Table 1 Characteristics of included studies
Study ID | Year | Country | Clinical population | Timing of follow up | Retention intervention | Timing of retention intervention | Target behaviour | Sample size | Effect size | Explicit use of theory in development? |
|---|---|---|---|---|---|---|---|---|---|---|
Electronic prompts | ||||||||||
Ashby [10] | 2011 | UK | Food sensitivity for prevention of migraine | 4 week follow up | Electronic prompt: SMS/email/both | Coincide with receipt of questionnaire | Return of postal questionnaire | 148 | 5.4% (95% CI 4.6, 15.4) | No |
Clark [4] | 2015 | UK | Identifying individuals with chronic obstructive pulmonary disease | Between 2 and 6 months (dependent on site) | Electronic prompt: SMS/email/both | Coincide with receipt of questionnaire—‘2 days after the questionnaire was sent’ | Return of postal questionnaire | 437 | 8.8% (95% CI 0.11, 17.7) | No |
Man [11] | 2011 | UK | Yoga for treatment of lower back pain | 6 months | Electronic prompt: SMS/email | Coincide with receipt of questionnaire—‘on the day that participants were due to receive their questionnaire’ | Return of postal questionnaire | 125 | 3% (95% CI 10, 16) | No |
Monetary incentives | ||||||||||
Bauer [6] | 2003 | USA | Community intervention trial for smoking cessation | 2 weeks | Monetary incentive (cheque for $10 USD or $2 USD) | At time of data collection, i.e. unconditional | Sample collection kits and return of postal questionnaire | 300 | OR = 1.66 (95% CI 0.83,3.33) | No |
Gates [7] | 2009 | UK | Managing acute whiplash injuries in emergency departments | 4 months and 8 months | Monetary incentive (£5 GBP voucher) | At time of data collection—4 months or 8 months, i.e. unconditional | Return of postal questionnaire | 2144 | RR 1.10 (95% CI 1.05, 1.16) | No |
Kenyon [8] | 2005 | UK | Use of antibiotics to improve neonatal outcomes in preterm labour or preterm rupture of membranes—long term follow up | 7 years post trial contact is initiated by letter. Questionnaire sent at 2 weeks | Monetary reward (£5 GBP voucher) | 6 weeks post first questionnaire with reminder, i.e. unconditional | Return of postal questionnaire | 722 | 11.7% (95% CI 4.7, 18.6) | No |
Khadjesari [9] | 2011 | UK | Reducing alcohol levels amongst problem drinkers | Study 1: 3 months Study 2: 12 months | Study 1: Monetary incentive 1. £5 Amazon voucher 2. £ 5 charitable donation 3. £250 prize draw Study 2: Monetary incentive (£10 Amazon voucher) | Study 1: promise of incentive within 1 week of questionnaire, i.e. conditional Study 2: promise of incentive at each email reminder, i.e. conditional | Return of online questionnaire—linked in email | Study 1: 1226 Study 2: 2591 | Study 1: 2% (95% CI −3, 7) Study 2: 9% (95% CI 5. 12) | No |