This article is part of our The Z Files series.
There's been a lot of talk about the impact of a universal designated hitter, but mostly on the hitting side of the ledger. Lately however, the effect on pitchers, especially those of the Senior Circuit variety, has taken the spotlight.
There are two primary questions:
1. Are there specific hurlers earmarked for a greater of lesser adjustment relative to the average?
2. How do rankings adjust when facing a National League designated hitter is factored in?
Let's starter with the former, since it's necessary to investigate the latter. Data from the last three seasons will be considered. To be included in the study, a pitcher needed to face the equivalent of five innings against pitchers. There are 38 pitchers who satisfied that criteria each of the prior three seasons.
If it can be demonstrated individual pitchers' performance against pitchers each season is similar, then outlying 2019 numbers can be predictive of 2020 performance including a universal DH. That is, if a hurler's skills facing a pitcher were significantly better than the league average increase, he'll be hurt more by facing a designated hitter.
If it's predictive, skills derived from numbers with and without facing pitchers should be consistently better or worse than league average over the three-year span. Correlation will be used to test this, comparing 2017 to 2018, 2018 to 2019 and 2017 to 2019. If there is correlation, the results can be considered predictive. Random correlation suggests the skills exhibit variance, so trusting 2019 data in 2020 projections