This question came up in a consulting context, and I was interested in your thoughts.
One strategy for dealing with occasional missing data when calculating scale means looks like this in the language of SPSS:
COMPUTE depmean = mean.4(dep1, dep2, dep3, dep4, dep5, dep6). EXECUTE.
I.e., calculate the mean of a psychological scale such as depression by taking the mean of six items. If a participant has four or more non-missing items, return the mean of the non-missing items. If the participant has three or fewer non-missing items, return missing.
Of course the number of items in the scale and the threshold number items for calculating the mean can vary.
- In general, under what conditions, would you see this method of dealing with missing data to be appropriate?
- If you perceive it to be inappropriate, what alternative procedure would you recommend?