Table 2

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

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)


* Increase in overall retention with the addition of respondents from the RCT with initial non-responders

** RCT of reminder letters

*** Retention rate of entire sample

Booker et al. BMC Public Health 2011 11:249   doi:10.1186/1471-2458-11-249

Open Data