Mark J Penn has advised Hillary and Bill Clinton, Bill Gates and Tony Blair on the way the world is heading. Now he sees potential for a McDonald's of tattoos. With "standardised brand, safety assurances and national advertising", it "could double the market overnight". Doubtless to the horror of all parents of teenagers, Penn has the figures to back his hunch. In three years, the number of tattooed Americans has risen from 20 million to 30 million. Equally perplexing for some of us, the number of American adults who sleep less than six hours a night has crept up from 12 per cent in 1998 to 16 per cent in 2005. Penn specialises in the counter-intuitive. Though American women are on average 25 pounds heavier than they were 40 years ago, there has never been such demand for "petite" sizes (for women under 5ft 4in). Women are living longer, hence they are growing shorter, and new US immigrants, mostly Asian and Latino, are 2-3 inches shorter than the average American woman. A microtrend that involves 1 per cent of the population may seem insignificant, but Penn says we should be in no doubt about the potential power of such numbers. If al-Qa'ida persuaded 1 per cent of Muslims to join, it would have 10 million members. Marketers will read this book and politicians ought to.