Table 1 Sample size, the wording of the additional sentence and response rate overall and in the 11 treatment groups (1 control group and 10 intervention groups)
Treatment group | Wording of the sentence | Response rate (%) | OR | 95% CI | |
|---|---|---|---|---|---|
Control group (treatment group 1/generic letter) (n = 4,000) | – | 57.7 | Ref | ||
Intervention group (treatment group 2/specific letter) (n = 2,100) | The questionnaire will address themes such as stress, alcohol and sleep problems. | 56.8 | 0.96 | (0.87–1.07) | p = 0.493 |
Intervention group (treatment group 3/specific letter) (n = 2,100) | The questionnaire will address themes such as stress, alcohol and contact with family and friends. | 57.8 | 1.00 | (0.90–1.12) | P = 0.948 |
Intervention group (treatment group 4/specific letter) (n = 2,100) | The questionnaire will address themes such as stress, alcohol and sex | 55.6 | 0.92 | (0.83–1.02) | P = 0.123 |
Intervention group (treatment group 5/specific letter) (n = 2,100) | The questionnaire will address themes such as stress, sleep problems and contact with family and friends. | 55.8 | 0.93 | (0.83–1.03) | P = 0.151 |
Intervention group (treatment group 6/specific letter) (n = 2,100) | The questionnaire will address themes such as stress, sleep problems and sex. | 54.8 | 0.89 | (0.80–0.99) | P = 0.029 |
Intervention group (treatment group 7/specific letter) (n = 2,100) | The questionnaire will address themes such as stress, sex and contact with family and friends. | 56.5 | 0.95 | (0.86–1.06) | p = 0.368 |
Intervention group (treatment group 8/specific letter) (n = 2,100) | The questionnaire will address themes such as sex, sleep problems and contact with family and friends. | 53.4 | 0.84 | (0.76–0.93) | p = 0.001 |
Intervention group (treatment group 9/specific letter) (n = 2,100) | The questionnaire will address themes such as sex, alcohol and contact with family and friends. | 54.8 | 0.89 | (0.80–0.99) | p = 0.032 |
Intervention group (treatment group 10/specific letter) (n = 2,100) | The questionnaire will address themes such as sex, sleep problems and alcohol. | 55.8 | 0.93 | (0.83–1.03) | P = 0.161 |
Intervention group (treatment group 11/specific letter) (n = 2,100) | The questionnaire will address themes such as alcohol, sleep problems and contact with family and friends. | 56.7 | 0.96 | (0.86–1.07) | P = 0.471 |