Trials show that people who think they\'ve done something healthy, even if they haven\'t, smoke more and believe they are invulnerable to diseases, this was published at the \'\' Gaurdian\". In the study of risk perception, people talk about \"the licensing effect\": when you take a vitamin pill, for example, you think you\'ve done something healthy and wholesome, so you permit yourself to eat more chips and have a cigarette. It sounds like a nice idea, but a bit vague. Two new experiments put flesh on these bones. Firstly, researchers took 74 undergraduates who were daily smokers, and divided them into two groups at random. The first group were given a dummy pill, a placebo, and were told just that: you\'re in the control group, taking a dummy pill, with no active ingredient. The other participants were in the vitamin pill group: you\'ve been given a vitamin pill, they were told. But in fact, the researchers had lied. Everyone in the study got the same dummy pill, with no active ingredient. Half of them thought they\'d had a health-giving vitamin pill, because the intention was to see whether people\'s health behaviours change if they think they\'ve had a nice, healthy vitamin pill. After the pills, they were given a survey to fill out. Because it was Taiwan, where lots of people smoke, they were told: \"This survey will take you about one hour to finish … you\'re allowed to smoke if you want.\" The results were startling. Firstly, people who thought they\'d had a vitamin pill gave different answers on the survey. These featured questions from the excellently titled Adolescent Invulnerability Scale (which has been reasonably well validated elsewhere), such as \"Special problems, getting an illness or disease, are not likely to happen to me\", \"I\'m unlikely to be injured in an accident\", and so on. People who thought they\'d had a vitamin pill rated themselves as generally more invulnerable.