The Houston Astros are better than the Texas Rangers. At least that is what one would gather from reading any analytic article written about the Rangers lately. The main reason appears to be that the Rangers have been extraordinarily lucky over the first three months of the season.

According to Base Runs, currently the run estimator of choice for sabermetricians, the Rangers have benefited from roughly 27 runs of cluster luck. Cluster luck is when a teams run differential varies greatly from their estimate. Combine that with the fact that they have outperformed their Pythagenpat (win estimator used on Fangraphs) record by 6 games, and the Rangers “should” have a record of 39-36. Or should they?

Base Runs are calculated by using the season totals of a team’s component statistics. That is not the way runs are scored, however. In reality, a home run that you hit in the 5th inning has no affect on a single you hit in the 2nd. Runs are scored at the inning level. By using season totals you are basically saying that, given an inning of 75 games worth of outs, the Rangers would score roughly 341 runs and allow 323. That introduces a potentially huge source of error.

The following table shows the Rangers’ actual run differential, the Base Runs run differential found by adding up the components over the entire season, and the Base Runs run differential found by adding up the components in each inning.

Actual BsR Season BsR Inning +45 +18 +26

According to the table, the Rangers gained 8 runs by calculating Base Runs at the inning level compared to the season level. Now by adding the expected run totals for each inning, the expected scores for each game can be calculated and credit for a “win” can be given to the team with the higher estimate of runs scored in each game and a “loss” can be given to the team with the lower estimate of runs scored in each game. I will call this win estimate “Component Wins.” The following table shows the Rangers actual record, their Pythagenpat record using actual runs, their Pythagenpat record using Base Runs, and their Component Wins.

Actual Pythag – Actual Pythag – BsR Component Wins 48-27 42-33 39-36 45-30

This table shows the Rangers HAVE been lucky this season…by about 3 games. The Rangers have outperformed their expected run differential in 42 of 75 games this season, but the difference was only enough to change the expected outcome (changing an expected loss into a win and vice versa) 12 times. The Rangers are 7-5 in those games, meaning they won 7 games they should have lost and lost 5 games they should have won.

So it does appear that the Rangers have been slightly lucky this season. Enough to move them from first place to…first place.