How valuable is a top prospect?
The above chart shows each of Baseball America’s Top 100 prospects who were listed as position players, as well as their Wins Above Replacement (Baseball-Reference.com version) in their first seven seasons, roughly corresponding to the period of team control before free agency. The most striking feature of the chart is the variance — top prospects tend to be more valuable, and the collection of “busts” around 0 WAR increases as the ranking gets worse, but the outcomes vary considerably throughout the spectrum.
The best-fit line shows a logarighmic relationship between ranking and expected WAR (i.e., WAR varies with ln(rank)). A top-ranked position-player prospect is expected to be worth almost 20 WAR in his first seven seasons, while a #100-ranked hitter is expected to be worth less than 5 WAR.
Albert Pujols (ranked #42 in 2001) is the lonely outlier at the top of the chart. Jeff Bagwell (#32 in 1991), Chase Utley (#81 in 2003) and Ichiro (#9 in 2001) are the others above 40 WAR.
The upside is a bit lower for pitchers, but the variance remains — the ranking-WAR relationship is even weaker than it was for hitters (R-squared = .05 for pitchers, .10 for hitters). A #1-ranked pitcher is expected to be worth about 12 WAR in his first seven seasons, while a #100-ranked pitcher is expected to be worth 3 WAR. (Only three pitchers have been ranked #1 since 1993, most recently Daisuke Matsuzaka in 2007.)
Roy Oswalt (#13 in 2001) is currently the most valuable pitcher on this graph, though Clayton Kershaw (not pictured, but #24 in 2007 and #7 in 2008) should edge him by the end of this season, his seventh.
Combining the two groups, we see that top-100 hitters tend to be worth more than top-100 pitchers, most notably at the very top of the rankings. A #1-ranked pitcher projects to be worth about as much as a #10-ranked hitter — but the expected value of hitters drops more quickly than the value of pitchers, suggesting that hitters may be easier to rank than pitchers.