Page:Stabilizing the dollar, Fisher, 1920.djvu/71

. 5] a general survey, as we shall see, fails to confirm many, if any, of the numerous popular impressions which have gone abroad.

5. The Argument from Probability

All those who have offered such explanations make one fatal mistake. They look at the wrong side of the market. They seek the causes wholly in the goods, the prices of which have changed, and not at all in the gold dollar, in terms of which those prices are expressed.

Which of these—goods in general, or the dollar in particular—is the more likely to vary? Is it credible that commodities should rise and fall so concertedly without some simple common cause? Is it not more probable that the dollar, which, as such a common cause, affects all the commodities it buys, should fall in value than that hundreds of individual changes in the values of other commodities should all happen to occur in concert? Are not the coincidences involved a little too remarkable? It is one of the accepted maxims of logic that a complicated multiple explanation is not to be presumed if a simple single explanation can be assumed.

Mere chance almost never plays onesidedly. If we throw nine coins in the air, it will not surprise us if four or five of them come up heads, but it will surprise us greatly if all come up heads. The chance of such a coincidence is exactly 1 in 512. The chance that eight would come up heads is less than 1 in 50 (exactly 10 in 512).

Now, of the nine groups of commodities included in the index number of the United States Bureau of Labor