Stephanie Kovalchik, data scientist at Tennis Australia's Game Insight Group, on comparing the Roger Federer of 2017 with the Federer of 2015, and comparing Serena Williams with the men's field. Produced and edited by Jorge Estrada, with music by Lee Rosevere. Kovalchik on Federer: http://on-the-t.com/2017/07/28/federer-2017/ Kovalchik on Williams: http://on-the-t.com/2017/06/27/serena-defense/ Kovalchik on Twitter: https://twitter.com/StatsOnTheT