GMAT Hacks
Amazon author page
College Splits
Heavy Topspin
Tennis Abstract
The Summer of Jeff

Jeff Sackmann is an author and entrepreneur best known for his work in the fields of sports statistics and test preparation.

Jeff has long been a driving force in the collection, dissemination, and analysis of baseball statistics at the college and minor league levels. With Kent Bonham, he founded College Splits, which gathers box scores and play-by-play data for every Division I college baseball team, plus plenty of D-II, D-III, and NAIA teams. More than half of MLB teams are happy customers.

From 2006 to 2010, he ran Minor League Splits, a website that displayed the potential value of play-by-play-based statistics at the minor league level. The site's data is now available to the public.

For nearly a decade, Jeff has written extensively about baseball at all levels. He writes a weekly column for ESPN Insider during the college baseball season, and has contributed to The Wall Street Journal, The Hardball Times, and Baseball Prospectus, among others. He has provided stats and commentary for ten baseball books, including the Graphical Player series, and has appeared on radio shows ranging from podcasts to NPR's Morning Edition.

Over the same time span, he has built GMAT Hacks, a valuable resource for potential MBA candidates. GMAT Hacks features hundreds of free articles and several instructional videos to make the test-prep process more efficient and less stressful.

Jeff has written several GMAT textbooks, which are available in a variety of formats. The flagship book is Total GMAT Math [PDF | print], a comprehensive overview of the GMAT Quantitative section. It is matched by Total GMAT Verbal [PDF | print] and supplemented by a strategy guide, GMAT 111 [PDF | Kindle | print].

In addition, he has created a set of 1,800 practice GMAT math problems [PDFs], which are available in sets of 100 according to subject matter and difficulty level. He has also published explantions to all of the math problems in the Official Guide to GMAT Review [PDF | HTML]. Jeff is widely recognized as an expert on creating realistic practice material, and has worked with several GMAT companies to develop and improve their student resources.

More recently, Jeff has begun investigating professional tennis from a quantitative perspective. He has created the statistical reference site Tennis Abstract and he publishes his tennis research at Heavy Topspin. He has also provided tennis stats and contributed articles on tennis to The Wall Street Journal and

He has created a predictive tennis ranking system that outperforms the official ATP and WTA rankings. He has also published a great deal of work on the subject of win probability, including graphs and stats for more than 600 matches. Some of his code is available on GitHub.

In August 2011, he gave a talk at the Longwood Cricket Club in Massachusetts entitled, "The Present and Future of Statistics in Tennis." Video of the presentation is available at Vimeo.

Before pursuing sports statistics and test preparation, Jeff was a professional saxophonist and bandleader. He performed with a variety of groups, including his own Oy Christina! jazz orchestra and James Brown's original "funky drummer," Clyde Stubblefield.

Four of his albums are available on Bandcamp, including two with his 15-piece jazz orchestra. He has published many of the complete charts, as well.

From September 2011 to June 2013, Jeff was a full-time traveler, visiting 60 countries and all seven continents. He promises not to write a book about it.