Representativeness of participants in a cross-sectional health survey by time of day and day of week of data collection.

BACKGROUND General population health examination surveys (HESs) provide a reliable source of information to monitor the health of populations. A number of countries across Europe are currently planning their first HES, or the first after a significant gap, and some of these intend offering appointments only during office hours and/or weekdays, raising concerns about representativeness of survey participants. It is important to ascertain whether personal characteristics of participants vary by time of day and day of week of data collection, in order to determine the association between time and day of interview and physical examination on the results of data collected in HES. METHODS Multivariable regression models were applied to national HES in England to examine socio-demographic and health variations in three combined day-time periods of interview and physical examination: weekday daytime; weekday evening; and weekend. RESULTS The characteristics of participants interviewed or visited by a nurse varied by both time of day and day of the week for age, ethnicity, marital status, income, socio-economic group, economic activity and deprivation. People seen during weekday working hours had higher rates of poor self-reported health, limiting longstanding illness and obesity, and higher alcohol consumption, BMI and systolic blood pressure; adjustment for socio-demographic characteristics eliminated or substantially reduced these differences. CONCLUSION People responsible for planning surveys should be aware of participant preference for the timing of data collection and ensure flexibility and choice in times and days offered to optimise participation rates and representativeness.