Hockey Stick

Canadian scientists Stephen McIntyre and Ross McKitrick uncovered a fundamental mathematical flaw in the computer program that was used to produce the “hockey stick”. In his original publications of the stick, Mann purported to use a standard method known as principal component analysis, or PCA, to find the dominant features in a set of more than 70 different climate records. However this was not true. McIntyre and McKitrick obtained part of the program that Mann used, and found serious problems. Not only does the program not do conventional PCA, but it handles data normalization in a way that can only be described as “mistaken”. This improper normalization procedure tends to emphasize any data that do have the hockey stick shape, and to suppress all data that do not. To demonstrate this effect, McIntyre and McKitrick created some meaningless test data that had, on average, no trends. This method of generating random data is called “Monte Carlo” analysis, after the famous casino, and it is widely used in statistical analysis to test procedures. When McIntyre and McKitrick fed these random data into the Mann procedure, out popped a hockey stick shape.


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