Mookie published an article about UFC 173 where Meltzer was using Google Trends data as a proxy for PPV buyrate. In order to figure out if it's a decent proxy it, I calculated their Pearson Coefficient. Gathered data from MMA Payout and Google Trends.
Cleaned up a bit, here's what it looks like.
The % of peak searches is split where there is more than one PPV in a month. The uniq tab removes all events in a month where there is more than one PPV.
The Pearson's Coefficient is 0.7208 for all events and 0.7693 for the unique in month events. This means that 77% of the variance in the buyrate is captured by the Google Trends data, making it a good but not exceptional proxy. Even this happens to be great news for UFC 175, as this July is the largest spike in the trends data since UFC 100.