Taken from an article on Grantland. I find this to be simplistic but accurate. Trade Value Rules 1. Contracts matter. Max Scherzer is a better pitcher than Gerrit Cole, but Scherzer will be eligible for free agency at the end of next season, while Cole isn't even arbitration-eligible yet and will be under team control through 2019. 2. Age matters. Bartolo Colon and Jose Fernandez put up fairly similar numbers in 2013, but Colon is 40 and likely won't be pitching for too much longer, while Fernandez is just 21 and could very well get better. 3. It's all relative. Pretend every team started shopping every player as a trade candidate. Who would attract the biggest return from any one of the other 29 clubs? For instance, if we're comparing the trade value of Paul Goldschmidt and Andrelton Simmons, we're not concerned that the Braves have an excellent first baseman of their own in Freddie Freeman, or that the Diamondbacks already have a promising young shortstop in Didi Gregorius. What we want to know is this: If every team were allowed to bid on Goldschmidt and Simmons, which player would net the greater return? 4. Positional scarcity matters. If a shortstop and first baseman put up comparable offensive numbers, the shortstop is the more valuable player, since it's much tougher to find a player with the defensive chops to handle short than it is to find one who can man first. That's already reflected in Wins Above Replacement (which you'll see referenced throughout these rankings), but it bears repeating. 5. Defense, park factors, and other variables not immediately apparent in superficial stats matter. These are not fantasy baseball rankings, so a player who hits 30 home runs isn't necessarily more valuable than one who hits 20, or even five. 6. Major leaguers only. Baseball teams place great value on top prospects, since those players offer the twin virtues of great potential and low price. But going through every minor league level for every team can muddy matters for non-prospect hounds. So we'll stick to players who have appeared in at least one major league game. That means Xander Bogaerts and Wil Myers are eligible for this list, but Byron Buxton and Miguel Sano (both of whom would otherwise be strong top-50 contenders) are not. 7. The list runs in reverse order. If Felix Hernandez is no. 20 on this list, it means the Mariners wouldn't trade him for anyone ranked 21 to 50, but would have to at least consider swapping him for the players ranked 19 to 1
