I'm gonna turn this one over to the Cafe.
Andy's recent series on under-appreciated players left me wondering if there was a systematic way to find under and overrated players. In theory if we would could compare every player's perceived value to his actual value, we would have the information we need to do a complete evaluation of the players whose value and reputation we worlds apart. Fortunately Baseball-Reference.com has both objective and subjective rankings.
WAR is the Baseball-Reference.com attempt to use a single value to rate each player. All aspects of the game are taken into account and there is no room for opinion or popularity in creating these rankings. It is completely objective.
Conversely, the EloRater from that site is subjective. Readers are asked to compare two players and determine who was better. The results of all votes are then combined to create a list of greatest players. While player stats are used in this process clearly the results of these comparisons are based on perceptions and reflect the regard in which players are held.
Comparing these two numbers, would then provide us with the information we are looking for. Players who do much better in the EloRater then their WAR would suggest are overrated, while those who do much worse would be underrated.
For example, as of this writing Joe Carter has earned 1873 points in the EloRater, which is the 279th best among retired position players. Meanwhile his career WAR is 16.5 which is the 822nd best. This tells us that he is ranked 279-822= 543 places above where he should be, which is quite an overrating of his value.
In fact, Carter is the 6th most overrated retired position player in baseball history.