I find that there are specific claims in SEM research that float around, but where they come from is often forgotten. So, I've made a list of these claims with some quotes and explanations below. Of course, I have also included a citation if the claim can be substantiated. If you have heard of a claim and know its source, feel free to email me and I'll determine if it should be added here.
Four Indicators Per Factor
Have you heard the one about the "optimal number of indicators" per factor? I have heard it a few times, and I know I have read it in multiple places. I include one of those sources below.
- Hair, J. F., Jr., Black, W. C., Babin, B. J., & Anderson, R. E. (2010). Multivariate data analysis (7th ed.). Upper Saddle River, NJ: Prentice Hall.
On page 678:
"In summary, when specifying the number of indicators per construct, the following is recommended:
- Use four indicators whenever possible.
- Having three indicators per construct is acceptable, particularly when other constructs have more than three.
- Constructs with fewer than three indicators should be avoided."
Joe's logic is that a minimum of three indicators are needed for identification, but four is a safer and more reliable configuration. More than four may result in a failure of unidimensionality (i.e., there may be multiple dimensions being captured). He also suggests four is the optimal number of indicators because it balances parsimony (simplest solution) with requisite reliability (all-else-equal: reliability increases as number of indicators increases).