Background: Accuracy of incidence estimates may be affected by biases that depend on frequency of approach to reporters and reporting window length. A time-sampling strategy enables infrequent approaches with short windows but has never been evaluated.
Methods: A randomized crossover trial compared incidence estimates of work-related diseases using time-sampled versus continuous-time reporting. Physicians were randomly allocated either to report every month (12/12) in 2004 and for 1 randomly chosen month (1/12) in 2005, or to the reverse sequence. Numbers of new cases of work-related disease reported per reporter per month for 1/12 and 12/12 reporting periods were compared.
Results: Response rates were high (87%). Withdrawal from the study was higher under 12/12 reporting. The rate ratio for 1/12 versus 12/12 reporting was 1.26 (95% confidence interval = 1.11-1.42). Rates declined gradually in the 12/12 groups over the year, consistent with reporting fatigue.
Conclusions: Increased frequency of data collection may reduce incidence estimates.
From the aHealth Methodology Research Group, University of Manchester, Manchester, United Kingdom; bCancer Institute, New South Wales, Australia; and cOccupational and Environmental Health Research Group, University of Manchester, Manchester, United Kingdom.
Submitted 10 February 2009; accepted 22 September 2009; posted 9 March 2010.
Supported by the UK Health and Safety Executive contribution to the funding of OPRA. Grant No: 4307/R56.069 & 4496/R60.002.
Correspondence: Roseanne McNamee, Health Methodology Research Group, Jean McFarlane Building, University Place, University of Manchester, Oxford Rd, Manchester M13 9PT, England. E-mail: email@example.com.