Posts From Other Folks: “Understanding Projections…” from Fangraphs

There was a good article at Fangraphs today that I wanted to point out because it has some applications to what is going on with this site here.  Their post was titled “Understanding Projections, “True Talent Level”, and Variability” and sought to explain a bit more about the world of baseball projections.  Nearly all of the research that is done on this site during this time of year is directly tied with analyzing the Marcel, CAIRO and ZiPS projection systems.  Each of those systems represents its own little universe of players with expected highs and lows and we take a peek inside those worlds and see how any given player is expected to do in comparison to the others.  But, this article points out some words of wisdom that I’d like to highlight:

Most people get into projections as a result of fantasy baseball, so this makes sense; we all want to know which player is going to hit 30 homeruns this next season and which will steal 40 bases. However, projections are actually measuring something different than a player’s expected production: they’re measuring a player’s true talent level

Let’s start with something simple: flipping a coin. We’d expect that a normal coin would have a “true talent level” of landing heads 50% of the time, right? If you flipped that coin 100 times, though, it may be that you’d end up with 53 heads and 47 tails….or with 45 heads and 55 tails. You’d be most likely to end up with a result close to 50/50, but it’s no guarantee that things would end up precisely at the coin’s true talent level every single time.

This important analogy highlights something that must be clear when using the projections within these cheatsheets or when looking at my analysis on the site.  The projections are not necessarily predictions of exact stats but a prediction of expected level of performance.  That may sound like a small difference but can really be quite large.

The article gets into a bit of math about standard deviations related to predicted talent levels then goes into this paragraph:

In other words, say we project David Wright to hit 20 homeruns this season. That projection isn’t saying that he’s going to hit exactly 20 homeruns, but instead that he’s 68% likely to hit within one standard deviation of 20 homeruns. With that in mind, Wright hitting either 15 or 25 homeruns wouldn’t necessarily prove the initial projection “wrong”: it just means that Wright’s season varied from his projection, and we can use that information to better project his true-talent level going forward.

A tiny bit of variability among players can greatly shake up the whole balance of power in fantasy baseball even. There’s quite a big difference in value if Player X and Player Y are both projected for 20 homeruns but X hits 15 and Y hits 25.  In that scenario, the projections weren’t necessarily “wrong” as the players were still within their true-talent level but a 10 HR difference goes a long way between winning and losing in fantasy baseball.

So the next time you start looking through projections, remember to take variability into account. Our minds love to eschew probability and uncertainty – why do you think casinos make such a killing? – but understanding this concept can keep you from drawing faulty conclusions from projections. Embrace uncertainty, and it might help you beat the house (or beat your friends at Fantasy).

Variability is expected and projections are purely meant to show safe bets about future performance based on past performance.  They are a representation of assumed talent level and shouldn’t be looked at as absolute certainties.  In the end, the projection systems represent a good starting point but also remember to use your gut and your own knowledge to help differentiate similarly valued players.

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