1. Some investigators (see, e.g., Presser, 1989) recommend attempting to interview in later waves the nonrespondents to an earlier wave, but often this is not done. Even when it is, cooperation on a subsequent wave is generally predicted by prior cooperation.
2. For evidence concerning interviewer expectation effects, see Hyman (1954); Sudman et al. (1977); Singer and Kohnke-Aguirre (1979); Singer et al. (1983); and Hox (1999). Lynn (1999) reports an experiment in which interviewers believed respondents who had received an incentive responded at a lower rate, whereas their response rate was in fact significantly higher than those who received no incentive. However, these interviewer beliefs were measured after, rather than before, the survey.
3. They used the multinomial logit specification in CATMOD, which allows researchers to perform modeling of data that can be represented by a contingency table. CATMOD fits linear models to functions of response frequencies and can use linear modeling, log-linear modeling, logistic regression, and repeated measurement analysis. A more complete description can be found in: SAS Institute Inc., 1989, SAS/STAT Users Guide, Version 6, Fourth Edition, Volume 1, Cary, NC: SAS Institute Inc.
4. These counts are based on the bivariate distributions, without controls for demographic characteristics. The effects do not disappear with such controls; indeed, three additional variables show such effects with demographic controls.
5. To our knowledge, however, no high-quality studies are available yet that explore potential differences in the effectiveness of incentives by ethnicity or language per se.
6. However, Sundukchi (1999) reports that an incentive paid in Wave 7 to all low-income households that had received an incentive in Wave 1 reduced the nonresponse rate among nonblack low-income households, but not among black low-income households.
7. In that study, all nonrespondents were sent the incentive offer by FedEx mail; hence, it was not possible to separate the effect of the monetary incentive from the special mailing. In a subsequent small-scale experiment, money had a significant effect on converting refusals, whereas a FedEx mailing did not (Daniel Hill, personal communication n.d.).
8. Shettle and Mooney (1999) conclude that the incentive does not reduce nonresponse bias in their study. It is true that after extensive followups, there is no difference at all between the incentive and the no-incentive groups. Nevertheless, the trends prior to phone followup are in the expected direction.
9. The finding that respondent beliefs about survey organization practices are affected by their own experience parallels findings reported elsewhere (Singer et al. 1998c). In that Singer et al. study, 31 percent of respondents to the Survey of Consumer Attitudes who had not been offered any incentives 6 months earlier said, in 1997, that respondents should get paid for participating in that type of survey; 51 percent of those offered $5 said, 6 months later, that they thought respondents should get paid; and 77 percent of respondents who received $20 or $25 as a refusal conversion payment said respondents should get paid.
10. However, as we would expect, the perception of fairness is directly and significantly related to whether or not respondents had themselves received a refusal conversion payment. Among those who did not receive such a payment, 74.5 percent (of 200) considered this practice unfair. Among those who did receive a refusal conversion payment, only 55 percent (of 20) considered the practice unfair; this difference is significant at the .06 level.
11. This discussion is based on unpoublished analyses by Van Hoewyk, Singer, and Couper of data from the Survey of Consumer Attitudes during 8 months in 1998.
12. Such inconsistencies are not largely due to differences in sample sizes, that is an inability to detect significant differences between incentive and nonincentive groups (or other relevant comparisons) because the sample sizes in these studies were too low. Sample sizes were provided for each of the studies cited in their original reports. Although we have not repeated them here, they were, with very few exceptions, adequate to detect reasonable expected differences between experimental groups.