Factor analysis of analogue scales measuring subjective feelings before and after sleep.

A series of 18 visual analogue scales was used to report the subjective feelings of 38 healthy subjects on 732 occasions during experiments concerned with the quality of sleep. Factor analysis of scores from these scales, both for all subjects combined and within each of four subjects separately, yielded two factors consistently -- 'alertness' and 'tranquillity'. Scores derived from the first factor indicated that, in the laboratory setting levels of immediately after waking in the morning were reduced, in relation to those before falling asleep on the previous night.