# Exploratory factor analysis using pooled longitudinal data

I am working on an analysis using exploratory factor analysis (EFA) with the common factor model. This question concerns a methodological issue. Any insights from someone who knows about EFA would be appreciated.

We measured the wellbeing of people using a 15 question survey. The same questionnaire was given the same 100 subjects at 3 different times (there were large gaps in time between when the surveys were administered, therefore we are assuming there was no time dependence [such as carry-over effect]). The goal is to use factor analysis to determine a fixed set of common factors and then calculate the factor scores and to compare the scores of subjects between time points.

Below is my strategy for the analysis. Does this sound reasonable?

Analysis Strategy: Combine all the data as it if were from a single location. That is to say, create a data set with 100 observations from time 1 and append the 100 observations from time point 2. Then append the 100 observations from time point 3. This would give a combined data set with a total of 300 observations.

Using the above data, fit an EFA model using all 15 variables and 300 observations and obtain factors. After computing the factor scores, again treat the data as if it were from 3 different time points (i.e. 100 subjects measured at three time points). Analyze the factors scores with i.e. ANOVA to test if factor scores of a factor change between the time points.

• I edited the question a bit - please check now. Also, to short: 1) 30 respondents is too few for really good FA on 15 items. 2) Appending 30 -> 90 is not a good idea: you treat the same respondent 3 times as if independent, which isn't true, and due to this may fall prey to spurious, due to nonhomogeneity, correlations. – ttnphns Apr 16 '13 at 13:51
• @ttnphns: Your edits are fine and make the question more clear. Thank you for taking the time. (1) I agree completely, we actually have around 100 respondents, thus the appended data would be 300 subjects. I was trying to give a simpler hypothetical situation. (2) While the 3 times could be dependent, for the analysis we are assuming independence, since there were 6 month gaps in time between when the survey was given. You make a good point though. I will make sure I assess this assumption. – Wade Apr 16 '13 at 17:12