To understand the study we should outline the basics first (and all of this and more is located in the "About DMB" section). Defense is broken down into three different ratings: Error Rates, Range, and Arm Strength (for Catchers and Outfielders). A defensive rating first lists the range of a player at a specific position and then the error rate. For example, 1987 Ozzie Smith's SS defensive rating is Ex / 40. This means he has "Excellent" Range and his error rate is 40% of an average shortstop. This is stellar, one of the best you will find in the game. The five ranges are Poor (Pr), Fair (Fr), Average (Av), Very Good (Vg), and Excellent (Ex).
Error rates are self explanatory and not part of the study. Any value over 100 is worse than average, any value under is better than average. A score 110, for example, means the player will yield 10% more errors than average.
It is the Range factor we are concerned with today. How exactly does this impact run scoring? How much better is Ex over Vg or how much worse is Pr than Av? The "study" ran 100 seasons for each change in defensive ratings. 100 seasons were ran where the defensive ranges for a team were set to Average. Then, 100 additional seasons were ran each position was changed. For example, the SS was bumped to Vg. Then another 100 bumping the shortstop up to Ex, keeping everything else the same. This was repeated for every position, changing only the range types of a particular position each time. A summary of the results:
Well, it's a lengthy summary, but what the above shows is as follows:
Catcher ranges have no discernable effect on run scoring
Pitcher ranges have very little effect on run scoring (836 to 843 Runs Scored Spread)
Infielders have a significant effect with the average Runs Scored spread ranging from 818 to 858
Outfielders have a great effect, but slightly less so than infielders. Spread of 823 R to 857 R
We need to take a step back and realize what this means. Using Bill James Pythagorean formula to determine "expected" wins based upon runs scored and runs against, a completely average defensive team (838 RS and 838 RA for example) can gain two wins in the standings by just improving their Third Basemen's range to Ex. The difference between a poor third basemen (Edgar Martinez) and a great one (Brooks Robinson) is even more pronounced - a whopping 4.5 games.
Now think about the effect of compiling a team with above average defense at most positions and the possibilities for a playoff birth should begin to fill your mind. Of course, defensive wizards tend to have a weak stick and the lack of offense needs to be taken into consideration too. One of the nice aspects of DMB is the ability to use defensive replacements, allowing an owner to substitute their offensive star for a defensive minded player late in the game.