Editor's note: On Tuesday, ESPN The Magazine released its Analytics Issue, with a cover story by Sam Miller about why baseball fans should embrace WAR (wins above replacement). We asked Keith Law to break down his "desert island stats," which are the metrics he can't live without when evaluating players.
Having a player's WAR (wins above replacement), even if you know which version of WAR it is, is not in and of itself terribly useful unless you know the breakdown of the numbers that went into it.
WAR is just the end of a process of normalizing different areas of a player's game -- for a hitter, that's offense, defense, and baserunning, with an adjustment for the offensive standards of his position -- so they can be added together into a single number.
Any system of valuing production should distill a player's contributions into a number that represents runs added/saved if it's a positive contribution and runs cost if it's a negative one. If you just have a player's WAR, you have no idea how he contributed to his team's success or lack thereof, and you can't assess the figure's reliability because you don't know how much came from, say, offense, which is one of the easiest things to measure accurately, and how much from defense, which is one of the hardest.