Is Year-to-Year Hitter Consistency Consistent?

Whether I like it or not, I’ve opened Pandora’s box on year-to-year consistency. The concept states that if a hitter’s overall year-to-year production is consistent, the consistent production will continue. Therefore, good, consistent hitters should be valued more highly since owners know what they’ll be getting on draft day. The problem is that consistent overall production doesn’t lead to future consistency.

The discussion started last week when I wrote that Eric Hosmer and Edwin Encarnacion had similar fantasy values but Hosmer’s NFBC ADP (average draft position) was quite a bit lower. Reader’s stated in the comments they devalued Hosmer because of his year-to-year inconsistency.

Now, some readers disagreed with the pair’s overall value because of different stances on their projections. Some valid arguments exist on the projections but it is a discussion for another day. The focus now is on year-to-year consistency being predictive of future consistency.

The discussion continued Friday on Twitter with several industry experts weighing in. Just expand the replies and read away on the hundred or so comments.

Consistency suckkkks! I know this guy agrees with me ? @RyanBHQ#FPAZ17 https://t.co/gwoYzDhABL

— Derek Carty (@DerekCarty) January 26, 2018

Two main camps emerged. Those experts who find consistency at the beginning of draft important and those that don’t care about consistency at all.

In the above Twitter thread, some in-season consistency was discussed. If readers want to read up and understand about in-season consistency, start with this article (and the ones linked from it) by Bill Petti at the Hardball Times. He sums up his findings as:

Hitters that tend to hit the ball in the air for power tend to produce in a more volatile fashion, while groundball hitters with higher on-base skills appear to produce more closely to their average on a daily basis.

He’s posted his daily volatility (consistency) values going back to 1974 for those interested. Enough on in-season numbers and on to the year-to-year discussion.

It’s time to determine if consistent hitters remains consistent. Here are the parameters I used.

To measure player talent, I’m going with OPS. While some other measures (e.g. wOBA or wRC+) are probably a better measure of true talent, OPS is easy to find and calculate. For the consistency metric, I took the standard deviation of the OPS values in question. The higher the deviation, therefore the less consistent the player. For the player’s talent level, I’m using OPS weighted by his plate appearances from X previous seasons (wOPS).

Note: Please let me know if you want to see other stats, benchmarks, seasons instead of the following ones used. Depending on the ease of manipulating the data, I can get back with an immediate response or I may take several responses and group them into a future article.

Math for those who care. Findings in summary for those smart enough to skip this section.

To start off the analysis, I took three seasons of data with minimum 100 PA in each and compared them to the next season. I cut-and-diced the data several ways to see if I could find any patterns of consistency. I found almost nothing.

First, I started out with the regulars who averaged 400 PA in the previous three seasons and compared their three-season deviation to the absolute difference between wOPS and actual value. The r-squared was .0005. Not good. Using this same set of players, I took the 50 least and most consistent hitters and compared their wOPS and the actual 4th-season values. The most consistent hitters averaged an absolute difference of .07232. For the least consistent hitters, the value was .072333. Nothing so far.

To see if better hitters or worse hitters were more consistent, I divided the group into two by wOPS and ran the same analysis. The r-squared jumped to a still pathetic .0035 for the more talented group and was .00074 for the less talented players.

The talented group’s average absolute difference is .0589 for the least consistent hitters and .0784 from the volatile. Now, a 20-point difference is decent. More on this in a bit but first, the weaker hitters. The least consistent group’s absolute average difference from actual OPS and wOPS is .0912. For the most inconsistent bad players, the average is .0775 for a ~14-point difference but in the opposite way compared to the good hitters. None of the data is consistent. Good, consistent players remain consistent but bad, consistent become inconsistent. I don’t buy it. I’m going to keep the results as reference and move on to find any possible pattern.

Even though I took the players with an average number of plate appearances over 400, those with more plate appearances were more consistent. The more data available, the better the outcome. The top-50 consistent hitters averaged 554 PA while the bottom-50 consistency players were only at 496 PA. By comparing the standard deviation in PA to OPS, an r-square of .05 emerges. While not great, it’s the best correlation produced so far. It’s not surprising since the more plate appearances a hitter gets, the more likely they are to be near their true talent level each season. With fewer at-bats, the more likely variation will occur. This factor is a major consideration going forward.

First, here are the r-squared values between different datasets (all available here to analyze).

No values or trends of interest in that table. I’m throwing in the towel for today. No more math.

Summary

For those who skipped the math, congrats. Here’s the only points.

• There is little-to-no year-to-year correlation with consistency when just using OPS as the input for consistency.
• If just using OPS, playing time does matter. Hitters with the most plate appearances are the more consistent because they’ve had more chances to reach their true talent level.

Again, let me know if any other parameters could be changed to consistency predictable.

Does this mean year-to-year consistency isn’t predictable? No, not close. As I was working on the analysis, I kept going back to Bill Petti’s day-to-day correlation studies. It’s not the combined values but the overall talent inputs. Plate discipline and contact stabilizes quickly while BABIP and ISO don’t. While I have it run the numbers yet, I would not be surprised if player types (e.g. high K% sluggers) need to be the focus for consistency. It almost makes too much sense now. Stay tuned to find out if the idea is true in a day or two.