Table 3 Monetary and non-monetary incentives

Deehan et al., 1997 [11]

£10 vs no incentive

3.14

2.37, 4.15

£5 vs no incentive

2.22

1.66, 2.98

£10 charity donation vs no incentive

1.20

0.85, 1.69

£5 charity donation vs no incentive

1.12

0.79, 1.57

Pooled (Deehan, 1997)

1.87

1.48, 2.36

Everett et al., 1997 [28]

$1bill vs no incentive

1.86

1.34, 2.57

Pooled

1.87

1.55, 2.26

Nonmonetary incentives

Baron et al., 2001 [29]

Lottery to win weekend trip vs No incentive

1.31

1.02, 1.70

McLaren and Shelley, 2000 [30]

Awareness of prize vs no awareness of prize

1.17

0.84, 1.61

Pit et al., 2013 [25]

Pen vs no incentive

1.85

0.91, 3.77

Robertson et al., 2005 [31]

AU$2 Lottery vs no incentive

1.78

1.23, 2.60

Pooled

1.39

1.15, 1.69

Large vs small incentives

Asch et al., 1998 [26]

US$5 vs US$2

1.83

1.43, 2.35

Deehan et al., 1997 [11]

£10 cash vs £5 cash

1.41

1.06,1.87

£10 charity donation vs $5

1.08

0.73,1.58

Thomson et al., 2004 [32]

Lottery to win a large prize (6 bottles of champagne) vs six chances to win one bottle

1.47

1.05, 2.08

Pooled

1.47

1.19,1.81

Prepaid vs promised incentives

James et al., 2011 [27]

US$25 prepaid vs US$25 promised

2.88

1.70, 4.89