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Many researchers have examined the effect of providing
a variety of nonmonetary incentives to subjects. These
include token gifts such as small packages of coffee,
ball-point pens, postage stamps, key rings, trading
stamps, participation in a raffle or lottery, or a
donation to a charity in the respondent's name. Generally
(although not consistently), nonmonetary incentives have
resulted in an increased response. A meta-analysis of 38
studies that used some form of an incentive revealed that
monetary and nonmonetary incentives were effective only
when enclosed with the survey. The promise of an
incentive for a returned questionnaire was not effective
in increasing response. The average increase in response
rate for monetary and nonmonetary incentives was 19.1
percent and 7.9 percent, respectively.
Most researchers have found that higher monetary
incentives generally work better than smaller ones. One
researcher proposed a diminishing return model, where
increasing the amount of the incentive would have a
decreasing effect on response rate. A meta-analysis of
fifteen studies showed that an incentive of 25¢
increased the response rate by an average of 16 percent,
and $1 increased the response by 31 percent.
Offering a copy of the final report has proved to be a good incentive
when respondents are actively involved in the subject of the survey..
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