Saw some discussions in a few different threads here on how to determine what a #1, #2, #3, #4, or #5 starting pitcher looks like. I've came up with a method to attempt to define what each of these may look like. Below is the method I used and the data for the 2006 season. Hope you find this as interesting as I did.

I first extracted all starting pitching statistics. I then sorted the data for all pitchers in each league by ERA (Then later XERA). Then, for each league, beginning at the top of the list, I totalled up enough IP to account for a #1 SP for each team in the league. I totalled the statistics for these pitchers and divided by the number of teams in the league to come up with the average #1 SP for the league. I then repeated this process with the remaining pitchers for each of the remaining pitching rotation slots #2 - #5. I determined the number of innings pitched for each rotation slot, by trying to come as close to the following as I could.

Slot IP
#1 220
#2 210
#3 200
#4 190
#5 The Rest

Here is the data for the 2006 season.

2006 ERA Rotation Slots

AL Rot Slots W L ERA GS IP H R ER HR BB SO WHIP XERA
Avg AL #1 SP 17 10 3.41 35 222 209 93 84 22 63 167 1.23 3.59
Avg AL #2 SP 14 11 4.24 34 209 219 107 98 25 62 145 1.35 4.38
Avg AL #3 SP 13 11 4.65 33 199 212 110 103 24 67 142 1.40 4.52
Avg AL #4 SP 11 13 5.23 34 190 217 120 111 29 66 112 1.49 5.26
Avg AL #5 SP 6 14 6.95 29 145 198 120 112 27 58 83 1.76 6.81
Avg AL SP 12 12 4.73 32 189 206 107 99 25 62 127 1.42 4.76

Rotation Slots ERA Range
AL #1 Starters Under 3.87
AL #2 Starters 3.87 - 4.44
AL #3 Starters 4.45 - 4.87
AL #4 Starters 4.88 - 5.86
AL #5 Starters Over 5.86

NL Rot Slots W L ERA GS IP H R ER HR BB SO WHIP XERA
Avg NL #1 SP 15 9 3.31 35 221 200 89 81 21 71 169 1.22 3.46
Avg NL #2 SP 13 12 4.07 34 209 207 104 95 24 66 161 1.30 4.05
Avg NL #3 SP 12 12 4.70 35 202 214 115 106 25 76 141 1.43 4.64
Avg NL #4 SP 10 13 5.34 34 186 211 120 111 27 70 113 1.50 5.19
Avg NL #5 SP 5 11 7.28 21 105 135 90 85 21 48 69 1.74 6.63
Avg NL SP 11 12 4.65 32 188 197 106 97 24 67 133 1.41 4.58

Rotation Slots ERA Range
NL #1 Starters Under 3.79
NL #2 Starters 3.79 - 4.31
NL #3 Starters 4.32 - 4.91
NL #4 Starters 4.92 - 6.00
NL #5 Starters Over 6.00

2006 XERA Rotation Slots

AL Rot Slots W L ERA GS IP H R ER HR BB SO WHIP XERA
Avg AL #1 SP 17 9 3.56 36 225 208 98 89 21 64 177 1.21 3.44
Avg AL #2 SP 15 12 4.38 34 211 211 110 103 26 69 165 1.33 4.17
Avg AL #3 SP 13 12 4.56 34 200 217 110 102 26 65 127 1.41 4.67
Avg AL #4 SP 11 13 5.21 34 192 230 120 111 29 63 106 1.52 5.49
Avg AL #5 SP 6 13 6.82 28 136 189 111 103 26 55 73 1.79 7.03
Avg AL SP 12 12 4.73 32 189 206 107 99 25 62 127 1.42 4.76

Rotation Slots XERA Range
AL #1 Starters Under 3.94
AL #2 Starters 3.94 - 4.39
AL #3 Starters 4.40 - 5.01
AL #4 Starters 5.02 - 5.94
AL #5 Starters Over 5.94

NL Rot Slots W L ERA GS IP H R ER HR BB SO WHIP XERA
Avg NL #1 SP 14 10 3.49 35 222 195 93 86 21 70 184 1.19 3.28
Avg NL #2 SP 13 12 4.08 34 210 206 104 95 25 67 158 1.30 4.05
Avg NL #3 SP 11 12 4.68 33 196 212 111 102 23 68 119 1.44 4.67
Avg NL #4 SP 11 13 5.25 34 188 211 119 109 28 74 121 1.52 5.23
Avg NL #5 SP 5 11 7.03 22 109 143 91 85 22 51 71 1.78 6.81
Avg NL SP 11 12 4.65 32 188 197 106 97 24 67 133 1.41 4.58

Rotation Slots XERA Range
NL #1 Starters Under 3.68
NL #2 Starters 3.68 - 4.37
NL #3 Starters 4.38 - 4.95
NL #4 Starters 4.96 - 5.61
NL #5 Starters Over 5.61

Here is how each of the Reds starters from last season fared.

Reds SP ERA

NL #1 SP ERA GS IP H R ER HR BB SO WHIP XERA
M Belisle 0.93 2 9.7 8 1 1 0 7 4 1.55 3.30
B Arroyo 3.29 35 240.7 222 98 88 31 64 184 1.19 3.69
S Kim 3.60 1 5.0 4 2 2 1 0 3 0.80 3.01
A Harang 3.78 35 233.3 240 109 98 28 56 215 1.27 4.09

NL #4 SP ERA GS IP H R ER HR BB SO WHIP XERA
E Milton 5.19 26 152.7 163 94 88 29 42 90 1.34 5.00
E Ramirez 5.26 19 102.7 120 68 60 13 27 69 1.43 4.95

NL #5 SP ERA GS IP H R ER HR BB SO WHIP XERA
C Michalak 6.15 6 26.3 37 20 18 5 13 8 1.90 7.33
B Claussen 6.19 14 77.0 93 56 53 14 28 57 1.57 5.87
J Germano 6.35 1 5.7 8 4 4 1 2 8 1.77 6.80
K Lohse 6.19 19 100.3 123 70 69 13 38 74 1.60 5.56
D Williams 6.62 13 68.0 92 52 50 14 20 32 1.65 6.67
J Mays 9.89 10 43.7 71 54 48 11 26 21 2.22 9.23

Reds SP XERA

NL #1 SP ERA GS IP H R ER HR BB SO WHIP XERA
S Kim 3.60 1 5.0 4 2 2 1 0 3 0.80 3.01
M Belisle 0.93 2 9.7 8 1 1 0 7 4 1.55 3.30

NL #2 SP ERA GS IP H R ER HR BB SO WHIP XERA
B Arroyo 3.29 35 240.7 222 98 88 31 64 184 1.19 3.69
A Harang 3.78 35 233.3 240 109 98 28 56 215 1.27 4.09

NL #3 SP ERA GS IP H R ER HR BB SO WHIP XERA
E Ramirez 5.26 19 102.7 120 68 60 13 27 69 1.43 4.95

NL #4 SP ERA GS IP H R ER HR BB SO WHIP XERA
E Milton 5.19 26 152.7 163 94 88 29 42 90 1.34 5.00
K Lohse 6.19 19 100.3 123 70 69 13 38 74 1.60 5.56

NL #5 SP ERA GS IP H R ER HR BB SO WHIP XERA
B Claussen 6.19 14 77.0 93 56 53 14 28 57 1.57 5.87
D Williams 6.62 13 68.0 92 52 50 14 20 32 1.65 6.67
J Germano 6.35 1 5.7 8 4 4 1 2 8 1.77 6.80
C Michalak 6.15 6 26.3 37 20 18 5 13 8 1.90 7.33
J Mays 9.89 10 43.7 71 54 48 11 26 21 2.22 9.23