The latest research suggestion is that a person who smokes one cigarette is twice as likely to go on to smoke a few more than another person who smokes one cigarette. (I simplify the maths for blog-effectiveness, of course. But not the logic.)
I’d have thought that most people (usually kids) who decide to try a cigarette (or anything else dangerous, for that matter) do so either because they are peer-pressured to, or because they want to, and will probably go on to try a few more, at least ‘for a period’ (undefined). The detailed commentary on this ‘research’ does make this qualifying point among several others – for example, that it was a self-selecting sample drawn from widely variant populations and can therefore be considered as, at best, ‘only an estimate’ – but that doesn’t stop the journalists (I’m drawing on the reports in the Guardian and the Times) from headlining this as if it’s in any way factual or significant.
I have no axe to grind here, as I stopped smoking several months ago and don’t intend to start again. I’m just against spurious science.