| Time Period | |||||
---|---|---|---|---|---|---|
 | Before invitation | At invitation | After receipt of negative result | |||
 | Number sent | Number returned (%) | Number sent | Number returned (%) | Number sent | Number returned (%) |
Questionnaire reply rates a | Â | Â | Â | Â | Â | Â |
Cohort | 687 | 297 (43%) | 680 | 177 (26%) | 172 | 126 (73%) |
Cross-sectional | 624 | 250 (40%) | 763 | 241 (32%) | 146 | 101 (69%) |
All | 1311 | 547 (42%) | 1443 | 418 (29%) | 318 | 227 (71%) |
Analysis response rates b | Â | Â | Â | Â | Â | Â |
Cohort | 186 | 113 (61%) | 186 | 168 (90%) | 172 | 126 (73%) |
Cross-sectional | 175 | 105 (60%) | 244 | 229 (94%) | 146 | 101 (69%) |
All | 361 | 218 (60%) | 430 | 397 (92%) | 318 | 227 (71%) |