A sleep history recorded snoring, noisy breathing, ‘stopping breathing’ (apnoea), restless sleep, ‘overactive or difficulty in concentrating’ (daytime hyperactivity), daytime sleepiness (including difficulty in morning waking), and difficult behavior (as perceived by the respondent) during the day. Answers were classified either ‘not at all’ or ‘not often’, or ‘on most nights’. Symptoms on most nights were coded positive.