What teams want most out of a top prospect is production in the first six years of service time, before he hits free agency. Comparing performance over that time for traded prospects to non-traded prospects can show whether the two groups trace different paths in their post-prospect careers. (Determining a given player’s first six seasons involved finding the year the player cleared his rookie innings or plate appearance threshold and counting five years into the future. It’s a rough estimate of pre-free-agency service time, but it works as a close approximation across the sample.)

The first finding of note is that prospects of all flavors bust: More than half of all top-50 prospects in this sample accumulated less than 6 WAR in their first six seasons, and even top-10 prospects—the best of the best—failed to record even 1 WAR per season more than a third of the time.

But within that broader result, a trade-centric pattern emerges. Through their first six MLB seasons, the non-traded prospects accrued an average of 27 percent more WAR than their traded counterparts, with sizable advantages for both pitchers (who saw a 25 percent gap) and position players (31 percent). It’s a statistically significant difference, too, which suggests that the discrepancy stems from a real effect and not mere chance.

This effect matches one Ben Lindbergh found in 2012 when looking just at top-10 prospects: Those who are traded tend to underperform compared to those who aren’t. Mashing hundreds of players into one average might not be the best way to judge success, as prospects produce a wide range of outcomes, but the most obvious differences between the two groups appear at the extremes.

On the most disappointing end, 28 percent of traded prospects were worth negative WAR over their first six seasons. That’s a huge number—just 18 percent of non-traded prospects can say the same—and another 29 percent were worth between zero and six WAR, which says that a fan base excited about a touted youngster joining its farm system has almost a three-in-five chance of its new favorite becoming a bit player or worse.

And on the most successful end, traded prospects were three times less likely to develop into stars than their non-traded counterparts. Just 2.9 percent of traded players accumulated 24-plus WAR over their first six seasons (or 4-plus WAR per year, meaning consistent All-Star-level production), versus 8.8 percent of non-traded players, and a gap appears in the 18-24-WAR group (3-4 WAR per year), too.

Boston couldn’t have added Chris Sale without losing Yoán Moncada, who was a month away from being named BA’s no. 2 overall prospect, and Michael Kopech (no. 32). And the Cubs couldn’t have added Aroldis Chapman and José Quintana without losing Gleyber Torres (no. 5) and Eloy Jimenez (no. 4), respectively. That the highest-profile prospects traded in recent seasons came from Boston’s Dave Dombrowski and Chicago’s Theo Epstein isn’t a coincidence, Paternostro says—those executives have the reputation and job stability to take risks. For the average GM, though, “If you miss on that trade, it’s kind of a PR nightmare with your fan base now, because they can click one button and get reports on these guys and go, ‘Oh, you idiot, you traded Eloy Jimenez. BA or BP says he’s a likely above-average regular, potential All-Star.’”