http://www.jssm.org/vol4/n4/17/v4n4-17pdf.pdf
RESULTS
...While the majority of the data in Table 3 have
not been previously reported, some data does exist.
Differences in Table 3 values versus the reported
values can be attributed to differences in subjects as
well as analysis methodologies, and the clubs used.
In all cases the reported data is for a few subjects
only. For example, the magnitude of the grip
velocity agrees well with Vaughn (1979),
however
there was not the significant reduction in hand speed
prior to impact as reported and which is also
discussed by Cochran and Stobbs (1969). The
maximum club head velocity values and velocity...
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PS... That above reference paper by Nesbit et al is a good example of how a technical paper should be written for publication is scientific journals. The reference Bigwill presented is a good example of a report written to promote a business; especially one being written to to appeal to the current zeitgeist. That he (seems to) advocate "X-factor" says it all to me... But to each their own.