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When Do Stats Become Meaningful?
Posted by Troy Patterson on Thursday, April 30, 2009
Sabermetric StatisticsI originally found this data at the site BrockforBroglio.com, which is now gone. After trying a few different searches, I found the data at THT Fantasy Focus, and it is based on work by Pizza Cutter at Statistically Speaking. They posted this in April last year, but it should be reviewed every year.
Here is the article about hitters, and here is the article about pitchers, but below you can see the central point.Hitters
Strikeout rate/Contact rate*: 150 PA
LD%: 150 PA
Walk rate: 200 PA
GB%: 200 PA
GB/FB: 200 PA
FB%: 250 PA
Home run rate: 300 PA
HR/FB: 300 PA
BABIP: Doesn't reach a 0.50 r-squared at 650 or below.
Batting average: Doesn't reach a 0.50 r-squared at 650 or below. Pizza Cutter guesses it would be at around 1000 PA.
Pitchers
K/PA: 150 BF
GB%: 150 BF
LD%: 150 BF
FB%: 200 BF
GB/FB: 200 BF
K/BB: 500 BF
IF FB%: 500 BF
BB/PA: 550 BF
BABIP: Doesn't reach a 0.50 r-squared at 650 or below.
HR/FB: Doesn't reach a 0.50 r-squared at 650 or below.
The moral of the story is that we can't make too many judgements yet. No batter has topped 150 PA, and there are only a few pitchers over 140 BF. This means many of our ratios and stats are not quite ready to be viewed yet. Just because a pitcher has upped his K/9 by 3 he likely has not faced enough hitters yet and it will return to career levels.
As we enter the middle of May, we should be able to get a much better picture of where we stand. Just another reminder to relax in April and wait for more information.
2 comments:
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i Noticed that as well. My guess is even if LD and GB are significant there is still some variance. If you combine their variance that doubles the variability put into FB%.
Just a guess, but that would be my understanding.
So if Pitcher A has reached 22% LD rate and a 45% GB rate he has a resulting 33% FB rate. Perhaps his actual rates should be 20% and 42%, but they are within a standard deviation. This means he should have a 38% FB rate which is outside the standard deviation for FB%.
These are made up numbers, but would be my understanding of why FB% takes more BF.
Not sure I get how LD,and GB% become meaningful after 150 PA but you have to wait until 200 for FB%. If LD% and GB% are claimed to be meaningful after 150 PA then 1-ld%-gb% is meaningful after 150 PA