Survey incentives: what works and what it costs

Cash in advance, vouchers or a prize draw: which survey incentives increase participation, what an additional response costs and how to test it yourself.

An incentive is something you give people in return for taking part in a survey. In surveys of the general population, the research shows that a small, guaranteed amount of money that every invitee receives in advance works best. A reward promised for completing the survey works less well, and prize draws and donations usually work even less well (Malhotra and Birks 2007, p. 446; Jacob et al. 2019, p. 234; Schnell 2019, p. 173). Whether an incentive pays off for your survey comes down to two questions: what does each additional usable questionnaire cost, and who does the incentive bring in?

I'll answer five questions, one after the other:

• What types of incentives are there, and what does research say about how well they work?
• How much should an incentive be?
• What does an additional usable response cost, and when is money in advance worth it?
• How do you test an incentive yourself, and who does it encourage to respond?
• What applies to prize draws and to employees, customers and students?

I get this question from students before the fieldwork for their thesis as well as from teams that survey customers or employees: "Does a prize draw help, or am I throwing money away?" My practical advice up front: with people who have a connection to the topic, I'd first emphasize the purpose of the survey and the promise to share the results. With strangers, the research cited here tends to favor a small, guaranteed reward. How to calculate your response rate and increase it with invitations and reminders is covered in Survey response rate. This article is only about incentives for survey participation, but it covers them thoroughly.

What types of survey incentives are there?

Incentives are small gifts, less often services, and above all money (Schnell 2019, p. 172). In Germany, they were largely unusual outside mail surveys until around 2000, and that has changed quickly since then (Schnell 2019, pp. 172-173). The most important distinction is timing: does the person receive the incentive before the survey, without conditions, or only after completing it?

The lines between these types are blurred. Compensation for time is usually a promised incentive with a different rationale: it pays for people's time instead of persuading them to take part. A voucher can come with the invitation or be sent only after completion. What matters most for the effect is whether the incentive is guaranteed and when it arrives.

Why does an incentive work at all? Möhring and Schlütz explain participation partly through the principle of reciprocity: someone who is asked politely and perhaps receives a small gift wants to return the favor (Möhring and Schlütz 2019, p. 44). People who have already received something feel the strongest obligation, as studies of mail surveys show (Diekmann and Jann 2001, cited in Möhring and Schlütz 2019, p. 139). That's why an incentive in advance usually works better than one people have to earn first.

Do survey incentives work? What the research says

Research on incentives comes to mixed conclusions. A few findings are stable, though: money is more effective than gifts, incentives handed out in advance are the most promising, and the value has to be appropriate so that people don't feel they're being paid (Möhring and Schlütz 2019, p. 47). Schnell sums up the state of research with the title of a paper: "Charities, No; Lotteries, No; Cash, Yes" (Warriner et al. 1996, cited in Schnell 2019, p. 173). In the general population, guaranteed cash incentives paid before the survey almost always work better than other types, in every survey mode (Schnell 2019, p. 173). Let's look at the types one by one, from the strongest to the weakest.

Prepaid incentives: the strongest type

Malhotra and Birks put it plainly: "Prepaid incentives have been shown to increase response rates to a greater extent than promised incentives" (Malhotra and Birks 2007, p. 446). A German textbook adds that, if you have a budget for incentives, the best way to increase response is to give every invitee the incentive before the survey, whether they take part or not (Jacob et al. 2019, p. 234). That sounds wasteful, because some of the money goes to people who never respond. One explanation is reciprocity: people may see the incentive as a gesture of trust rather than payment for their work.

Providing cash in advance is harder in an online survey than in a mail survey, where you can enclose a coin or a bill. A voucher code in the invitation is the obvious solution, but it isn't the same as cash. An experiment with 1,750 randomly selected students compared, in a web survey, a mailed prenotification letter with prepaid cash, with a prepaid voucher and with a voucher after completion. The prenotification letter with prepaid cash produced the most responses and the highest share of people who, once they had started, answered to the end. The prepaid voucher didn't achieve that (van Veen et al. 2016, abstract). The fewest missing answers to individual questions, on the other hand, came with the prenotification letter and a voucher after completion (ibid.). So no type wins on every count. What that means for costs is covered below in the section Cost.

Promised incentives: cheaper, but weaker

A promised incentive goes only to those who complete the survey (Malhotra and Birks 2007, p. 446). It works less well than an incentive in advance (Jacob et al. 2019, p. 234). On the other hand, you only pay those who complete the survey, so you don't have to pay every invitee up front. For many surveys with a small budget, for example in a thesis, this is the realistic option.

Prize draw: popular, but disputed

In the online surveys I see, the prize draw is probably the most common type, because it costs little: three vouchers are cheaper than one voucher for everyone. According to the research cited, however, it's weaker than a guaranteed incentive. Jacob et al. expect a weaker effect when a larger prize is raffled off (Jacob et al. 2019, p. 234), and Schnell advises against lotteries altogether (Schnell 2019, p. 173).

The picture isn't entirely clear. Malhotra and Birks report on a telephone survey by a New Zealand market research agency that tested four elements of the introduction: a prize draw for a weekend holiday, the assurance that it wasn't a sales call, the assurance of confidentiality, and a shorter or longer description of the topic. In their words: "Overall, only the incentive significantly increased the response rate." It worked best together with the assurance that nothing would be sold (Malhotra and Birks 2007, p. 446). So a prize draw can work. According to the sources cited, though, it usually increases participation less than a guaranteed incentive in advance. Which option is cheaper for your budget is something you need to calculate separately.

Donation: well meant, weak in effect

A donation for every completed questionnaire feels good and avoids the impression that you're buying responses. Based on the research, however, you should refrain from it (Schnell 2019, p. 173). If a donation fits your organization, don't expect a big effect on response.

Results and purpose: non-monetary incentives

An existing results report can be shared with little extra effort and shows participants what has become of their answers. You offer it at the end of the questionnaire, either with a form for contact details or with a note about a web page where the results will be published at a certain time (Möhring and Schlütz 2019, p. 116). In customer surveys, the promise to share the results makes the survey more credible (Weinreich and von Lindern 2008, p. 81).

What is known about online surveys

In online surveys, material incentives are used to encourage participation. A meta-analysis by Göritz of 32 experiments with a total of 212,810 people found that material incentives increase the odds of starting a web survey, with an odds ratio of 1.19 (95% confidence interval 1.13 to 1.25). Across 26 experiments with 7,073 people, they also increased the odds of completing a survey once started, with an odds ratio of 1.27 (Göritz 2006, abstract).

What does an odds ratio of 1.19 mean in percent? That depends on the baseline. If 25% of invitees start without an incentive, the conversion looks like this:

With a fixed baseline of 25% without an incentive, the limits of the confidence interval correspond to 27.4% to 29.4% with an incentive (my own conversion). So on average, an incentive helps, but it's no miracle cure. If someone promises that a prize draw will double your response rate, be skeptical.

How I see it

Slide 114 of my course says: "Provide incentives. Preferably non-monetary incentives." (Marx 2026, slide 114). That only seems to contradict the research. The findings on money in advance come mainly from surveys of the general population (Schnell 2019, p. 173), that is, from people who owe you nothing. With customers, members or employees, it's different. A customer survey raises expectations, usually that something will improve, and promising to share the results makes the survey more credible (Weinreich and von Lindern 2008, p. 81). So with people who have their own reason to take part, I'd first emphasize the purpose and the feedback. That's how I read the sources together. Strangers without a connection lack that reason, and there a small, guaranteed reward is more likely to help. And an incentive doesn't replace a good questionnaire: even a cash incentive for complete participation doesn't prevent respondents who are forced to answer every question from breaking off earlier and more often (Décieux et al. 2015, cited in Jacob et al. 2019, p. 123).

How much should a survey incentive be?

There's no universally valid amount, and I won't give you one. The literature does offer some guidance, though. For larger studies with extra effort, such as panels or diaries, and for hard-to-reach groups, about 10 euros was considered usual in 2019, as much as one hour of a student assistant's work (Schnell 2019, p. 173). The effect seems to grow with the amount and to be stronger the more burdensome the survey appears (ibid.). Malhotra and Birks also see a positive relationship between amount and response, but warn that "the cost of large monetary incentives may outweigh the value and quality of additional information obtained" (Malhotra and Birks 2007, p. 446).

Three rules help with the decision:

1. Appropriate rather than high. The value has to be appropriate, otherwise people feel they're being paid and push back (Möhring and Schlütz 2019, p. 47). Unusually high amounts can cause suspicion (Schnell 2019, p. 173). Base the amount on the time you ask for, not on the response you'd like to get.
2. One payment rather than several small ones. In a preregistered experiment in the 2022 Survey of Consumer Finances, a single prepaid incentive of 15 dollars increased response compared with 5 dollars, with similar data quality. The same 15 dollars split into two payments of different sizes didn't increase response, but made the fieldwork take longer and increased the interviewers' workload (Chang et al. 2024, abstract). This is a US household survey, so the amounts aren't directly applicable to other settings. The finding still offers useful guidance.
3. The same for everyone. Everyone who might be in contact with each other should receive the incentive in the same way and at the same time. If people find out about unequal rewards, reactance and high dropout are likely (Schnell 2019, p. 173). And the value of an incentive must never depend on how someone answers. That violates the principle of justice in research ethics (Möhring and Schlütz 2019, p. 3).

Survey incentive cost: what does an additional usable response cost?

Most people only calculate the budget for vouchers. Another number is more useful: what does each questionnaire cost that you wouldn't have received without the incentive and that passes your quality check? Let's work through an example. The numbers are invented, and the same ones appear in the article Survey response rate.

A university team surveys students at two campuses, with 400 eligible students at each. A coin toss decides which campus gets the incentive. Students at different campuses have little contact with each other. Why that matters is explained in the section Experiment. Both groups receive the same invitation, the same questionnaire and the same reminders. One group also receives a guaranteed voucher worth 5 euros for every completed questionnaire. A guaranteed voucher only costs money for those who complete. Money in advance works better, but costs money for every invitee, more on that below.

My own calculation with invented data.

In the example, the group with the incentive delivers 10 percentage points more completions, 40 additional completions and 35 additional usable cases, at 700 euros in additional costs. The vouchers go to all 140 who complete, including the 10 whose questionnaires are later excluded in the check. That's 50 euros for questionnaires you don't use. By the way, these 50 euros aren't a mistake. They're the price of keeping your promise. So each additional usable case costs:

This marginal cost is the really interesting number, not the average of 10.00 euros per case. The average includes the cheap cases you would have received without the incentive anyway. The question is: is each of the estimated 35 additional usable cases worth 20.00 euros to you?

The answer depends on your goal. If you need 120 usable questionnaires for your analysis, the incentive in this example is the difference between a dataset that's too small and one that's large enough. How many you need is covered in the article Calculating sample size. If you could simply have invited more people instead, that would usually have been the cheaper route: additional online invitations cost little more than the time it takes to send them. An incentive pays off mainly when the number of people you can invite is limited.

And if you pay in advance?

Suppose you give all 400 invitees in the second group a voucher code worth 5 euros with the invitation. Then the vouchers cost 400 · 5 = 2,000 euros, no matter how many respond, and the group costs 2,600 euros in total. How much this increases response in your target group, I don't know, and I won't invent a number for it. What you can calculate, though, is when it pays off. If an additional usable case shouldn't cost more than the 20.00 euros with the guaranteed voucher, the prepaid group needs at least 2,000 / 20.00 = 100 additional usable cases, that is, 195 of 400, or 48.8%. With a similar exclusion rate in the quality check as above, that would correspond to about 210 completions, or 52.5% (my own calculation).

Whether that's realistic depends on your group. But the calculation shows why money in advance works best in research (Schnell 2019, p. 173) and still isn't always the cheapest way to an additional case. Van Veen et al. also found the highest total costs with prepaid cash, but per respondent, the group without a prenotification letter and without an incentive was the most expensive (van Veen et al. 2016, abstract). The abstract doesn't say what an additional case cost. That's exactly the number you should calculate for your survey.

What no voucher calculation shows

Your time is part of the cost. Vouchers have to be bought, codes sent, winners notified and questions answered. The effort involved in incentives shouldn't be underestimated (Schnell 2019, p. 173). At universities and in publicly funded research in Germany, paying out incentives involves considerable administrative effort and usually needs a special justification in the funding application, which is why incentives are often left out even where they would make sense (Schnell 2019, p. 173, n. 34). Before you start, clarify who pays, how it's accounted for and by when everyone will receive their incentive.

Testing incentives in a small experiment

You'll only know whether an incentive pays off for your target group once you've tested it. The research offers general guidance, but it can't guarantee results for your survey. For panel studies, Schnell recommends clarifying through your own preliminary studies, if necessary, whether incentives change the respondents or the way they answer (Schnell 2019, p. 343). The same logic applies to the effect on participation in a single survey. An experiment with two groups is the cleanest tool for this.

1. Define a question. Write down beforehand what you want to know, for example: "How does a guaranteed voucher worth 5 euros change the share of completed questionnaires and the cost per usable case?" Not: "Do incentives work?"

2. Assign at random. Split the people on the same invitation list into groups at random, for example with a random number in Excel. Not by degree program, department or alphabet. Assignment to groups should be impartial, for example random (Möhring and Schlütz 2019, p. 3). If the people have a lot of contact with each other, assign whole groups with little contact instead, such as campuses, as in the example above. Keep a record of the assignment for those who don't respond, too, or you won't know your denominator later.

3. Change only one thing. The invitation, sender, subject line, questionnaire, reminders and field period stay the same. If you change the subject line and the incentive at the same time, you won't know at the end what made the difference.

4. Set criteria in advance. What counts as completed, what as usable? Set quality rules before you see the data, and apply them the same way in both groups. A fully completed questionnaire isn't automatically a good case.

5. Analyze and report. Compare response, usable cases, costs and the composition of both groups. Report the numerator and denominator, not just percentages.

How well can chance explain the difference?

In the example above, 25% complete the survey without an incentive, compared with 35% with an incentive. A two-sided z-test for two independent proportions gives z = 3.09 and p = 0.002. If both groups had the same probability of completing, a difference at least this large in either direction would be expected in only about 2 out of 1,000 such trials. With 100 people per group and the same proportions, z would be 1.54 and p 0.12. This smaller study wouldn't show a statistically significant difference (my own calculation). Strictly speaking, the test assumes that individual people were randomly assigned. With two whole campuses, the difference also includes everything else that distinguishes the campuses. The calculation then shows the order of magnitude, not clean proof.

So plan the group size beforehand. With random assignment of individuals, you need about 329 people per group to detect a difference of 25% versus 35%, at a two-sided significance level of 5% and 80% power. The following sample sizes also assume independent observations and don't apply directly to a comparison of two whole campuses. To be honest, our invented example is optimistic: 25% versus 35% corresponds to an odds ratio of 1.62. In Göritz's meta-analysis, incentives increased the odds of starting a web survey by a factor of 1.19 and the odds of completing it, among those who had started, by a factor of 1.27 (Göritz 2006, abstract). To illustrate the scale of the effect, applying both odds ratios together in three hypothetical baseline scenarios gives an overall completion proportion of about 29% to 30%, up from 25%. This model calculation assumes that both effects apply together and is not a finding of the meta-analysis. For these scenarios, at a two-sided significance level of 5% and 80% power, you would need roughly 1,100 to 1,800 people per group (my own calculation). A small effect simply can't be detected in a small survey. In that case, the honest conclusion is "the evidence is inconclusive", not "the incentive doesn't work".

Measure more than the response rate

An incentive can change things at several points. This planning aid is my own compilation, not a validated instrument:

An experiment that stays fair

An experiment with incentives has a tricky side: one group gets something, the other doesn't. As described above in the section on the amount, this risks reactance (Schnell 2019, p. 173). In a degree program or department where everyone talks to each other, that's a real risk. That's why the example above takes place at two campuses: groups at different campuses have little contact with each other. If possible, test the incentive this way, with groups that hardly interact. For fairness, you can give the control group the same incentive as a thank-you after the fieldwork ends. In the example, that costs an extra 100 · 5 = 500 euros. If you plan for this payment, the additional costs of the whole experiment compared with no incentives rise to 1,200 euros, which, with the estimated 35 additional usable cases, comes to 34.29 euros per additional case. The 20.00 euros above apply to the version without this thank-you afterward (my own calculation). This only helps against reactance as long as the control group doesn't learn about the voucher during the fieldwork. If the groups talk to each other, the measurement is biased. Discuss with your supervisor or ethics committee whether the information you give participants about this arrangement is sufficiently transparent.

Bias: who does the incentive bring in?

An incentive changes not only how many people respond, but possibly also who responds and how. More responses don't automatically mean less bias. The article Representative sample explains when a sample can still provide useful information. Nonresponse bias arises when respondents and nonrespondents differ systematically in the characteristic you're studying. The article Survey response rate explains this in detail.

The composition can shift. The evidence is mixed on whether incentives change the composition of the sample (Göritz 2007, cited in Möhring and Schlütz 2019, p. 145, n. 63). In a web survey of students, prepaid cash did increase response, but compared with administrative records it may have produced less representative data (Parsons and Manierre 2014, abstract). In access panels, people who are less well off financially are more likely to be motivated by incentives to keep taking part (Göritz 2008, cited in Schnell 2019, p. 292). That can close a gap or open a new one, depending on who was missing before.

The incentive itself can influence who responds. A material prize mainly appeals to people who want it. In group discussions with guests of the German Youth Hostel Association, an overnight-stay voucher was offered as compensation for time. The authors suspect that it mainly attracts people who want to stay at a youth hostel again anyway (Bäßler et al. 2009, p. 57). In a customer satisfaction survey, this could mean that the views of disappointed customers in particular get too little weight. That's why I'd choose a neutral incentive, for example a voucher that everyone can use equally well, rather than a product from your own company.

Answers can become friendlier. Weinreich and von Lindern consider rewards in customer surveys controversial. Those who respond may mainly be people who want to win a weekend on the North Sea, and some may give more favorable answers (Weinreich and von Lindern 2008, p. 81). Negative effects on data quality are disputed overall (Möhring and Schlütz 2019, p. 47).

Multiple participation becomes attractive. If every questionnaire earns a voucher or a ticket in a draw, people have a reason to take part more than once. Weinreich and von Lindern name exactly this as one of the two main causes of multiple participation, alongside the intention to skew the results. The risk is greatest with open surveys on the internet, and closed surveys with unique access credentials are safer (Weinreich and von Lindern 2008, p. 175). Möhring and Schlütz also warn of multiple participation in surveys without an access code (2019, p. 146).

Open calls attract incentive hunters. Self-recruited online panels also include "incentive hunters" (Jacob et al. 2019, p. 92). If you share a link with a prize draw openly on social networks, people who aren't part of your target group at all may respond.

What you can do about it: wherever possible, invite a known list personally. Prevent multiple participation technically. Ask a question at the start that checks whether someone belongs to the target group. At the end, compare respondents with known characteristics of the target group, separately for each group in an experiment.

Survey prize draws: data protection and organization

If you decide on a prize draw, you need the winners' contact details, but not next to their answers. Möhring and Schlütz recommend forwarding participants to a different questionnaire at the end, so that the email address isn't linked to the answers (Möhring and Schlütz 2019, p. 116). That way, the actual survey stays anonymous. Say so in the invitation, for example like this:

Agree on the text in advance with your data protection officer or the responsible office in your organization. Clarify three points:

• Consent separate from marketing. For the prize draw, you may ask for consent to process the email address, but that consent must not be tied to the address also being used for advertising. This is explained in the article Data protection in online surveys, where you'll also find an example of terms of participation for a prize draw.
• Terms of participation. Who can win, by when, how is the draw carried out and how are winners notified, and what happens if someone doesn't get in touch?
• Other rules. Whether other legal or tax rules apply to your prize draw, for example with high-value prizes, with prize draws run by a company or with funds from a research project, is best clarified with the same office.

Special cases: employees, customers and students

Employee survey

For employee surveys, the literature is cautious. Incentives that are too expensive could be seen as payment or bribery (Borg 2003, cited in Wiertalla 2013, p. 184). Higher participation can even lower quality if less motivated employees only take part because of the reward (Bösch 2011, cited in Wiertalla 2013, p. 184). Trost et al. advise against incentives altogether: an employee survey is not a "prize draw" (Trost et al. 1999, cited in Wiertalla 2013, p. 184).

A case from practice shows the limits. At Ingram Micro, where Wiertalla studied the employee survey, a prize draw had accompanied the survey for years, with products from the company's own range sponsored by manufacturers. Whether it increased participation was hard to judge. Only about half of those eligible took part in the prize draw, while participation in the survey itself was over 70%. One employee complained that the prize draw was only meant to increase participation (Wiertalla 2013, p. 184).

What works instead is purpose. Linke describes companies that make an event of participation and follow-up, for example by giving teams breakfast vouchers so they can discuss the results over breakfast (Linke 2018, p. 67). That's an incentive for the team, not for the individual questionnaire, and it leads directly to working with the results. More on this in the article Employee survey.

Students and theses

Students often survey other students, on a small budget. Depending on the university, options include course credit, feedback on the results or a prize draw (Möhring and Schlütz 2019, pp. 114 and 116). The 700 euros from the example above are rarely affordable for a bachelor's thesis. So it's better to rely on a larger invitation list than on an expensive incentive. How to find respondents is covered in Where do I find respondents for my survey, and how the survey fits into your thesis in the article How to write my thesis.

Organizing incentives with QUESTIONSTAR

Here's how our own product can help. QUESTIONSTAR doesn't pay out incentives. You organize vouchers and prize draws yourself. It also doesn't increase your response rate by itself. But it helps you manage a survey with incentives and assess their effect.

Preventing multiple participation. In the Access settings, you can make sure the same person can't take part more than once. If you offer incentives, you should always switch this on.

Inviting personally and reminding selectively. You can invite people by email with personal links and send reminders only to those who haven't responded yet. This also works for anonymous surveys, at both anonymity levels explained in the article Employee survey. For an incentive experiment, create two copies of the same questionnaire, each with its own contact list. That keeps the groups separate: the completions widget and the export show each group on its own, even in anonymous surveys, and you know your denominator.

Tracking progress. The completions widget in the dashboard shows how many people have started and how many have completed the survey. The percentage there is completed out of started, that is, the completion rate. You calculate the response rate per group yourself, with the number of people invited to each copy in the denominator.

Exporting and comparing. You export the responses for each copy as an Excel, CSV or SPSS file and compare response, missing answers and the composition of both groups there.

Checklist: planning an incentive

Frequently asked questions about survey incentives

What is a survey incentive?

An incentive is something given in return for taking part in a survey, for example money, a voucher, a ticket in a prize draw, a donation or a results report. An important distinction is whether the incentive is given in advance without conditions or only after completion (Malhotra and Birks 2007, p. 446).

Which survey incentives work best?

In surveys of the general population, the research shows that a small, guaranteed amount of money in advance works best. Promised incentives after completion and prize draws work less well, and Schnell advises against donations and lotteries (Jacob et al. 2019, p. 234; Schnell 2019, p. 173). With people who have a connection to the topic, I'd first emphasize the purpose and the promise to share the results.

Is a prize draw worth it for a survey?

It costs little and can increase response (Malhotra and Birks 2007, p. 446), but it usually works less well than a guaranteed incentive (Jacob et al. 2019, p. 234). For data protection, collect the contact details in a separate form, not next to the answers (Möhring and Schlütz 2019, p. 116), and prevent multiple participation.

How much should a survey incentive be?

Appropriate to the time you ask for. For demanding studies and hard-to-reach groups, about 10 euros was considered usual in 2019 (Schnell 2019, p. 173). Very high amounts can cause suspicion (Schnell 2019, p. 173), and the value must never depend on the answers (Möhring and Schlütz 2019, p. 3).

Do incentives bias survey results?

That's disputed (Möhring and Schlütz 2019, p. 47). An incentive can change who responds and, with customers, possibly how favorably they answer (Weinreich and von Lindern 2008, p. 81). So compare respondents with known characteristics of the target group.

Should you offer incentives in an employee survey?

The literature is cautious: incentives that are too expensive can be seen as bribery, and an employee survey is not a "prize draw" (Borg 2003; Trost et al. 1999, both cited in Wiertalla 2013, p. 184). So I'd prioritize visible improvements and action based on the survey results.

Sources

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I hope you find an incentive that suits your group, and that you have the patience to test it before you spend the whole budget.

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Dr. Paul Marx

Author: Dr. Paul Marx
Dr. Paul Marx is the founder and Managing Director of QUESTIONSTAR and was a professor of marketing at the University of Siegen.