Bobby Abreu's owners from two years ago -- heck, since then, too -- can tell you all about their belief in the "Home Run Derby Jinx." It refers to a player's participation in the midsummer event wrecking his swing, causing a noticeable decline in his future numbers.
However, for every Abreu example, there's one like Ryan Howard. Instead of declining statistically after being crowned 2006 Derby champion, Howard actually improved, belting 30 of his 58 home runs after the All-Star break and managing an unreal 1.260 OPS. In fact, he'd homer in three of his first four games after his Derby win, his swing showing no signs of decline.
Those contrasting examples, as well as my tendency to never take such theories -- or perhaps myths in this case? -- as gospel, led me to research whether there is any statistical data to back up "The Jinx." In doing that, I collected the numbers of every participant in the Home Run Derby since its inception in 1985, breaking the stats down into three categories: Statistics accrued from All-Star break to All-Star break the year leading up to the player's appearance ("year before"), statistics accrued from All-Star break to All-Star break the next season ("year after"), and statistics accrued in the player's first 50 games played after his appearance ("50 G after").