This issue came up recently on the SABR list. One of the issues was why were pitchers from his era who seem to have been about as good he was not in. Then someone else mentioned that maybe the Veterans committee put him because he is a Senator. I posted some evidence on this. Basically it was references to research I had done in the past and seeing where Bunning ranked. I will put that post below, but first something new, although it is a simple, rough estimate of his value (I used Fielding Independent Pitching ERA or FIP ERA to find an imputed winning percentage for Bunning which is fairly high-it's all based on how good he was at strikeouts, walks and HRs). I find that there is some evidence for him being in the Hall, but I don't think it is all on his side. He had a great strikeout-to-walk ratio, which is one indicator of how good a pitcher is.
Below are the top 25 pitchers with 3000+ IP in strikeout-to-walk ratio relative to the league average. Bunning is 19th, which is very good. Mathewson is 1st. He had a strikeout-to-walk ratio of 2.96 while the league average was 1.29. Since 2.96/1.29 = 2.30, Mathewson gets a 230. Data came from the Lee Sinins Complete Baseball Encyclopedia.
I calculated his Fielding Independent Pitching ERA or FIP ERA. The idea is that a pitcher controls HRs, BBs and Ks and hits on balls in play not so much (if you have not heard of this, google Voros McCracken).
Here are the key calculations. HRs, BBs and Ks are per 9 IP.
(1) FIP ERA = Constant + 1.44*HR + .33*BB - .22*K
(2) The constant = League ERA - (1.44*HR + .33*BB - .22*K)
I used Bunning's stats and adjusted them to the AL stats of 2008. Bunning's Ks per 9 IP was 6.83 or about 25% above average. In the 2008 AL K/9IP = 6.36. Raising that 25%leaves 7.97. He walked 2.39 batters per 9 IP or about 26% fewer than average. In the 2008 AL BB/9IP = 3.32. Lowering that 26% leaves 2.47. So those numbers will get plugged into equation (1). The league ERA in the AL in 2008 was 4.35 and the constant for equation (1) works out to 3.21.
We still need to calculate his HRs per 9 IP. He actually gave up 372 HRs while the average was 346. So it looks like Bunning did poorly here. But he pitched in Tiger Stadium for part of his career where an above average number of HRs were hit. So I adjusted his HRs allowed in each season based on the HR park factors from the STATS, INC. All-Time Baseball Sourcebook. For example, if Tiger stadium gave up 20% more HRs than average in a season, I reduced his HRs for that year by 10% (only half of the 20% since he only pitched half his games there). In some of his years with the Phillies, the park factor was below average. After doing this for each of his seasons, his HR total came out to 349, or almost exactly average.
In the AL in 2008, there was just about 1 HR per 9 IP. So I used that for equation (1). With the HR, BB and K data done, I found a FIP ERA of 3.73 for Bunning (adjusted for the 2008 AL).
I then calculated what Bill James calls the Pythagorean winning percentage for Bunning if he pitched on an average team. It is
(runs scored squared)/(((runs scored squared) + (runs allowed squared))
For Bunning, adjusted to the 2008 AL, we get
4.35*4.35/(4.35*4.35 + 3.73*3.73) = .577
So Bunning pitching for an average team would have a .577 winning pct. For pitchers with 3000+ IP, he would be tied for 42nd (with Jack Morris). But I did not calculate the FIP ERA or Pythagorean winning percentage for anyone else. I am just assuming if I did it for everyone, just as many guys would move ahead of Bunning as would fall behind. 42nd is pretty good and seems high enough for a starter to make the Hall.
Now for the post to the SABR list.
I found the best fielding independent ERAs since 1920 (an imputed ERA based on walks, strikeouts and HRs with HRs being adjusted for park effects). Bunning ranked 13th among pitchers with 3000+ IP.
I found that he was 51st in Park-Adjusted Pitching Wins Above Replacement Level.
It also looks like he out pitched Koufax in neutral parks while they were both in the NL.
But he only had 257 Win Shares through 2001, tied for 291st. Not sure where that ranked among pitchers.
He ranks 67th in adjusted pitching wins in Pete Palmer's baseball encyclopedia.