How do MLB home run derby participants fare after the All-Star break?

There's a popular theory around baseball that participating in MLB's home run derby messes up a hitter's swing. After practicing too many home run cuts, a hitter then loses his normal swing and morphs into a player only going for the long ball.

I decided to test this theory by analyzing the data from the past decade of all home run derby performers.

Before the home run derby, the 80 hitters batted .297 with home runs in every 15.71 at-bats. Following the All-Star break, the same group of sluggers hit .290 with home runs every 18.74 at-bats.

Prince Fielder is a regular in the home run derby. He has two

wins in five appearances. -- Justin Janssen/UT San Diego

In the first half, 71 percent of derby participants hit home runs at a better rate per at-bat and 61 percent hit for a higher batting average than in the second half of the season.

While those figures are quite overwhelming, there's other factors to consider before reaching the conclusion that the derby causes home runs to drop, such as luck/career-year factors or opponents better game planning.

It generally takes a player who has hit a lot of home runs in the first half to be invited into the home run derby. This sampling bias leaves the possibility of second half funks while almost always taking players with a good first half.

To illustrate this bias, only Ivan Rodriguez (2005) belted fewer than 12 home runs in the first half prior to entering the derby, while 37/80 players (granted in roughly 20 fewer games per team) failed to reach 12 in the second half.

Perhaps some of these player invited are having a career season - or at least a career first half. These players pop up every year and are sometimes rewarded with trips to the All-Star Game or home run derby.

In this year's competition, the Reds' Todd Frazier and the Twins' Brian Dozier are having their best seasons of their young careers. The Orioles' Chris Davis would have been in Roger Maris territory if he maintained his 37 first-half home runs.

While the home run rate from the 10 participants in this year's derby is likely to drop in the second half of the season, it's still anyone's guess as to whether the home run derby causes it.

Update: 9:55 p.m.

I went back from the past decade and found the players who entered the All-Star break in the top 10 in the majors in home runs (breaking ties by fewest at-bats needed for home run total).

What I found was that 75 of the 100 hitters -- 34 of which were in the home run derby -- did not maintain their rate of home runs from the first half following the break. 76.5% of the derby entrants and 74.2% of those not participating had lower home run outputs in the second half.