From the Ad Hoc Committtee Report on the "Hockey Stick" global climate reconstruction (PDF) by Edward J. Wegman, David W. Scott, and Yasmin H. Said:
Two principal methods for temperature reconstructions have been used; CFR (climate field reconstruction) and CPS (climate-plus-scale). The CFR is essentially a principal component analysis and the CPS is a simple averaging of climate proxies, which are then scaled to actual temperature records. The controversy over Mann's methods lies in that the proxies are centered on the mean of the period 1902-1995, rather than on the whole time period. This mean is, thus, actually decentered low, which will cause it to exhibit a larger variance, giving it preference for being selected as the first principal component. The net effect of this decentering using the proxy data in (Mann, Bradley, and Hughes 1998 and Mann, Bradley, and Hughes 1999) is to produce a "hockey stick" shape. Centering the mean is a critical factor in using the principal component methodology properly. It is not clear that Mann and associates realized the error in their methodology at the time of publication. Because of the lack of full documentation of their data and computer code, we have not been able to reproduce their research. We did, however, successfully recapture similar results to (McIntyre and McKitrick, who published a critique of the "hockey stick" findings). This recreation supports the critique of the (Mann, Bradley, and Hughes 1998) methods, as the offset of the mean value creates an artificially large deviation from the desired mean of zero.CV of Dr. Edward Wegman.
Yasmin H. Said was a grad student of Dr. Wegman's, and has probably torpedoed his career by having his name associated with a document debunking a key tenet of the Church of Anthropogenic Climate Change.