It should be no surprise by now that a ruthless focus on one number can lead investors down the wrong path. Yesterday Yum Brands' shares slipped backwards in spite of a decent set of results that met expectations without resorting to cosmetic tricks. The bad news: Chinese same-store sales growth was merely 4 per cent.

That metric gets more attention than it deserves because the world's largest restaurant operator, with more than 37,000 outlets worldwide, is heavily exposed to China. The bright signs of its KFC and Pizza Hut chains are one of the most visible indications of growing consumer appetites, and an early and aggressive push into the country means that Yum's 3,600 stores there produce almost two-fifths of the group's operating profit. By 2011 the US, where Taco Bell is the other highly profitable jewel in Yum's crown, will be the smallest contributor to profits after China and then the international division.

However, in China investors might be better off watching return on capital employed, consistently coming in at a mid-30's percentage level. Sales growth is affected by intentional cannibalisation in some areas, while pent up demand in new regions makes year one comps tough to match. But profitably growing a business in developing markets deserves credit. Rising Chinese wages might be a short-term threat to high levels of profitability in the country, but the improvement to middle-class incomes, not to mention a revaluing renminbi, will also help.