One of the most telling revelations in Tony Blair's autobiography “A Journey” last week was how he coped with the daily stress of dealing with Gordon Brown: "Stiff whisky or G&T before dinner, couple of glasses of wine or even half a bottle with it. So not excessively excessive. I had a limit. But I was aware that it had become a prop." Judging by the comments in the press, many people were surprised that he thought this amount of alcohol was worth mentioning at all. So what does this tell us – is the nanny state interfering in a harmless pleasure, or are we deluding ourselves into thinking that excessive drinking is “normal”? Surveys into drinking patterns are complicated by the so-called “under-reporting” effect – where we consciously or unconsciously understate our true consumption. Similar effects have been observed in calorie-counting (“I only eat lettuce and still put on weight”) and even voting intentions, where opinion polls significantly underestimated the Conservative vote in 1987. In most instances it’s hard to measure the extent of under-reporting. Interestingly, in the case of alcohol, there is a reliable source of total consumption – since it is carefully measured and taxed. This allows us to compare the “bottom up” (or should that be “bottoms up”?) aggregation of survey results with a “top-down” estimate of annual sales derived from HM Revenue and Customs data. In 2007, the Office of National Statistics commissioned research to estimate alcohol consumption revealing that, on average, the sample population admitted drinking 14.6 units per week. According to analysis of Revenue and Customs data by the British Beer and Pub Association (BBPA), UK adults consumed 9.2 litres of pure alcohol per head in 2007, equivalent to 920 units over the year or 17.7 units a week. These findings suggest that we understate our consumption by around 20% on average. Why do we do this – is it embarrassment, self-delusion, or confusion with measure sizes and alcohol strengths? That’s a different question – worth thinking about when you’re trying to work out if your glass is half-full or half-empty!