Monetary incentives to encourage people to live healthier lifestyles only work in the longer term when they are designed to stop negative behaviour, rather than promote positive choices, suggests new research from the London School of Economics and Political Science (LSE).

A paper published in Social Science and Medicine describes the results of a laboratory experiment where participants were invited to watch a series of videos while eating as many jelly beans as they liked. Partway through, incentives were introduced to encourage some participants to eat the sweets and for some participants to not eat the sweets for the duration of the next five minute video. For the purpose of comparison, another group of participants watched the video without an incentive. The experiment was then repeated two days later, when none of the participants received incentives.

Only the incentive to not eat sweets was found to still have an effect two days later. Participants who had been previously offered a £3 incentive to not eat any jelly beans ate significantly less sweets than the participants who had not receive a monetary incentive.

Matteo M Galizzi, an ESRC Future Research Leader Fellow and Assistant Professor of Behavioural Science at LSE, and one of the authors of the research, said: "Our findings are consistent with the idea that people find negative messages easier to retain than positive ones. Even though we only paid participants not to eat the jelly beans for five minutes, we seem to have primed them with the notion that not eating sweets is something good and this effect was still in play several days later.

"In the short run we know that incentives work, for example, in helping to motivate people to give up smoking. However this is the first time that research has directly compared what happens to differently designed health incentives when the incentives are removed. This is an important area of research because, in the real world, most incentives to get people to live healthier lives will not be able to be applied indefinitely."

A total of 353 people participated in 35 experimental sessions at the LSE Behavioural Lab.