From: Effect of reminders on mitigating participation bias in a case-control study
 | Group | 1A | 1B | 1C |  |
---|---|---|---|---|---|
 |  | First mailing | First reminder | Second reminder | Total§ |
Sex | Female | 56.0% | 49.5% | 51.9% | 53.3% |
χ 2 p = 0.004 | Male | 44.0% | 50.5% | 48.1% | 45.2% |
 | Total | 2507 | 703 | 717 | 3927 |
Age group | 18-24 | 5.4% | 6.0% | 10.3% | 6.3% |
χ 2 p < 0.001 | 25-34 | 12.6% | 13.1% | 14.8% | 12.9% |
 | 35-44 | 19.0% | 20.5% | 24.7% | 20.0% |
 | 45-54 | 20.0% | 21.2% | 20.8% | 20.1% |
 | 55-64 | 20.0% | 19.2% | 15.1% | 18.7% |
 | 65+ | 23.1% | 20.1% | 14.4% | 20.7% |
 | Total | 2507 | 703 | 717 | 3927 |
Age at leaving full-time education | < 16 yrs | 28.3% | 30.9% | 26.1% | 28.3% |
χ 2 p = 0.007 | 16 yrs | 29.4% | 29.3% | 34.6% | 30.4% |
 | 17 yrs | 9.0% | 9.5% | 8.8% | 9.0% |
 | 18 yrs | 11.5% | 9.1% | 10.3% | 10.9% |
 | 19 yrs | 20.5% | 19.2% | 17.1% | 19.6% |
 | Still in education | 1.3% | 1.9% | 3.1% | 1.8% |
 | Total †| 2463 | 692 | 706 | 3861 |
IMD quintile | 1 (most deprived) | 15.2% | 18.4% | 19.0% | 16.5% |
χ 2 p = 0.056 | 2 | 16.0% | 14.8% | 18.6% | 16.2% |
 | 3 | 20.3% | 18.8% | 19.0% | 19.8% |
 | 4 | 22.5% | 21.2% | 19.0% | 21.6% |
 | 5 | 26.0% | 26.8% | 24.4% | 25.9% |
 | Total ‡ | 2483 | 697 | 710 | 3890 |