The relationship between the final factors and the composition of the original variance in a factor analysis is discussed, It is argued that, where factors defining intra individual processes are required, it is inappropriate to include interindividual variability in the original variance. A case study is reported illustrating this point. Factors defining intraindividual mood dimensions were obtained to assess differences in the self-rated mood of telephone operators as a function of switchboard design. Scores on a “well-being” factor were found to be lower for operators on a modern cordless switchboard than on the older style cord switchboard. The analysis also revealed significant changes in well-being and a second factor, labeled “competence,” over the working day.