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Table 2 Median meta-analytic retention rates for each retention strategy

From: Retention strategies in longitudinal cohort studies: a systematic review and meta-analysis

  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%
  1. All inferential analyses adjusted for study duration and number of waves
  2. na insufficient studies to perform meta-analysis
  3. N No. effect in analysis
  4. *p < .05
  5. **p < .01