3. Participants (Category B).
| Sub‐domains | Study ID | Intervention | Control |
| 10B. Reminders: electronic reminder vs usual follow‐up | |||
| Ashby 2011 | Additional electronic reminder in follow‐up | Usual follow‐up | |
| Starr 2015 (Email reminder) | Email reminder | Postal email reminder | |
| Starr 2015 (SMS text pre‐notification) | Prenotification reminder | Usual follow‐up | |
| 11B. Reminders: action oriented electronic reminder vs standard electronic reminder | |||
| Edwards 2016 (photo trial) | The personalised photo on the letter | Usual letter | |
| Edwards 2016 (pre‐call trial) | Active reminder | Usual reminder | |
| 12B. Reminders: personalised reminder vs non‐personalised reminder | |||
| Nakash2007 | Calendar | Usual follow‐up | |
| Bradshaw 2020 | Intervention group 1 received an SMS message the day before the email with the link to the questionnaire. | No SMS | |
| 13B. Reminders: telephone reminder vs usual follow‐up | |||
| Severi 2011 | Telephone call reminder | Usual follow‐up | |
| 14B. Reminders: telephone reminder vs postal reminder | |||
| Tai 1997 | Telephone reminder | Postal reminder | |
| 15B. Prompts: electronic prompt vs no prompt | |||
| Bradshaw 2020 | Intervention group 1 received an SMS message and a further £10 high‐street shopping voucher sent by post before the 24 months visit. Intervention group 2 received a further £10 high‐street shopping voucher given at the visit. |
No voucher | |
| Clark 2015 | Received an SMS or e‐mail to return a study questionnaire | Received no electronic prompt to returns a study questionnaire | |
| Keding 2016 | Text message prompt Prompt Reminder |
Usual follow‐up Reminder Usual follow‐up |
|
| Man 2011 | Electronic reminder | No reminder | |
| Starr 2015 (Email reminder) | Email reminder | Postal email reminder | |
| Starr 2015 (SMS text pre‐notification) | Prenotification reminder | Usual follow‐up | |
| 16B. Prompts: telephone prompt vs usual follow‐up | |||
| Edwards 2016 (Email trial) | Addition of an email as prompt | Usual Follow‐up | |
| MacLennan 2014 | Received a telephone call from the trial office ahead of the reminder questionnaire in addition to the usual reminder schedule | Received the usual reminder schedule only | |
| 17B. Prompts: Prenotification card vs no card | |||
| Treweek 2020a | Pre‐notification card sent around 1 month before | No pre‐notification card | |
| 18B. Prompts: sticker vs no sticker | |||
| Goulao 2020 | Received a logo sticker on questionnaire envelopes | Received no sticker | |
| 19B. Prompts: personalised prompt vs no prompt | |||
| Cochrane 2020 | Personalised reminder | Non‐personalised reminder | |
| Mitchell 2020 | Personalised text message | No personalised text message | |
| Nakash 2007 | Calendar | Usual follow‐up | |
| 20B. Monetary incentives: addition of monetary incentives vs usual follow‐up | |||
| Bauer 2004 | Interventions group 1 received an incentive of US$10 Interventions group 2 received an incentive of US$2 |
Received no incentive | |
| Gates 2009 | £5 gift voucher | Received no gift voucher | |
| Kenyon 2005 | Monetary incentive (£5 voucher) | No incentive | |
| 21B. Monetary incentives: addition of monetary incentives to all trial arms | |||
| Bauer 2004 | Interventions group 1 received an incentive of US$10 Interventions group 2 received an incentive of US$2 |
Received no incentive | |
| Bradshaw 2020 | Intervention group 1 received an SMS message and a further £10 high‐street shopping voucher sent by post before the 24‐month visit. Intervention group 2 received a further £10 high‐street shopping voucher given at the visit. |
No voucher | |
| 22B. Monetary incentives: addition of monetary incentives vs addition of monetary reward | |||
| Bradshaw 2020 | Intervention group 1 received an SMS message and a further £10 high‐street shopping voucher sent by post before the 24 months visit. Intervention group 2 received a further £10 high‐street shopping voucher given at the visit. |
No voucher | |
| Cook 2020 | £20 gift voucher given to study at the end of the recruitment visit | A conditional offer of monetary incentive | |
| Dorling 2020 | Received the first paper letter to parents included a promise of an incentive (£15 gift voucher redeemable at some shops) after receipt of a completed form. | Received the first paper letter to parents would enclose the incentive (£15 gift voucher redeemable at high‐street shops) before the receipt of a completed form | |
| Young 2020 | Addition of monetary incentive (£5 multistore voucher) | An offer of incentive (i.e. Conditional vs unconditional £5 multistore voucher) | |
| 23B. Monetary incentives: addition of monetary reward vs usual follow‐up | |||
| Marsh 1999 (Clinic trial) | Clinic visit with an incentive (£2 voucher) | Clinic visit without incentive | |
| Marsh 1999 (Postal trial) | Postal follow‐up with incentive (£2 voucher) | Postal follow‐up without incentive | |
| Marsh 1999 (Telephone trail) | Telephone follow‐up with incentive (£2 voucher) | Telephone follow‐up without incentive | |
| Watson 2017 |
Intervention group 1 received unconditional (£5 gift voucher) at 12 but not 24 months. Intervention group 2 received unconditional (£5 gift voucher) at 12 and 24 months. Intervention group 3 received unconditional (£5 gift voucher) at 24 but not 12 months. |
No voucher | |
| Arundel 2019 | An offer of conditional monetary incentive (£10 cash reliant on providing in addition to the £10 gift voucher routinely provided) | Usual follow‐up (£10 gift voucher routinely provided) | |
| 24B. Monetary incentives: addition of monetary rewards to all trial arms | |||
| Hardy 2016 | An offer of conditional monetary incentive (£10 gift voucher) | Later offer of conditional monetary incentive (£10 gift voucher) | |
| 25B. Monetary incentives: addition of monetary incentives vs lottery | |||
| Kenton 2007 | Monetary incentive (CAN$2 coin mailed with the questionnaire or draw for a CAN$50 gift certificate upon questionnaire receipt) | Lottery | |
| 26B. Monetary incentives: lottery vs usual follow‐up | |||
| No incentive | |||
| 27B. Monetary incentives: addition of lottery to both trial arms | |||
| Henderson 2010 | An offer of winning voucher (winning 1 of 25 £20 shopping vouchers or winning one £500 shopping voucher) | No incentive | |
| 28B. Non‐monetary incentives: addition of pen vs usual follow‐up | |||
| Bell 2016 | Addition of a pen | No pen | |
| Cunningham‐Burley 2020 | Branded pen with their questionnaire | No pen | |
| James 2020 | Pen with trial invitation pack | No pen | |
| Mitchell 2020b | Addition of a pen | No pen | |
| Sharp 2006 | Pen | No pen | |
| 29B. Non‐monetary incentives: addition of societal benefit message vs usual follow‐up | |||
| Severi 2011 | Fridge magnet and benefit to society message | Usual follow‐up | |
| 30B. Non‐monetary incentives: certificate of appreciation vs usual follow‐up | |||
| Renfroe 2002 | Timing of postal questionnaire, cover letter signatory, express mail | Regular mail and non‐monetary incentive. | |
| 31B. Maintaining participant engagement: newsletter vs usual follow‐up | |||
| Goulao 2020 | Received a tested a theoretically informed newsletter sent before the questionnaire | Received no newsletter | |
| MARMOTH trial | Newsletter one month before the 24‐month paper follow‐up questionnaire | No newsletter | |
| Mitchell 2012 | Invitation mailing packs with a white envelope | Invitation mailing packs with a brown envelope | |
| Rodgers 2019 | Newsletter + handwritten posit it notes Newsletter + printed posit it notes Newsletter only Handwritten posit it notes only Printed posit it note only |
Usual follow‐up | |
| 32B. Maintaining participant engagement: offer of receiving trial results vs usual follow‐up | |||
| Cockayne 2005 | Offered the result of the trial in a questionnaire | No offer of knowing the results | |
| 33B. Maintaining participant engagement: cover letter including a social incentive vs standard cover letter | |||
| James 2020 |
Intervention group 1 received a branded pen and a standard cover letter. Intervention group 2 received a branded pen and a social incentive cover letter. Intervention group 3 received no pen and a social incentive cover letter. |
Control group received no pen, standard cover letter. | |
| 34B. Maintaining participant engagement: personalised cover letter vs usual cover letter | |||
| Edwards 2016 (Email trial) | Addition of an email as prompt | Usual follow‐up | |
| Edwards 2016 (photo trial) | Personalised photo on the letter | Usual letter | |
| Edwards 2016 (pre‐call trial) | Active reminder | Usual reminder | |
| 35B. Maintaining participant engagement: varying signatory on cover letter | |||
| Renfroe 2002 | Timing of postal questionnaire, cover letter signatory, express mail | Regular mail and non‐monetary incentive. | |
| 36B. Maintaining participant engagement: addition of a deadline vs usual follow‐up | |||
| Gatellari 2004 | Cover letter advising return within 1‐week | Standard cover letter | |
| 37B. Maintaining participant engagement: addition of an estimate of time to complete vs no addition | |||
| Marson 2007 | Cover letter though post with the questionnaire that included an estimate of the length of time that it may take to complete | Standard cover letter with no indication of length of time required | |
| 38B. Maintaining participant engagement: brown vs white envelope | |||
| Mitchell 2011 | Invitation mailing packs with a white envelope | Invitation mailing packs with a brown envelope | |
| 39B. Maintaining participant engagement: post‐it notes vs usual follow‐up | |||
| Lewis 2017 | Addition of a post‐it note | Usual follow‐up | |
| Rodgers 2019 | Newsletter + handwritten posit it notes Newsletter + printed posit it notes Newsletter only Handwritten posit it notes only Printed posit it note only |
Usual follow‐up | |
| Tilbrook 2015 | Addition of a post‐it note | Usual follow‐up | |
| 40B. Maintaining participant engagement: inclusion of trial newspaper article vs usual follow‐up | |||
| Salvesen 1992 | Newspaper article | Usual follow‐up | |
| 41B. Maintaining participant engagement: frequency of telephone contact | |||
| Glassman 2020 | Received telephone calls at baseline, six months, and at annual visits after that (annual contact) | Received a call at baseline only (baseline contact) | |
| 42B. Maintaining participant engagement: request for collateral (concomitant) | |||
| Cunningham 2004 |
Intervention group1 were asked to provide a collateral. Intervention group2 asked to provide collateral and told that there was a 50% chance that the collateral would be contacted. All those respondents asked for collateral were told that the collateral would receive a CAN$20 payment for a brief telephone interview. |
Not asked to provide a collateral | |
| 43B. Behavioural interventions: theory informed cover letter vs usual cover letter | |||
| AMBER trial | Received a tested a theoretically informed letter sent with the questionnaire | Received a standard letter | |
| Goulao 2020 | Theory informed letter to follow‐up | Usual letter follow‐up | |
| Goulao 2020 (replication) | Theory informed letter to follow‐up | Usual letter follow‐up | |
| OPAL trial | Received a tested a theoretically informed letter sent with the questionnaire | Received a standard letter | |
| 44B. Behavioural interventions: motivational interviewing vs usual follow‐up | |||
| Bean 2018 | Theory informed to follow‐up | Usual follow‐up | |