factor analysis with missing values I have data on about 25 subjects and 30 variables with about 20 missing values. The data is missing at random. What will be the best approach to perform factor analysis. How is factor analysis versus principal component analysis in such cases where some data is missing? Thanks in advance. 
 A: In general, I agree with @ttnphns' comment in that you have to have a certain minimal number of cases per variable, with other metrics include loadings and number of variables per factor. This is addressed in the literature (i.e., MacCallum, Widaman, Zhang & Hong, 1999).
Having said that, this heuristic is not set in stone - people have different opinions on the topic and I ran across research that discusses conditions, when it is possible to obtain good results from factor analysis (FA) of small sample data sets ($N < 50$) and/or sample data sets with other questionable characteristics. In particular, aspects of applying FA to small sample data sets are discussed by Costello and Osborne (2005), de Winter, Dodou and Wieringa (2009) as well as Zhao (2009).
References
Costello, A. B., & Osborne, J. W. (2005). Best practices in exploratory factor analysis: Four recommendations for getting the most from your analysis. Practical Assessment, Research & Evaluation, 10(7). Retrieved from http://pareonline.net/pdf/v10n7.pdf
de Winter, J. C. F., Dodou, D., & Wieringa, P. A. (2009). Exploratory factor analysis with small sample sizes. Multivariate Behavioral Research, 44, 147–181. doi:10.1080/00273170902794206 Retrieved from http://www.3me.tudelft.nl/fileadmin/Faculteit/3mE/Over_de_faculteit/Afdelingen/BioMechanical_Engineering/Organisatie/Medewerkers/Winter/doc/exploratory_factor_analysis_with_small_sample_sizes.pdf
MacCallum, R. C., Widaman, K. F., Zhang, S., & Hong, S. (1999). Sample size in factor analysis. Psychological Methods, 4(1), 84-99. Retrieved from http://people.musc.edu/~elg26/teaching/psstats1.2006/maccallumetal.pdf
Zhao, N. (2009). The minimum sample size in factor analysis. [Website] Retrieved from https://www.encorewiki.org/display/~nzhao/The+Minimum+Sample+Size+in+Factor+Analysis
