The problem, the researchers found, is that the evidence presented in any one study was usually weak.

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Third quarter is usually the seasonally weak month but crop nutrient prices remained firm during the summer months because of a tight global supply and strong restocking demand in the northern hemisphere.

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Countries like to influence their neighbors, and large and powerful countries that are surrounded by small and weak countries are usually capable of doing this.

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An under-hit back-pass from Michal Zewlakow let in Healy five minutes later but the usually deadly marksman struck a weak shot which was kept out by Celtic keeper Boruc before the ball was scrambled away.

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After all, central banks usually cut interest rates in response to weak demand and low inflation.

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Governments usually manipulate exchange rates to make their currencies artificially weak, not strong.

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But it is still considered weak as India's industrial production has usually grown at least 5% in recent years till 2011.

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As you'd expect, spreads usually widen for companies with litigation problems, heavy debt loads or weak operating results.

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What these notions usually have in common, besides a snappy concept and a persuasive spokesperson, is a weak scientific foundation.

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