Table 2.
Median meta-analytic retention rates for each retention strategy
| Studies using strategy | Studies not using strategy | Absolute Difference | P | I2 | |||
|---|---|---|---|---|---|---|---|
| N | Retention Rate (Lower CI - Upper CI) | N | Retention Rate (Lower CI - Upper CI) | ||||
| Reducing barriers to participation (Any vs None) | 109 | 0.81 (0.77–0.84) | 34 | 0.71 (0.62–0.78) | 0.10 | 0.01* | 99.87% |
| Adapt materials for mixed abilities (e.g., non-English speaking participants) | 4 | 0.74 (0.37–0.93) | 139 | 0.79 (0.75–0.82) | − 0.05 | 0.67 | 99.88% |
| Adjust inclusion criteria | 1 | na | |||||
| Adjust lab to be more home-like, less clinical | 2 | 0.81 (0.77–0.84) | 141 | 0.79 (0.75–0.82) | 0.02 | 0.84 | 99.89% |
| Advisory group | 2 | 0.68 (0.58–0.77) | 141 | 0.79 (0.75–0.82) | − 0.11 | 0.56 | 99.89% |
| Alternative method of data collection | 36 | 0.86 (0.78–0.92) | 107 | 0.76 (0.72–0.8) | 0.10 | 0.01** | 99.88% |
| Anonymity for participants | 1 | na | |||||
| Assistance with postage costs | 5 | 0.88 (0.73–0.95) | 138 | 0.79 (0.75–0.82) | 0.09 | 0.21 | 99.89% |
| Assistance with transport/parking/directions | 12 | 0.8 (0.73–0.86) | 131 | 0.79 (0.75–0.82) | 0.01 | 0.72 | 99.88% |
| Catering/refreshments | 10 | 0.87 (0.8–0.92) | 133 | 0.78 (0.74–0.82) | 0.09 | 0.13 | 99.88% |
| Child care | 3 | 0.68 (0.51–0.82) | 140 | 0.79 (0.75–0.82) | − 0.11 | 0.36 | 99.89% |
| Consistency in research staff | 11 | 0.87 (0.77–0.93) | 132 | 0.78 (0.74–0.82) | 0.09 | 0.09 | 99.88% |
| Partial data collected from proxy/data linkage | 27 | 0.81 (0.73–0.86) | 116 | 0.79 (0.74–0.82) | 0.02 | 0.42 | 99.88% |
| Adapt materials for different languages | 12 | 0.84 (0.72–0.92) | 131 | 0.78 (0.75–0.82) | 0.06 | 0.39 | 99.88% |
| Extended data collection window | 7 | 0.74 (0.54–0.88) | 136 | 0.79 (0.75–0.82) | − 0.05 | 0.52 | 99.88% |
| Flexibility from research team (e.g., hours called, scheduling) | 24 | 0.83 (0.76–0.89) | 119 | 0.78 (0.74–0.82) | 0.05 | 0.23 | 99.88% |
| Focus group on survey design | 2 | 0.72 (0.7–0.75) | 141 | 0.79 (0.75–0.82) | −0.07 | 0.93 | 99.89% |
| Hiring, training, and support of staff | 21 | 0.84 (0.77–0.9) | 122 | 0.78 (0.74–0.82) | 0.06 | 0.11 | 99.88% |
| Matching staff to participants, e.g., by language spoken, nature of questions | 2 | 0.94 (0.91–0.96) | 141 | 0.79 (0.75–0.82) | 0.15 | 0.14 | 99.88% |
| Minimising time between data collection points | 1 | na | |||||
| Pilot testing | 4 | 0.81 (0.63–0.91) | 139 | 0.79 (0.75–0.82) | 0.02 | 0.93 | 99.89% |
| Prioritising measures | 12 | 0.73 (0.6–0.82) | 131 | 0.8 (0.76–0.83) | −0.07 | 0.37 | 99.89% |
| Recruiting for long-term retention | 10 | 0.83 (0.67–0.92) | 133 | 0.79 (0.75–0.82) | 0.04 | 0.50 | 99.87% |
| Schedule two participants simultaneously - often family or friends | 2 | 0.76 (0.66–0.84) | 141 | 0.79 (0.75–0.82) | −0.03 | 0.92 | 99.89% |
| Simple, efficient procedure | 1 | na | |||||
| Site and home visits | 31 | 0.84 (0.78–0.88) | 112 | 0.77 (0.73–0.81) | 0.07 | 0.07 | 99.88% |
| Skip waves | 15 | 0.84 (0.75–0.9) | 128 | 0.78 (0.74–0.82) | 0.06 | 0.25 | 99.88% |
| Splitting data collection over multiple sessions | 2 | 0.79 (0.78–0.81) | 141 | 0.79 (0.75–0.82) | 0.00 | 0.90 | 99.89% |
| Survey design (e.g., order of survey items) | 3 | 0.77 (0.52–0.91) | 140 | 0.79 (0.75–0.82) | −0.02 | 0.88 | 99.88% |
| Toll-free project phone number | 5 | 0.75 (0.57–0.88) | 138 | 0.79 (0.75–0.82) | −0.04 | 0.75 | 99.89% |
| Creating a project community (Any vs None) | 59 | 0.80 (0.75–0.85) | 84 | 0.78 (0.73–0.82) | 0.02 | 0.48 | 99.88% |
| Advisory group | 2 | 0.68 (0.58–0.77) | 141 | 0.79 (0.75–0.82) | − 0.11 | 0.56 | 99.89% |
| Branding | 14 | 0.79 (0.65–0.89) | 129 | 0.79 (0.75–0.82) | 0.00 | 0.99 | 99.88% |
| Certificate of appreciation/completion | 2 | 0.83 (0.28–0.98) | 141 | 0.79 (0.75–0.82) | 0.04 | 0.82 | 99.88% |
| Champion participants | 1 | na | |||||
| Educating the community on research | 5 | 0.87 (0.7–0.95) | 138 | 0.79 (0.75–0.82) | 0.08 | 0.40 | 99.89% |
| Emphasising benefits of study | 3 | 0.82 (0.7–0.9) | 140 | 0.79 (0.75–0.82) | 0.03 | 0.79 | 99.89% |
| Events/opportunity to meet other participants | 9 | 0.69 (0.54–0.82) | 134 | 0.8 (0.76–0.83) | −0.11 | 0.23 | 99.88% |
| Feedback report | 10 | 0.84 (0.73–0.91) | 133 | 0.79 (0.75–0.82) | 0.05 | 0.39 | 99.88% |
| Gaining support of relevant institutions and organisations | 4 | 0.85 (0.71–0.93) | 139 | 0.79 (0.75–0.82) | 0.06 | 0.57 | 99.89% |
| Gift/ freebies | 19 | 0.8 (0.67–0.88) | 124 | 0.79 (0.75–0.82) | 0.01 | 0.90 | 99.89% |
| Hiring, training, and support of staff | 21 | 0.84 (0.77–0.9) | 122 | 0.78 (0.74–0.82) | 0.06 | 0.11 | 99.88% |
| Letter from chief investigator | 1 | na | |||||
| Media coverage | 3 | 0.7 (0.69–0.72) | 140 | 0.79 (0.75–0.82) | −0.09 | 0.82 | 99.89% |
| Newsletter/e-newsletter | 24 | 0.83 (0.76–0.89) | 119 | 0.78 (0.74–0.82) | 0.05 | 0.23 | 99.88% |
| Opportunity to participate in other research | 1 | na | |||||
| Photo album | 2 | 0.72 (0.69–0.75) | 141 | 0.79 (0.75–0.82) | −0.07 | 0.75 | 99.89% |
| Building rapport | 22 | 0.79 (0.69–0.86) | 121 | 0.79 (0.75–0.82) | 0.00 | 0.97 | 99.89% |
| Sharing study results | 5 | 0.88 (0.66–0.97) | 138 | 0.79 (0.75–0.82) | 0.09 | 0.24 | 99.89% |
| Social media | 2 | 0.89 (0.72–0.96) | 141 | 0.79 (0.75–0.82) | 0.10 | 0.39 | 99.89% |
| Study membership card | 1 | na | |||||
| Thank you, birthday, and holiday cards | 25 | 0.85 (0.79–0.9) | 118 | 0.78 (0.73–0.81) | 0.07 | 0.07 | 99.88% |
| Time with chief investigator | 2 | 0.92 (0.8–0.97) | 141 | 0.79 (0.75–0.82) | 0.13 | 0.24 | 99.89% |
| Website | 3 | 0.80 (0.47–0.94) | 140 | 0.79 (0.75–0.82) | 0.01 | 1.00 | 99.88% |
| Follow-up/Reminder strategies (Any vs None) | 111 | 0.76 (0.72–0.80) | 32 | 0.86 (0.79–0.91) | −0.10 | 0.02* | 99.86% |
| Follow-up brochure | 2 | 0.78 (0.74–0.81) | 141 | 0.79 (0.75–0.82) | − 0.01 | 0.97 | 99.89% |
| Budgeting for multiple contact attempts | 1 | na | |||||
| Extra incentive to complete all data collection points | 2 | 0.93 (0.77–0.98) | 141 | 0.79 (0.75–0.82) | 0.14 | 0.17 | 99.89% |
| Gift/ freebies incentives (e.g., t-shirts, discount cards) | 18 | 0.8 (0.67–0.88) | 125 | 0.79 (0.75–0.82) | 0.01 | 0.90 | 99.89% |
| Hiring, training, and support of staff | 21 | 0.84 (0.77–0.9) | 122 | 0.78 (0.74–0.82) | 0.06 | 0.11 | 99.88% |
| Incentive (cash/vouchers) | 59 | 0.78 (0.72–0.82) | 84 | 0.8 (0.75–0.84) | −0.02 | 0.45 | 99.88% |
| Incentive increasing value over time | 10 | 0.78 (0.62–0.88) | 133 | 0.79 (0.75–0.82) | − 0.01 | 0.81 | 99.88% |
| Incentives raffles/competitions | 11 | 0.86 (0.71–0.94) | 132 | 0.78 (0.75–0.82) | 0.08 | 0.22 | 99.88% |
| Increased incentive for hard-to-reach Pp | 6 | 0.68 (0.47–0.84) | 137 | 0.79 (0.76–0.83) | −0.11 | 0.24 | 99.88% |
| Limiting number of calls etc. based on participants’ response | 1 | na | |||||
| Medical assistance (e.g., diagnostic testing) | 27 | 0.74 (0.64–0.82) | 116 | 0.8 (0.76–0.84) | −0.06 | 0.17 | 99.88% |
| Phone Follow-up | 11 | 0.80 (0.67–0.89) | 132 | 0.79 (0.75–0.82) | 0.01 | 0.90 | 99.88% |
| Provide referrals, e.g., medical or legal | 9 | 0.85 (0.77–0.91) | 134 | 0.78 (0.75–0.82) | 0.07 | 0.26 | 99.89% |
| Resend survey once | 6 | 0.77 (0.64–0.86) | 137 | 0.79 (0.75–0.82) | −0.02 | 0.79 | 99.88% |
| Resend survey multiple times | 10 | 0.76 (0.64–0.84) | 133 | 0.79 (0.75–0.83) | −0.03 | 0.63 | 99.88% |
| SMS follow-up | 1 | na | |||||
| Website follow-up | 8 | 0.81 (0.62–0.91) | 135 | 0.79 (0.75–0.82) | 0.02 | 0.93 | 99.88% |
| Email reminder | 13 | 0.73 (0.58–0.85) | 130 | 0.79 (0.76–0.83) | −0.06 | 0.31 | 99.88% |
| Face-to-face reminder (e.g., home visit) | 7 | 0.85 (0.67–0.94) | 136 | 0.79 (0.75–0.82) | 0.06 | 0.33 | 99.89% |
| Phone call reminder | 34 | 0.73 (0.63–0.8) | 109 | 0.81 (0.77–0.84) | −0.08 | 0.05* | 99.88% |
| Postcard/letter reminder | 43 | 0.77 (0.7–0.83) | 100 | 0.80 (0.75–0.84) | −0.03 | 0.50 | 99.88% |
| SMS reminder | 5 | 0.85 (0.8–0.9) | 138 | 0.79 (0.75–0.82) | 0.06 | 0.42 | 99.89% |
| Reminders (unspecified) | 1 | na | |||||
| Tracing strategies (Any vs None) | 53 | 0.80 (0.73–0.85) | 90 | 0.78 (0.74–0.83) | 0.02 | 0.62 | 99.88% |
| Tracing via alternative contacts | 28 | 0.82 (0.75–0.87) | 115 | 0.78 (0.74–0.82) | 0.04 | 0.32 | 99.88% |
| Case-review meetings | 1 | na | |||||
| Tracing via change of address cards | 2 | 0.74 (0.43–0.91) | 141 | 0.79 (0.75–0.82) | −0.05 | 0.95 | 99.89% |
| Tracing via email | 2 | 0.74 (0.43–0.92) | 141 | 0.79 (0.75–0.82) | −0.05 | 0.82 | 99.89% |
| Extensive location tracking information, e.g., known ‘hangouts’ | 1 | na | |||||
| Hiring, training, and support of staff | 21 | 0.84 (0.77–0.9) | 122 | 0.78 (0.74–0.82) | 0.06 | 0.11 | 99.88% |
| Tracing via house visit | 1 | na | |||||
| Tracing via incentive for staff members | 2 | 0.72 (0.67–0.76) | 141 | 0.79 (0.75–0.82) | −0.07 | 0.69 | 99.89% |
| Tracing via incentive to update contact details | 3 | 0.86 (0.62–0.96) | 140 | 0.79 (0.75–0.82) | 0.07 | 0.43 | 99.88% |
| Tracing via letter | 9 | 0.77 (0.51–0.91) | 134 | 0.79 (0.75–0.82) | −0.02 | 0.72 | 99.89% |
| Tracing via locator form documentation* | 7 | 0.91 (0.79–0.97) | 136 | 0.78 (0.74–0.81) | 0.13 | 0.02* | 99.88% |
| Tracing via phone call | 8 | 0.67 (0.51–0.8) | 135 | 0.8 (0.76–0.83) | −0.13 | 0.12 | 99.88% |
| Tracing via private investigator | 1 | na | |||||
| Tracing via SMS | 1 | na | |||||
| Tracing via social media | 3 | 0.79 (0.39–0.95) | 140 | 0.79 (0.75–0.82) | 0.00 | 0.92 | 99.89% |
| Tracing via tracing via public records | 20 | 0.82 (0.73–0.88) | 123 | 0.78 (0.74–0.82) | 0.04 | 0.37 | 99.88% |
| Tracing via tracking database | 15 | 0.83 (0.73–0.9) | 128 | 0.78 (0.74–0.82) | 0.05 | 0.32 | 99.88% |
| Tracing via update your details form | 4 | 0.9 (0.81–0.96) | 139 | 0.79 (0.75–0.82) | 0.11 | 0.15 | 99.89% |
| Tracing via website | 2 | 0.80 (0.79–0.81) | 141 | 0.79 (0.75–0.82) | 0.01 | 0.99 | 99.89% |
| Tracing via non-public records, e.g., apartment complex managers | 7 | 0.82 (0.66–0.92) | 136 | 0.79 (0.75–0.82) | 0.03 | 0.59 | 99.89% |
All inferential analyses adjusted for study duration and number of waves
na insufficient studies to perform meta-analysis
N No. effect in analysis
*p < .05
**p < .01