aeRatio – A true measure of RBIs

With each player coming up to the plate over a course of the year, they will all have unique situations due to their spot in the lineup and surrounding teammates.  Some players are faced with more opportunities to drive in runs than others, some RBIs are driven in much easier, and some players just have more total at bats in general--so why should a player’s ability to drive in runs be compared using only a simple tally of the runners they cause to score?  By creating the measure of Expected RBI, you are able to find how well a player drives in runs in relation to the situations that they were presented.

In order to do so, you need to calculate:


Using Retrosheet, all of the above data is available to calculate.  Multiplying the outcome percentages with the RBI created percentages by the number of ABs in a given situation will give you a player’s expected RBI for that situation.  Repeat for each situation for their total expected RBI that season.

Also using Retrosheet, you can find a players actual RBI in each of these situations during a season.  Once a total actual RBI and expected RBI are found for a player, simply divide the actual RBI by expected RBI to get their aeRatio.

Please refer to the links and the glossary for any further explanation.  Also, check in on the expansion page as I include tips and expansions on the database.

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