Since the introduction of Sabermetrics many concepts and terms have started to enter the main stream. OBP is now a regular on the NESN broadcast and OPS is often a common term in any presentation. That has not led to a change in much of the conventional wisdom that we have started to be seen as not true. Just watch a few minutes of the ESPN Wednesday night game and by the third time you hear Joe Morgan call for a bunt you’ll know what I’m talking about.
One common misconception to me that would make player analysis much better is the understanding of streaks and slumps. To put it quite bluntly there is no such thing as a streak or a slump. There may be peaks and valleys in any given season, but that doesn’t mean you’re doing anything different.
Bill James wrote about this in one of his earlier papers Understanding the Fog. He said that there was no hot or cold streaks, but simply a cluster of events that made it appear to be on or the other. The point was the placement of them was completely random.
Another way to think about this of course with all statistics is gambling. No matter the game you play; poker, blackjack, roulette, etc, you have a certain chance of winning and losing. If you win or lose a larger number of chances on a “run” it’s inevitable that you will return to normal averages if you continue to play. You could flip a coin 1000 times and while you may have several periods when you get the same result in the end you should be very close to 500:500.
There are many reasons to keep this in mind. The first is to never assume a player is one end or the other when a streak happens. Jason Bay was neither the player who had an OPS of .689 in July or a 1.123 in April. He was the player who finished with a .921 OPS in 2009. This is very important for talent evaluation and fan expectations.
The next reason is making managerial player decisions based on things like slumps and matchups. Over the past few years fans have had access to more numbers than ever and some of the worst numbers are things like last 7 games or matchups. If a player has hit over .500 with an OPS over .600 in his last 7 games it will have no effect on the next game or AB. The same goes for someone who has gone 5 for 5 against the current pitcher.
As a scientist I regularly frequent the Science Blogs and I recently found this post from last year on The Frontal Cortex blog there. The central argument is actually looking at basketball and the hot hand, but also takes a look at Joe DiMaggio and The Streak. While many think this was so far outside the normal variance of results there is evidence that this length of a streak should have occurred in the history of the sport at some point.
The streaks ranged from 39 games at the shortest, to a freakish baseball universe where the record was a remarkable (and remarkably rare) 109 games.
That doesn’t mean that the streak was a sure thing as most of the streaks occurred before the 40’s and an amazing 300 of the streaks were accomplished by a fictional Ty Cobb. This is just showing that it was something we should have expected and wasn’t a sign of increased talent during the streak just an extreme “run” of positive outcomes.
Perhaps I should mention that while I don’t believe in the traditional slump or streak there are always outside forces. Bay also was in a slump in 2007 that lasted nearly his whole season, but that was attributed to injury. This is usually the case as a slump could have evidence to explain it, but a “hot” streak cannot.
So, what can we learn from this? That no player should be labeled as “streaky” as though it’s a bad thing. There might be players who are a bit more variable, but no one is really streaky. A player who relies on the three true outcomes (homer, walk or strikeout) might appear more “streaky” as his perceived value results mostly from homers. If these homers are bunched then his value to the team appears more “streaky”.
In conclusion we can’t stop Boston.com from labeling every time someone goes 4 for 4 in back-to-back games as a “hot” streak, but we can realize what is actually going on. The streak is nothing more than random variation and we need to look for the true talent level.