The Impact of Survey Incentive Amounts on Response Rates and 

Estimates of Sexual Assault Victimization 

Christopher Krebs1, Christine Lindquist1, Ashley Richards1, Bonnie Shook-Sa1, Marcus 

Berzofsky1, Kimberly Peterson1, Michael Planty2, Lynn Langton2, Jessica Stroop2 

1. RTI International, 3040 Cornwallis Road, Research Triangle Park, NC 27709 

2. Bureau of Justice Statistics, 810 Seventh Street NW, Washington, DC 20531

Abstract 

Survey incentives have proven to increase response rates in web surveys, but little is known about if or how 

incentives impact responses to sensitive survey questions and the estimates researchers derive. To evaluate the 

potential impact of incentives on response rates and estimates derived from sensitive items, we conducted an 

experiment to compare the effects of incentives of different monetary amounts in a survey on an extremely sensitive 

topic: sexual assault victimization. Bivariate analyses were used to determine whether larger incentives ($25 vs. $10; 

and $40 vs. $25) yielded significantly higher response rates (by sex) and whether victimization estimates differed by 

incentive amounts. Bivariate analyses indicate that $25 increased response rates over $10 for female and male 

students, but $40 did not increase response rates over $25 for female or male students. In terms of victimization, 

offering both $10 and $40 were associated significantly higher sexual assault victimization rates than offering $25 

for female students. Modeled results, controlling for student characteristics produce mixed results. 

Introduction 

As part of the Campus Climate Survey Validation Study (CCSVS) Pilot Test (Krebs et al., 2016) which aimed to 

develop a valid and reliable methodology for campus climate surveys, we conducted an experiment intended to 

guide recommendations regarding incentive amounts for future efforts. The experiment compared the impact of 

different survey amounts ($25 vs. $10; and $40 vs. $25). The purpose of the experiment was to determine the 

optimal incentive amount for encourage survey response without impacting victimization rates. Although larger 

incentives have been found to lead to higher response rates, the returns tend to diminish (Cantor, O’Hare, & 

O’Connor, 2008). Additionally, the impact of a particular incentive amount depends on characteristics of the survey 

and sample, so an incentive amount that is effective for one survey may not be equally effective for another survey. 

Although survey incentives have proven to increase response rates in web surveys, less is known about the impact 

that different incentive amounts have on estimates derived from data collected via survey questions on sensitive 

topics like sexual assault. As a result, two hypotheses were formed: 

1. That larger survey incentive amounts would result in a higher response rates, and 

2. Once controlling for differences in response, the victimization rates would not differ across the different 

survey incentive amount conditions. 

Methodology 

The CCSVS included nine U.S. institutions of higher learning. Data were collected via a web survey during the 

spring of 2015, with four of the nine institutions included in the incentive experiment. The $25 vs. $10 experiment 

was conducted at two schools and the $40 vs. $25 experiment was conducted at two schools. Because school context 

is likely to influence the impact of incentives, it is necessary to vary the conditions within each of the participating 

schools to rule out the possibility of school characteristics being responsible for any observed variability in the 

conditions. Therefore, rather than assigning all sampled students in a given school to receive one incentive amount 
and then comparing its impact to the impact of a different incentive amount used at another school, the experimental 

conditions were varied (i.e., students were randomized to receive one or the other incentive amount) within each 

participating school. The experiment aimed to determine the optimal dollar amount for increasing response rates 

while balancing the costs of survey administration, which led to the decision to test three amounts: $10, $25, and 

$40. These amounts are similar to those used successfully in other federally funded surveys of college students, 

such as the Beginning Postsecondary Students Longitudinal Study (Wine et al., 2011) and the National 

Postsecondary Student Aid Study (Wine et al., 2013). Students at two schools were randomized to receive either a 

$10 or $25 gift card, and students at two other schools were randomized to receive either a $25 or $40 gift card. At 

the five remaining schools, students were offered a $25 gift card as incentive for completing the survey.

1

 

Both experiments were powered to detect small differences in participation (3.65% or less) and victimization (2.64% 

or less) rates (Table 1). 

Table 1. Minimum detectable differences in survey participation and sexual assault rates for the 

incentive experiment 

Females Males 

Minimum Minimum 

Detectable Detectable 

N Difference N Difference 

Participation Rates 

$25 vs. $10 9,898 2.80 % 7,277 3.04 % 

$25 vs. $40 7,118 3.32 5,535 3.65 

Victimization Rates 

$25 vs. $10 4,395 2.41 2,176 1.71 

$25 vs. $40 3,623 2.64 2,030 1.79 

Source: Campus Climate Survey Validation Study (CCSVS), 2015 

Note: Detectable difference calculations assume a two-sided Pearson’s chi-squared test with alpha=0.05 and 80% 

power. Observed sample sizes, participation rates, and victimization rates were used in the calculations, and 

detectable differences shown are in the direction of the observed difference. 

Results of Bivariate Analysis 

The $25 incentive led to significantly higher survey participation rates than the $10 incentive for both males and 

females (Table 2). For both sexes, participation rates were more than 5 percentage points higher for students who 

were randomized to the $25 incentive than the $10 incentive condition. For females, victimization rates were 

significantly higher for students who received the $10 incentive (observed difference of 1.7 percentage points), 

whereas no significant differences were found for males. 

Table 2. Comparison of participation and sexual assault rates, by incentive amount ($25 vs $10), 

2014–2015 academic year 

Number 

$25a $10

Percent SE Number Percent SE

Participation 

Males 

 

1,186 

 

32.6 

 

% 

 

0.4 

 

% 

 

990

 

27.2 

 

%*

 

0.3 

 

% 

 

1

 Study contact materials informed sample members that if they completed the survey, they would be able to 

choose among nine online and in-store gift card options as a token of appreciation. The nine gift cards they 

could choose from were Amazon.com, Chili’s, CVS, Domino’s Pizza, Dunkin’ Donuts, Panera Bread, Staples, 

Starbucks, and Walmart. Gift cards were sent to respondents electronically within two business days of 

completing the survey. 
Number 

$25a $10

Percent SE Number Percent SE

Females 2,325 47.0 0.3 2,070 41.8 * 0.3 

Victimization 

Males 34 2.9 0.3 25 2.5 0.2 

Females 179 7.7 0.3 195 9.4 * 0.3 

Source: Campus Climate Survey Validation Study (CCSVS), 2015 

Note: SE = standard error. 

a

 Reference group. 

* Rate for $10 incentive is significantly different from rate for $25 incentive at the alpha=0.05 level. 

When evaluating the effects of the $40 incentive vs. the $25 incentive, there were no statistically significant 

differences in survey participation rates for males or females when pooling across the two schools (see Table 3). 

For females, sexual assault victimization prevalence rates were significantly higher for students who received the 

$40 incentive than for those who received the $25 incentive, whereas no significant differences were found for 

males. 

Table 3. Comparison of survey participation and sexual assault rates, by incentive amount ($25 vs 

$40), 2014–2015 academic year 

Number 

$25a $40

Percent SE Number Percent SE

Participation 

Males 991 36.0 % 0.7 % 1,039 37.3 % 0.7 % 

Females 1,769 50.3 0.6 1,854 51.5 0.6 

Victimization 

Males 30 3.0 0.4 27 2.6 0.3 

Females 133 7.5 0.4 163 8.8 * 0.5 

Source: Campus Climate Survey Validation Study (CCSVS), 2015 

Note: SE = standard error. 

a

 Reference group. 

* Rate for $40 incentive is significantly different from rate for $25 incentive at the alpha=0.05 level. 

Results of Model-Based Analysis 

It’s not clear if the difference in victimization rates by incentive amount was due to the monetary difference or to 

differences resulting in composition due to response rates. Initial random assignment will not be able to account for 

differences in response propensities. To address this concern, two logistic regression models were fit for each sex for 

each incentive experiment to determine if controlling for student characteristics altered the bivariate findings: a 

participation model and a victimization model. 

Participation Models 

In the participation models, the odds of participating in the survey were assessed for both incentive conditions. Due 

to differences in student characteristics provided by schools on their rosters, different control variables were used in 

each model. For the $25 vs. $10 experiment, odds ratios were adjusted based on each student’s age, year of study, 

full- or part-time status, race/ethnicity, and school attended. For the $25 vs. $40 experiment, odds ratios were 

adjusted based on each student’s age, year of study, and school attended. The school-by-incentive amount 

interaction was included in all models to allow for different results between the incentive experiment schools. 
Adjusted odds ratios of survey participation for the $25 vs. $10 and $25 vs. $40 experiments, respectively, by 

school2

 and sex were generated (Figure 1 and Figure 2). In both figures, the $25 incentive is the reference group 

and the odds of participating in the CCSVS Pilot Test for the $10 or $40 incentive group relative to the $25 

incentive group are shown. Thus, odds ratios of more than one (horizontal line) indicate that the alternative 

incentive amount ($10 or $40) resulted in a higher likelihood of survey participation, whereas odds ratios of less 

than one indicate that the $25 incentive resulted in a higher likelihood of survey participation. 

The overall (pooled) estimates for both males and females are well below the line, as the odds that students who 

received the $10 incentive would participate were about 0.8 times (odds ratio of 0.77 with a 95 percent CI of 0.74 to 

0.81 for males and 0.81 with a 95 percent CI of 0.78 to 0.84 for females) those who received the $25 incentive when 

controlling for student characteristics (Figure 1). For males, the odds ratios for School A and School B were not 

significantly different. For females, the odds ratios for School A and School B were significantly different, but the 

effects were relatively small and in the same direction (odds ratio of 0.86 with a 95 percent CI of 0.86 to 0.87 for 

females at School A and 0.76 with a 95 percent CI of 0.71 to 0.81 for females at School B). 

Figure 1. Adjusted odds ratio of survey participation for Incentive Experiment 1 ($25 vs. $10), by sex 

and school, 2014–2015 academic year 

Source: Campus Climate Survey Validation Study (CCSVS), 2015 

Note: $25 incentive is the reference group; no mapping between school numbers and school letters is implied. 

The overall (pooled) odds ratios for Incentive Experiment 2 ($25 vs. $40) are slightly more than one (odds ratios of 

1.06 for males and 1.05 for females), but the 95 percent confidence bands include one (95 percent CI of 0.98 to 1.15 

for males and 0.98 to 1.11 for females) (Figure 2). Thus, the odds of participation in the survey for the two 

incentive amounts are the same when controlling for student characteristics. However, when examining the odds 

ratios at the school level, it is evident that opposite trends were observed for females. At School A, significantly 

higher survey participation rates were observed for the $40 incentive group (odds ratio of 1.15 with 95 percent CI of 

 

2

 The two schools in each figure are denoted by School A and School B, but these represent different schools in 

each figure and no mapping to Schools 1-9 is implied for these four schools.
1.04 to 1.28), whereas at school B significantly higher participation rates were observed for the $25 incentive group 

(odds ratio of 0.92 with 95 percent CI of 0.87 to 0.98). Because the effects were in opposite directions, the pooled 

effects cancelled out, leading to no detectable differences in the impact of different incentive amounts on survey 

participation. 

Figure 2. Adjusted odds ratio of participation for Incentive Experiment 2 ($25 vs. $40), by sex and 

school, 2014–2015 academic year 

Source: Campus Climate Survey Validation Study (CCSVS), 2015 

Note: $25 incentive is the reference group; no mapping between school numbers and school letters is implied. 

Victimization Models 

For the victimization models, the odds of experiencing sexual assault for the different incentive amounts were 

assessed, controlling for characteristics of the students. For Experiment 1 ($25 vs. $10), the models controlled for 

each student’s year of study, race/ethnicity, gender identity, sexual orientation, age, full- or part-time status, and 

school attended. For Experiment 2 ($25 vs. $40), the models controlled for each student’s year of study, 

race/ethnicity, gender identity, sexual orientation, age, and school attended. The school-by-greeting interaction was 

also included to allow for different results between schools. As with the participation graphic, the $25 incentive is 

the reference group and the odds of identifying as experiencing sexual assault for the alternative incentives ($10 or 

$40) relative to the $25 incentive are shown. Odds ratios of more than one indicate that more students indicated that 

they experienced sexual assault in the alternative incentive group, whereas odds ratios of less than one indicate that 

more students identified as experiencing sexual assault with the $25 incentive group. 

For males, the adjusted odds ratio overall and for both schools in Incentive Experiment 1 are very close to one, and 

the 95 percent confidence intervals include one. The odds ratios were 0.93 (95 percent CI of 0.57 to 1.50), 1.33 (95 

percent CI of 0.69 to 2.55), and 0.66 (95 percent CI of 0.33 to 1.33) for overall, School A, and School B, 

respectively (see Figure 3). This indicates no significant difference in sexual assault victimization rates between the 

$25 and $10 conditions when controlling for student characteristics. However, for females the overall and schoollevel estimates are more than one, indicating that students in the $10 incentive group were more likely to identify as 
experiencing sexual assault than students in the $25 incentive group. The odds ratios were 1.26 (95 percent CI of 

1.05 to 1.50), 1.20 (95 percent CI of 0.91 to 1.57), and 1.31 (95 percent CI of 1.05 to 1.65) for overall, School A, 

and School B, respectively. 

Figure 3. Adjusted odds ratio of sexual assault rates for Incentive Experiment 1 ($25 vs. $10), by sex 

and school, 2014–2015 academic year 

Source: Campus Climate Survey Validation Study (CCSVS), 2015 

Note: $25 incentive is the reference group; no mapping between school numbers and school letters is implied. 

For the second incentive experiment ($25 vs. $40), there are no detectable differences in the sexual assault 

victimization rates for males when controlling for characteristics of the students (see Figure 4). The odds ratios 

were 0.87 (95 percent CI of 0.53 to 1.43), 0.76 (95 percent CI of 0.35 to 1.66), and 1.00 (95 percent CI of 0.54 to 

1.84) for overall, School A, and School B, respectively. For females, after controlling for student characteristics, the 

overall effect is no longer significant (odds ratio of 1.15 with 95 percent CI of 0.94 to 1.41), but it is still significant 

for one of the schools. For School A, sexual assault victimization rates are higher in the $40 group than the $25 

group (odds ratio of 1.47 with a 95 percent CI of 1.08 to 2.00). 
Figure 4. Adjusted odds ratio of sexual assault rates for Incentive Experiment 2 ($25 vs. $40), by sex 

and school, 2014–2015 academic year 

Source: Campus Climate Survey Validation Study (CCSVS), 2015 

Note: $25 incentive is the reference group; no mapping between school numbers and school letters is implied. 

Discussion 

Overall, the incentive experiments showed that survey participation rates are significantly higher for both males and 

females when a $25 incentive is offered rather than a $10 incentive. When comparing a $25 and a $40 incentive, the 

results are less clear. For males, no significant differences were found in survey participation rates. However, for 

females, participation rates were significantly different, but the direction of the effect differed between the two 

schools in the experiment.

Not only does the incentive amount affect the rate of survey participation, but it also appears to affect the 

composition of the sample regarding the key survey outcome (sexual assault victimization prevalence). For females, 

the $10 incentive group had a higher prevalence of sexual assault than the $25 group, even when controlling for 

student characteristics in a modeling context. This provides some evidence that sexual assault victims may have 

been more likely to participate in the CCSVS Pilot Test even when a lower incentive amount was offered, and that 

the higher incentive amount brought in more non-victims. Again, the results of the $25 vs. $40 experiment were 

less clear. Although the overall difference in sexual assault victimization prevalence rates for females was no longer 

significant when controlling for student characteristics in a modeling context, there was a significant difference at 

one school, with students who received the $40 incentive having a significantly higher rate of sexual assault 

victimization than students who received the $25 incentive. It is unclear why the higher incentive amount, at least in 

some schools, would lead to lower survey participation, or be more likely to attract sampled members who were 

victims of sexual assault. 

The selection of the appropriate incentive amount for future studies similar in scope must consider the impact on 

both survey participation rates and sexual assault victimization rates. It is clear that the $25 incentive provides 

survey participation gains over the $10 incentive, and likely results in a significantly larger and more representative 
sample. It is less clear, however, whether moving to a $40 incentive offers any advantage. Thus, it is recommended 

that incentives be in the $20 to $30 range for future studies of this kind. 

Disclaimer: This document was prepared using Federal funds provided by the U.S. Department of Justice under 

Cooperative Agreement number 2011-NV-CX-K068. Any opinions and conclusions expressed herein are those of the 

author(s) and do not necessarily represent the views of the Bureau of Justice Statistics and the U.S. Department of 

Justice.

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of Justice. http://www.bjs.gov/content/pub/pdf/ccsvsftr.pdf 

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(NPSAS: 12): Data file documentation. http://nces.ed.gov/pubs2014/2014182.pdf 

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Longitudinal Study (BPS: 04/09): Full-Scale Methodology Report. 

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