"Mr Balin helps crack that problem. In the first few seconds a visitor spends on SmarterTravel’s site an algorithm builds a picture of them. Click speed helps: window-shoppers tend to skip quickly between pages, serious buyers ponder for longer. Other data including the time of day, number of previous visits and location are important. The algorithm spits out the probability that the user is a potential buyer. With that, it calculates the revenue gains and risks (of distracting shoppers) associated with showing adverts. The site is adjusted in a few milliseconds."
Damn that's crazy.
Writing software that involves risk×reward estimation makes one an economist? Nice try, Economist! Whether to display ads may be an economic decision, but no more than the color scheme or the logo; some economists are so desperate to regain respect for their field, they'd claim the sun as their own if it didn't have such a hopelessly unprofitable business model.