The effect of a direct payment or a lottery on questionnaire response rates: a randomised controlled trial: Table 1

Postal questionnaires are frequently used in research.2][3][4] An alternative, or complementary, approach to using lotteries is to make direct payments to survey responders.Few trials have evaluated direct payment compared with lotteries. 3 MethodsQuestionnaires about menopause services in the North West of England were sent to a random sample of 1000 women aged 40 to 65 during September to November 1997.The questionnaires included questions about use of hormone replacement therapy (HRT) and women's demographic characteristics.The sample of women were randomised in a 2 × 2 factorial trial to estimate the effectiveness of the two forms of incentive and their potential interaction within a single study.Unequal randomisation of 3 to 1 favouring no direct payment was used to minimise research costs, which led to unequal numbers in each of the four arms of the study (lottery alone, n =375; direct payment alone, n = 125; lottery and direct payment, n = 125; no lottery and no direct payment, n = 375).The direct payment consisted of £5 for each respondent while the lottery was for a prize draw of £50.Payment and/or inclusion in the prize draw were made on receipt of a completed questionnaire unless declined by respondents.Non-responders were sent up to two further mailings approximately one month apart.Women returning a blank questionnaire were not sent further mailings.To comply with the Data Protection Act, a Health Authority custodian attended with names and addresses for the three mailings.The investigators therefore had no information about the characteristics of non-responders.Analysis was by means of logistic regression using the SPSS statistical package.