KEEPING a secret is hard work, as both common sense and past studies confirm. Omitting pertinent information from a conversation, or even intentionally misleading an interlocutor, requires nimble thinking. How much of a burden, though, is merely possessing a secret, rather than trying to defend it against a nosy questioner? The catharsis that often accompanies confessing guilty secrets suggests it may be quite large. But, until now, no one has examined the matter scientifically.

In a study just published in the Journal of Personality and Social Psychology, Michael Slepian of Columbia University, in New York, attempts to correct that omission. He and his colleagues presented a set of volunteers with a list of 38 sorts of things surveys suggest people commonly keep secret about themselves. Examples included infidelity, theft, poor performance at work, sexual orientation, having undergone an abortion and drug taking. Some of Dr Slepian’s volunteers participated over the internet. Some, recruited in New York’s biggest public space, Central Park, participated face to face. All remained anonymous—and, within statistical limits, both groups responded identically.

Dr Slepian and his team asked the volunteers whether, for each item on the list of potential secrets, they had never had the experience in question (and therefore had nothing to hide); had had it, but had not kept it secret; had had it, kept it secret for a while, but then let it out; had had it and kept it secret from some people but not from others; or had had it, kept it secret from everyone, and continued to do so.

For each secret that a participant currently kept, the researchers asked how often that participant found himself actively having to conceal it during conversations, and also how often he thought about it when not in the presence of someone from whom he was keeping it. They also asked participants to choose, on a 13-point scale of well-being, whether keeping a given secret had made life better or worse, with a “+6” indicating very much better, a “-6” indicating very much worse and a zero indicating that keeping the secret had no effect. They also asked a series of questions that let them construct an index of a volunteer’s health.

All told, the team found that 97% of participants kept at least one of the 38 types of secret in question, that the average person kept 13 secrets and that it was typical for people to have five that they had never disclosed to anyone else. The secret most often sequestered from the whole world was having sexual thoughts about someone other than an established romantic partner. This was followed closely by actual sexual relations with such a person. The researchers also discovered that people reported pondering their secrets privately about twice as often as they chose to conceal them from others—though there was much variation.

It was this private pondering, rather than the actual possession of a secret, that seemed crucial to health and well-being. People who reported thinking about their secrets less often than once a week over the course of the previous month had an average health index of 66 out of 100, compared with 49 for those who thought about their secrets every day. Similarly, those who thought little about their secrets had well-being scores close to zero, while those who thought about them a lot scored -2.

The types and numbers of secrets kept by members of these two contrasting groups, those who thought regularly about their secrets and those who did not, were not materially different. That their reactions to those secrets differed is therefore puzzling. Dr Slepian favours psychological explanations for the damage secrets do, such as the idea that they sometimes concern unresolved issues, which thus intrude on thinking. But that neither explains the different responses nor gets to the heart of the matter. If keeping secrets is beneficial—which, presumably, it often is—evolution might have been expected to have weeded out those who suffer as a consequence of doing so.

Perhaps such weeding is a work in progress, for deep secrecy of the sort people engage in becomes both possible and necessary only once language has come into being, and language is, itself, a recent evolutionary phenomenon. In the meantime, at least one human organisation has worked out how to benefit from the burden imposed by secrecy. The Roman Catholic sacrament of penance and reconciliation, commonly called confession, is a perfect response. It offers to lift that burden in a procedure that, though not cost free to the confessor is, itself, completely secret.