Comparison of early and delayed respondents to a postal health survey: a questionnaire study of personality traits and neuropsychological symptoms.

Delayed response to a mail survey is related to age, lifestyle and socioeconomic status, and may provoke bias in epidemiological study. We investigated whether delayed respondents were associated with their personality traits and neuropsychological symptoms. Two hundred and ninety-eight painters from a Scottish dockyard cohort and their 571 male controls (general subjects) randomly recruited from the local residents completed a questionnaire, which included 24 statements of the Eysenck personality scales and 22 questions of neuropsychological symptoms. There was a similar distribution of delayed response between general subjects and painters, with a total of 55.6% early (returning questionnaires within 4 weeks), 33.4% intermediate (within 8 weeks) and 11.0% late respondents (after 8 weeks). The delayed response was related to only a few individual statements or symptoms, which varied between general subjects and painters. There were no significant differences in scores in statements of personality traits and neuropsychological symptoms among the three respondent groups, except for the late respondents in painters having an increased score of total neuropsychological symptoms at borderline significance. After adjustment for confounding the case-control analysis showed no significant association of the high scores of social conformity, neuroticism and symptoms with a delayed response. This study suggests that response to a postal health survey may not be influenced or biased by personality traits and neuropsychological symptoms.