Sunday, July 27, 2014

Factors That Might Determine A Batter's GIDP Rate

I looked at how some variables impact GIDP rate using regression analysis. All data is from Baseball Reference. The variables were

Lefty-A dummy variable for being a lefty (1). Righties got 0. Switch hitters got .67, assuming they face righties about 2/3 of the time

SO%-Strikeouts divided by PA - IBB. Players who strikeout alot probably won't hit into too many DPs

IsoCon-Isolated power on contact. So extra bases divided by AB - SO. I wondered if how hard you hit the ball mattered. Maybe the harder you hit it, the easier it is to turn a DP. But maybe hard hit balls go through more or a line drives or long flies.

Speed-Triples divided by 2B + 3B. This is an idea from Voros McCracken. Fast guys turn those balls hit into the gap into 3Bs, slow guys get 2Bs.

GB/FB ratio-not used in the first regression

I looked at all AL batters who had 800+ PAs combined in 2012-3. Here is the first regression equation:

(1) DP Rate = .185 - .029*Lefty - .178*SO% - .031*IsoCon - .168*Speed

 Here are the t-values for each variable

Lefty) -4.49
SO%) -2.45
IsoCon) -1.04
Speed) -3.03

The r-squared was .393 and the standard error was .029. The mean for all the players in the group (93) was .1122.

I wanted to see how much conventional stats could explain the rate first. Then I added in GB/FB ratio. Here is the second regression equation

(2) DP Rate = .075 - .025*Lefty - .15*SO% + .071*IsoCon - .191*Speed + .096*GB/FB

The r-squared jumped to .599 and the standard error of the regression fell to .024. Here are the t-values

Lefty) -4.61
SO%) -2.51
IsoCon) 1.37
Speed) -4.21
GB/FB) 6.69

So 4 of the variables look significant being greater than 1.96 in absolute value (at the 5% level). Interesting that IsoCon saw a change in sign. The GB/FB ratio sure increased the r-squared alot.

Being a lefty lowers your rate by .025. So if you were otherwise average (.1122), then you fall to .0872. If your strikeout rate goes from .1 to .2, your DP rate falls by .015.

The GB/FB ratio ranged from 1.85 (Jeter) down to .475 (Reddick). A .25 drop in the GB/FB ratio would lower your DP rate by .024. Jeter had the highest DP rate of .245. Kendrick was 2nd with .199. Granderson was lowest with .032

The Speed variable went from .224 (Austin Jackson) down to 0. An increase of .1 here means a drop of .019 in DP rate.

Most of this is not a surprise. It might be worthwhile to add in more years of data. It will also be interesting to see what happens to the sign on the IsoCon variable with more data.

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