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Table 2 Increase in Study Retention Rates for Incentive and Reminder Letters by Data Collection Type

From: A systematic review of the effect of retention methods in population-based cohort studies

  

Data Collection Method

 

Postal

Face-to-Face

Telephone

Mixed

Evaluated Retention Method, reference number

Average increase in retention rate, proportion (95% CI)

Average increase in retention rate, proportion (95% CI)

Average increase in retention rate, proportion (95% CI)

Average increase in retention rate, proportion (95% CI)

Incentives

    

RCT - Financial Only

    

Doody[22]*

0.01 (0.01, 0.01)

   

Olsen (NLS79)[27–30]*

   

0.05 (0.05, 0.06)

Olsen (NLSW)[27–30]*

   

0.02 (0.02, 0.03)

Laurie[25, 26]***

 

0.85 (0.84, 0.85)

  

Rodgers[32]***

  

0.80 (0.87, 0.88)

 

RCT - Gift Only

    

Kalsbeek[23]***

  

0.78 (0.76, 0.79)

 

White[33]*

0.11 (0.01, 0.14)

   

RCT - Mixed

    

Olsen (NLS97)[27–30]*

 

0.28 (0.27, 0.29)

  

Non-RCT - Gift Only

    

Hoffman[40]

0.47 (0.44, 0.49)

   

Non-RCT - Mixed

    

Rudy [45]***

0.72 (0.65, 0.79)

   

Reminder Letters

    

1 Letter Posted

    

Boys[34]

0.12 (0.10, 0.15)

   

Hoffman[40]

0.02 (0.02, 0.03)

   

Koo[24]**

0.32 (0.29, 0.36)

   

Russell[46]

0.03 (0.03, 0.03)

   

2 Letters Posted

    

Clarke[36]

0.18 (0.15, 0.22)

   

Eagan[37]

0.18 (0.17, 0.19)

   

Walker[49]

0.18 (0.17, 0.19)

   

WHA Research Group (YC)[50–53]

0.03 (0.03, 0.03)

   

WHA Research Group (MC)[50–53]

0.10 (0.10, 0.11)

   

WHA Research Group (OC)[50–53]

0.46 (0.45, 0.47)

   

3 Letters Posted

    

Ullman[48]

0.23 (0.20, 0.26)

   
  1. * Increase in overall retention with the addition of respondents from the RCT with initial non-responders
  2. ** RCT of reminder letters
  3. *** Retention rate of entire sample