How Reliable are Won-Lost Records, Part III

September 14, 2022

 

 

How Reliable are Won-Lost Records?

 Part III 

 

            In one start, it is nearly impossible for a pitcher’s True Winning Percentage to match his record-book Winning Percentage.  After one start, a starting pitcher’s winning percentage is either .000 or 1.000 (following the tradition of listing a pitcher who is 0-0 as having a .000 winning percentage.)  A pitcher’s one-game winning percentage cannot exceed .950 since, no matter how well the starting pitcher pitches, the other team may also pitch a shutout until the game wanders beyond the control of the strongest starting pitcher.  If a pitcher pitches well, then, there is at least a 50-point (.050) margin between his winning percentage and his true winning percentage. It IS possible for a starting pitcher to pitch so badly that his team’s chance of winning is near zero; possible, but not common. 

            There are 4,877 pitchers in my data who made at least one major league start, of whom only 3 pitched so badly that their True Winning Percentage after one start was within 10 points (.010) of zero.  That is one in 1600, which will show in the charts later as 0%. 

            After two starts, a pitcher’s record-book winning percentage has three possible landing spots:  1.000, .500, and .000.  After three starts, there are five possible landing spots (1.000, .667, .500, .333 and .000.   .500 is possible, and common, because most pitchers do not have three decisions after three career starts.)

            As the number of possible winning percentages increases, the number of pitchers who have about the same True Winning Percentage as record-book Winning Percentage increases.   After one start, the average gap between Winning Percentage and True Winning percentage is 369 points (.369).  After two starts it drops to 327 points; after three starts, to 272 points.  After four starts, the average gap between a pitchers winning percentage and his true winning percentage is down to .229; after five starts, down to .198. 

            After one start, zero percent of starting pitchers have winning percentages within 10 points of their true winning percentage.  After two starts, it is 1%; after three starts, 2%, and four starts, 3%, and after five starts, a higher 3%. 

            Winning percentages within 100 points True Winning Percentage are, of course, more common.   After one start, 5% of pitchers have winning percentages within 100 points of their True Winning Percentage; after two starts, 13% do, after three starts, 23%, after four starts, 29%, and after five starts, 33%.  After 438 starts, 100% of pitchers have winning percentages within 100 points of their True Winning Percentage. 

            Does True Winning Percentage predict a pitcher’s future Winning Percentage better than Wins and Losses predict themselves?  I would be shocked if the answer is "No", but I did not actually study that question.  It would seem to me intuitively that the convergence of True Winning Percentage and record book winning percentage as starts increase is nearly proof that True Winning Percentage is the dominant hand, but it just didn’t occur to me to actually study that while I was doing the work. 

            Anyway, this chart states the facts I have already given you (and more).  I’ll highlight the numbers I have already given you; I am just trying to teach you to read the chart:

 

Starts

Discrepancy Average

10

20

30

40

50

60

70

80

90

100

1

.369

0%

0%

0%

0%

1%

1%

2%

3%

4%

5%

2

.327

1%

3%

4%

5%

7%

8%

9%

10%

12%

13%

3

.272

2%

5%

7%

10%

12%

14%

16%

19%

21%

23%

4

.229

3%

6%

9%

12%

15%

17%

20%

23%

26%

29%

5

.198

3%

7%

11%

14%

17%

20%

23%

26%

29%

33%

6

.180

4%

8%

11%

15%

18%

22%

25%

29%

33%

35%

7

.162

4%

8%

12%

16%

20%

23%

28%

31%

35%

38%

8

.149

4%

8%

12%

17%

21%

25%

29%

33%

37%

41%

9

.141

5%

9%

14%

18%

22%

26%

30%

34%

39%

42%

10

.133

5%

9%

14%

20%

24%

29%

33%

37%

41%

44%

 

            After ten starts the average margin between Winning Percentage and True Winning Percentage is 133 points, and 44% of pitchers are within 100 points of their True Winning Percentage.   

            This chart below extends the one above out to 450 starts.   There are 57 pitchers in my data who made 450 or more major league starts.  Above 450 starts, we don’t have enough data for the percentages to be meaningful.   We start to lose accuracy at about 300 starts.  There were 237 pitchers in the data who made 300 or more starts, and the data holds together fairly well up to 300 starts, but we start to lose consistency in the data above 300 starts, and the sample size of pitchers gets smaller.

 

Starts

Discrepancy Average

10

20

30

40

50

60

70

80

90

100

1

.369

0%

0%

0%

0%

1%

1%

2%

3%

4%

5%

10

.133

5%

9%

14%

20%

24%

29%

33%

37%

41%

44%

20

.095

7%

15%

21%

28%

34%

39%

45%

49%

55%

60%

30

.080

9%

17%

24%

31%

39%

45%

52%

57%

62%

68%

40

.073

9%

17%

25%

34%

41%

49%

56%

62%

68%

73%

50

.064

11%

22%

30%

39%

47%

55%

62%

68%

74%

79%

75

.056

13%

23%

33%

43%

52%

61%

68%

75%

81%

86%

100

.048

14%

27%

41%

51%

60%

68%

75%

82%

87%

90%

150

.041

18%

32%

46%

58%

68%

77%

82%

87%

92%

94%

200

.037

17%

37%

50%

64%

73%

80%

86%

89%

93%

97%

250

.035

19%

37%

52%

67%

74%

83%

88%

92%

95%

98%

300

.032

22%

38%

57%

70%

80%

87%

92%

96%

97%

99%

350

.032

21%

42%

55%

68%

79%

86%

93%

97%

99%

99%

400

.031

24%

38%

56%

74%

82%

89%

90%

95%

98%

99%

450

.034

18%

30%

54%

63%

82%

86%

89%

96%

100%

100%

 

            And this chart extends the chart above sideways to 250 points (meaning a discrepancy of .250 or less between Winning Percentage and True Winning Percentage.)

 

Starts

110

120

130

140

150

200

250

1

6%

8%

9%

10%

12%

21%

28%

10

48%

52%

55%

59%

63%

77%

85%

20

64%

69%

72%

76%

79%

91%

95%

30

72%

76%

81%

84%

87%

96%

98%

40

77%

81%

85%

88%

91%

98%

99%

50

83%

86%

89%

91%

94%

99%

100%

75

89%

92%

94%

96%

97%

100%

100%

100

93%

95%

97%

97%

99%

100%

100%

150

96%

97%

99%

99%

100%

100%

100%

200

98%

99%

99%

99%

100%

100%

100%

250

99%

99%

99%

100%

100%

100%

100%

300

99%

99%

99%

100%

100%

100%

100%

350

99%

99%

99%

99%

100%

100%

100%

400

99%

99%

99%

99%

100%

100%

100%

450

100%

100%

100%

100%

100%

100%

100%

 

            By 50 starts, all pitchers have winning percentages within 250 points of their True Winning Percentage, but that is a very wide net.  That just means that if a pitcher has a Winning Percentage of .600 after 50 starts, that his True Winning Percentage had been somewhere between .350 and .850. 

            So how do we generalize about this, in the English Language?   It’s arbitrary, but let me suggest this.  If the average gap between Winning Percentage and True Winning Percentage was .000, then Won-Lost records could be said to be 100% reliable.  For each .001 of separation between them, we could say that that is a 1% drop in reliability. 

            If you agree to that definition, then won-lost records are completely uninformative (100% unreliable) through 17 starts. 

            Through 35 starts, which we could say is one season, won-lost records are 24% reliable, 76% distorted by events beyond the pitcher’s control. 

            Through 100 career starts, we could say that won-lost records are 52% reliable, 48% distorted.   The point at which the 50% mark is crossed is 93 starts. 

            Through 200 career starts, won-lost records could be said to be 63% reliable. 

            Through 300 career starts, which we could say is a full career, won-lost records could be said to be 68% reliable. 

            Although the reliability would continue to increase above 300 starts, the data samples are too small to draw any conclusions.  It is apparent, however, that for won-lost records to become 90% reliable as a reflection of how well the pitcher has pitched would take much, much, much longer than any pitcher’s career.  80%, you can argue

            In the fourth article of this series, posted tomorrow, we’ll talk about individual pitchers—the pitchers with the highest True Winning Percentages, the pitchers whose record-book winning percentages are most inflated, the pitchers who were better or worse than their won-lost record shows, etc. 

 

 
 

COMMENTS (4 Comments, most recent shown first)

raincheck
shthr wrote:

“Who was that one pitcher back in 1600?

Cotton Mather?

Was he a Yankee? “

Funny. I read the same way, and had to reread it to get the actual meaning.
4:34 PM Sep 16th
 
shthar
Who was that one pitcher back in 1600?

Cotton Mather?

Was he a Yankee?


3:22 AM Sep 16th
 
shinsplint
Since the True Winning Percentage (TWP) includes no-decisions games, unlike Winning Percentage (WP), it's interesting that those games don't cause a larger discrepancy between TWP and WP. That suggests that a pitcher's Game Score for no-decision games must have a high correlation with an average Game Score for that pitcher.

In regards to what is a better predictor of the future, I think that it depends on the level of offense of his team. If it's an average offense, and the pitcher is getting bad run support, for example, the TWP is a better indicator of how well he will do in the future since his luck will likely even out.

But if the pitcher is on a team with bad offense, for example, he's likely to continue to have a lower WP than TWP for his entire career. Same thing for a player with good offense. He'll likely have a higher WP than TWP for his career. So in these cases his current WP is probably a better predictor of his future WP.

The convergence of WP and TWP as starts accumulate must be mostly the effect of the evening out of luck for pitchers who pitch for teams that don't have roughly average offenses.
3:21 PM Sep 15th
 
mpiafsky
May we know those terrible 3 starts?
I assume the data doesn't go back that far but Allan Travers in the bizarre Cobb suspension game of 1912 probably has a 0, right?
1:02 PM Sep 15th
 
 
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