 12 variables (here, item scores). That's a lot to ask of 61 cases.
2. In general, the smaller the N of cases, the more volatile are the observed relationships among the variables from sample to sample. Hence, the less likely that your sample data will accurately represent the correlations that may exist in the population. As these correlations are what the EFA is intended to account for, if they are incorrect then you likely will identify a factor model that does not generalize well to the population. The literature is full of studies in which one set of authors using a small or modest sample claims their EFA shows "different" results than those from another set of authors, even if ostensibly drawing from the same population.
Can you still proceed? Yes, of course--the numbers won't leap up from your data file and protest! However, do be mindful that: (a) guidelines such as "at least 100 cases" and "10-20 cases per variable" for EFA abound; and (b) you likely would want to characterize your results as tentative or exploratory, rather than as a definitive solution to the question of the true factor structure.
Good luck with your work.
As David Morse said, "guidelines such as "at least 100 cases" and "10-20 cases per variable" for EFA abound" but if you look hard enough, you can find some sources that say 5 cases per variable is enough.
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