Motivation

The first and most obvious question is "Why?", as in why do I care how consistent a player has been?

There are three main reasons why I think this tool is valuable.

1. So often there are debates over the best player in baseball or best at a certain position. For example: who was the best offensive second baseman of the last 40 years--Joe Morgan, Ryne Sandberg, or Jeff Kent? I don't find this type of debate particularly useful. When viewed at least from purely a statistical standpoint, there isn't a team in baseball that wouldn't have been happy to have any of those guys playing for them. They were all very good players. I'm more interesting in knowing how reliable given players were. For example, Jeff Kent put up 377 homers in career while never hitting more than 37 in any one season, while Ryne Sandberg totaled only 282 homers, hit 40 in one season, and never hit more than 30 in any other season. My gut feeling is that Kent was a more consistent player, but I'd like to have a tool to measure that carefully.

2. I'm curious to be able to quantify how big of an abberation certain seasons were for certain players. The classic example is Brady Anderson's 1996 season when he hit 50 homers despite never hitting even half that in any other year of his career. Another example is the one I gave just above--was Ryne Sandberg's 40 HR season a major aberration or just a small one? At the time, could we have counted on Sanberg to reproduce that type of season? Same goes for Mark McGwire's 1991, when he batted just .201 and hit only 22 HR in 154 games. I want to quantify just how terrible that season was compared to his average year.

3. As I have already run a whole bunch of these numbers, I've seen a couple of trends emerge that I think will prove very useful. First is that players often take a few years to mature. When quantifying their first few seasons, there is very often a 'learning curve' where the total quantified performance builds up to a plateau that they typically reach in their 3rd or 4th season. Second is that there's a downward ramp that starts later in their career until finally their performance trickles off so much that they end up retiring, voluntarily or otherwise. I think that these trends can be used as a predictive tool by understanding typical career trends.

As you'll see over time, the numbers can be presented graphically for each player's career, making it easy to see trending that is upward or downward, as well as highly aberrant years. Much more to come on this.