Factor analysis of a sleep evaluation questionnaire

A self-completion sleep evaluation questionnaire (SEQ), consisting of 10 cm line analogue rating scale questions, was constructed to investigate subjects' responses to aspects of sleep and early morning behaviour. The questions were grouped into 4 chronological areas: the ease of getting to sleep (GTS), the perceived quality of sleep (QOS), the ease of awakening from sleep (AFS), and the integrity of early morning behaviour following wakefulness (BFW). Five hundred and one SEQs were completed during several investigations into the comparative effectiveness of hypnotic drugs. The classical factor analysis produced 4 factors which corresponded to the 4 aspects of sleep and early morning behaviour listed above. The GTS and QOS factors were positively correlated (+0.57), as were the AFS and BFW factors (+0.48). The 2 sleeping state factors (GTS and QOS) were orthogonal to the 2 waking state factors (AFS and BFW).