Recent defenders of the quantity theory have undertaken the examination of more complex statistics than those concerned with the simple concomitance of quantity of money and prices. Two of these studies, the first by Professor Kemmerer[375] and the second by Professor Fisher, are so elaborate, have commanded such general attention, and have been accepted by so many students as conclusive demonstrations, that I feel it proper to give them detailed examination. I do this especially because highly important facts for our construction argument emerge from this critical examination. Kemmerer's and Fisher's studies reach high-water mark in the effort to give statistical demonstrations of the quantity theory. If they are invalid, then I know no other attempts which many students would suppose to be possible substitutes. The theory involved in both these studies is clearly stated by Professor Kemmerer: "A study of this kind, to be of any value, must cover the monetary demand as well as the monetary supply. Any test of the validity of the quantity theory consisting merely of a comparison of the amount of money in circulation with the general price-level is as worthless as would be a test of the power of a locomotive by a simple reference to its speed without taking into account the load it was carrying or the grade it was moving over." This criticism of many previous studies is, in general, I think, valid, though I should except from this list such detailed studies as that of W. C. Mitchell, who takes account, as far as may be, of all the variables involved, and who considers day by day and week by week changes. I think the older studies of Tooke,[376] may also be excepted. In point of fact, if one wishes to know how much reliance may be placed in the quantity theory as a basis for prediction, when one knows that money is increasing, the simple comparison of money and prices is a fair test. If the "other things" which must be "equal" are so numerous and complex that the quantity theory cannot manifest itself in a direct comparison, much of its significance _as a basis of prediction_ is gone.