“…In a nutshell, available research convincingly shows that (1) incentives increase response rates, irrespective of the survey mode used, (2) unconditional (prepaid) incentives are more effective than conditional (promised) incentives, (3) monetary incentives are more effective than vouchers and in-kind incentives, and (4) the higher value of an incentive, the stronger is the effect it produces, albeit marginal returns diminish (Singer & Ye, 2013). More recently, researchers have also started enquiring the effect of incentives on indicators of response quality, notably on item nonresponse (Curtin, Singer, & Presser, 2007;Davern, Rockwood, Sherrod, & Campbell, 2003;Medway, 2012).…”