I just read an article from Dylan Murphy at sportsgrid.com looking at the accuracy rate of NBA reporters for reporting rumors at the trade deadline. He looked at the rumors reported by Adrian Wojnarowski, Chris Broussard, Marc Spears, Marc Stein, Sam Amick and Ken Berger, comparing the number of reports to the number of deals that actually came to fruition.
The results, unsurprisingly, were dismal. Spears had the best hit ratio at 40 percent, but he also had the smallest sample size — with two of the five rumors he reported actually going down.
In fact, the hit rate was pretty much a function of the sample size — there’s a statistical function called r-squared that measures the extent to which the y values in a set of x-y data pairs are influenced by the x values. Put the number of predictions on the X axis and the hit rate on the Y axis and calculate r-squared — the result in this case is 0.96596, or close to 97 percent. This is very high indeed — a perfect correlation is 1.0 or 100 percent.
So Murphy’s article doesn’t measure how accurate the reporters are at all — it measures how many rumors they report. Continue reading