In research ethics guidelines regarding payment for participation in research, it is considered acceptable to pay subjects in order to compensate them for direct expenses, their time and loss of income (see for example Council of Europe 1997 and 2010, CIOMS 2002 and NIH 2009). Views have differed on how to calculate compensation for use of (working) hours (see Dickert and Grady 1999, Saunders and Sugar 1999, Anderson and Weijer 2002, Draper et al. 2009, Stones and McMillan 2010). However, payment for participation beyond this form of compensation evokes the greatest disagreement. It is this more controversial form of payment that will be discussed here.

The first edition of this article was written at the same time as a guide regarding payment to participants in medical and health research (NEM 2009). Many of the points in this article can be found in an expanded edition of this guide.

Payment may be necessary to recruit subjects

The need to recruit subjects has been the main argument in favour of greater use of payment for participation in research. The number of research projects is increasing, and participants may soon become scarce. However, the question is whether the ability to pay should determine which projects would be the easiest to carry out.

For studies where a large and representative group of subjects is required for the project to have scientific value, payment or compensation may be critical in order to secure adequate recruitment. It is well documented that payment motives participation (see for example Stunkel and Grady 2011), particularly in projects that usually have difficulty recruiting participants, such as postal surveys (Singer and Bossarte 2006, Bentley and Thacker 2004, James and Bolstein 1990). In social science research, payment as an incentive has worked best for groups with low social and financial capital who have generally been difficult to recruit (Singer and Bossarte 2006, Groves et al. 2000, Simmons and Wilmot 2004).

However, financial gain is only one of several possible and real motivating factors among research subjects (see Stunkel and Grady 2011). Many research projects can (and must) therefore be carried out without offering pay. By focusing on other factors that can affect people's attitudes towards research (e.g. possible health benefits, interest in the purpose of the study, trust in the researcher/research, satisfaction of intellectual curiosity or a need to help others, sharing important experiences or participating in activities where they interact and talk with others), recruitment can also be increased in other ways than by offering payment (Dunn and Gordon 2005, Singer and Bossarte 2006).

Even though payment is not necessary in order to guarantee recruitment, it can still be a legitimate way of motivating people to participate in research. Some people both support the purpose of a project and consider the consequences of participation acceptable, but are uncertain about whether participation is worth the effort or the disadvantages. Thus, it is not necessarily problematic that a key factor in a person's decision to participate is an offer of payment (see Draper et al. 2009). It is critical that participation does not conflict with the person's interests. That, on the other hand, is not easy to determine.

Payment may consist of fair compensation, a reward or clarification of the request

Payment for participation in research can be seen as justified, regardless of any recruitment issues. It could be argued that people who participate in research that benefits society, effectively on behalf of us all, should receive some form of financial 'nuisance bonus' to compensate for the different forms of discomfort, burden and inconvenience associated with participation in research.
Research ethics guidelines in medicine and health allow the offering of payment as compensation for the burdens and disadvantages of participation in research. (See Council of Europe 1997 and 2010, CIOMS 2002, NIH 2009. See also the articles about the Convention on Human Rights and Biomedicine – the Oviedo Convention and CIOMS).

Another argument for offering payment or compensation to research subjects is that this is a way of showing appreciation for their contribution. Recognition of participants can be important to the researcher, the participant and their relationship. Researchers who interview people whose lives are financially and materially disadvantaged, may consider it a moral imperative to reciprocate (Lammers 2007). In many cultures and situations, however, there are better ways of doing this than by offering money.

Offering payment for participation in research can make it clear that participation is not requested as a favour. It is particularly important to highlight this when the researcher plays a dual role towards those who want to be included in a study. In medical research, payment can be a way of clearly showing that the participant is not being offered treatment, which in turn may counteract the so-called 'therapeutic misunderstanding', i.e. the erroneous idea held by many participants that they are participating in a project that can benefit their health, despite information to the contrary (Dickert and Grady 1999, NIH 2009).

Payment can be a threat to the interests of research subjects

It is a basic norm of research ethics that consideration of the participants' welfare and integrity takes precedence over the interests of science and society (see for example Article 3 of the Additional Protocol to the Convention on Human Rights and Biomedicine, concerning Biomedical Research and section 5 of the Health Research Act). (See also the article about the Health Research Act.) The question is whether the money that is offered to research subjects poses a threat to both the integrity and welfare of people.

One of the main arguments against offering money for participation in research has been that payment can serve as 'undue influence' during the information process or result in an 'obligation to deliver'. This can undermine the voluntary nature of the participation, both in relation to the actual consent to participate in the study and the opportunity to withdraw from it at any time. Money can induce a person to consent to participation or remain in the study, despite the purpose of the project or its procedures being at odds with their basic values and interests. There is reason to believe that a participant who is solely motivated by money, not the purpose of the project, may find it difficult to deal with any unforeseen adverse effects or burdens associated with a study.

It is particularly difficult to protect the research subjects' interests when people with diminished capacity to understand are included in research in return for payment. It can be much easier to understand that it is possible to achieve financial gain through participation than to understand the possible risks and burdens of a study. However, the problem here is not the payment in itself, but how one can be reasonably certain that the participant has actually understood the implications of the participation.

It has been claimed that an attractive sum of money can lead other potential participants to also pay less attention to the information about potential risks and discomforts than they should, which can result in unwanted surprises during participation. However, several studies indicate that these fears are unfounded (Cryder et al. 2010, Stunkel and Grady 2011). On the contrary, the study by Cryder et al. shows that potential participants studied the information about possible side effects and risks in greater detail when a large sum of money was offered, because they considered a high sum of money to be a sign of increased risks attached with the study.

On the other hand, this may mean that potential participants consider little or no pay for participation in a study to be a sign that the study is risk-free, which may not necessarily be the case (see Czarny et al. 2010). The fact that many people appear to link the size of the payment to the level of risk is therefore a challenge for the information and consent process.

If the sum is tempting enough, this may make people willing to assume risk and burdens that they would find unacceptable if no money were offered. An important point in this context has been that large sums of money, combined with risky or highly-burdensome participation in research, could lead to the exploitation of financially disadvantaged persons. There is therefore broad agreement in the research ethics community that the risks must always be minimised, and that high risk or a project causing great burdens can never be justified by paying the participants well (Resnik 2007, Council of Europe 1997, NIH 2009). The risk and the burden associated with a project must be acceptable in terms of the utility value, and the participants' welfare and integrity must be protected, regardless of the financial incentives offered.

Payment can have unfortunate consequences for the research in itself

One concern associated with payment to research participants is that participants may conceal important information in order to qualify for projects that offer payment, which makes the data less reliable (Bentlay and Thacker 2004). Researchers also fear that payment for interview studies that include people who are financially disadvantaged may lead informants to fabricate or at least adapt the information they provide, so that it matches the type of information they know that the researcher is looking for.

In studies where there is a close relationship between the researcher and the subject, another objection to payment is that this may interfere with the relationship between the two parties. In some situations, and when dealing with certain informants, offering payment will awaken their suspicions or be considered an insult. For certain research projects, it can therefore be important to consider whether offering payment (also lack of payment) may undermine key aspects of the relationship between the researcher and research subject, such as trust, a sense of equality and mutual respect.

The question has also been raised as to whether society has anything to gain from a greater degree of 'commercialisation' in the relationship between the researcher and research subject. The concern is that the researcher's personal sense of responsibility and relational obligation towards the participant can be weakened if this relationship is transformed into a business relationship, where the participant is considered more of a 'product' than a 'gift'.

A major objection against more extensive use of payment of research participants is that finances will determine which projects can be carried out. If payment is expected, and offering money is critical to the recruitment of participants, many projects with great potential to develop important, useful knowledge will need to be shelved due to financial constraints.

Can the negative consequences of payment be prevented or reduced?

The answer is probably yes, but there would be many ways to achieve this.

Some of the objections to payment of research subjects may be lessened if the payment is kept at a low level, and the amounts are standardized in terms of the project and efforts in question. At the same time, we know that what is little money for some people is a substantial amount for others, and the amount must therefore always be seen in the context of who the project wants to recruit.

The threat to the integrity and welfare of the participants may be averted to a large extent by improving the information and consent process, where focus is also placed on the lives and values of potential participants. It is important that clear information is provided about what the payment covers, and that the payment is linked to actual efforts, and does not depend on the participant remaining in the study until it has been completed (see FDA 2010).

As for the potential negative effects of payment on the relationship between the researcher and research participant or on the data the researcher receives access to, cultural and context sensitivity may be the primary solution to the problem. One option is to consult a sample of the population of participants in a project as to how to best promote trust and express respect in the relevant cultural context (Singer and Bossarte 2006, Lammers 2007).

Whether one fears increased commercialization of the research, a lessening of altruism as a motivation for contributing to society, or one is only concerned that finances will determine which research projects are feasible, it will also be important to examine other forms of recruitment than offering money.