Converting 40 times to NCAA 10 SPD

[JeffHCross]

Over the weekend I started using a much more thorough list of NFL draft eligible players. Ended up recording the 40 times and SPD ratings of over 1100 players. Some of them may not have been accurately recorded, but that's one reason for the increased sample size ... it should all come out in the wash. And, for the most part, it did.

The Results (for the so inclined)

Spoiler: show

1. I validated my original equation for All Positions. Even with a five-fold increase in players, there was less than 1% difference in the "All Players" equation for the original list and the new list.
2. It's obvious that some positions have limits on SPD ratings. This is a huge impact to trying to determine SPD by position. Because the SPDs had some inaccuracy, this meant that about 45% at certain positions were above the Trend Line, 45% were below it, and very few were actually on it. The Trend Line was nearly flat, even though the SPD range for the position was fairly wide. That would result in very inaccurate results for my Per-Position SPD conversion.
3. Offensive Lineman are horribly slow compared to other positions, in SPD. No Lineman breaks 80 SPD. Very few break 70. Yet the fastest in the draft, Bruce Campbell of Maryland, ran a 4.75 40. Campbell was 55 SPD in NCAA 10. Just to use two examples, Colt McCoy is listed at 4.79 with 80 SPD and T.J. Pitts (Memphis) lists a 4.76 with 89 SPD.
4. Just to emphasize the last point, the "average" for a DT is a 5.13 40 and 65 SPD. The "average" OL is a 5.25 40 and 57 SPD.

The Equations
If anyone's actually reading this, this is probably what you're really interested in.

I decided to take the breakdown one step further this time, and include categories for the different positions. The reason for this is that some positions in NCAA are designed to have limits in max SPD and min SPD. If I'm trying to convert real 40 times to SPD ratings, I have to take this into account. Combining similar positions into categories allows for more accuracy in the conversion while making sure that the conversion for my QB isn't affected by a DL's SPD rating.

Off Backfield = Quarterbacks and all Running Backs
Receivers = Wide Receivers and Tight Ends
Trenches = Offensive and Defensive Linemen
Back 7 = Linebackers and Defensive Backs

	Slope	Y-Int	equation
All Players	-40.23	271.64	SPD = -40.23 * (40-time) + 271.64
QB	-21.67	178.97	SPD = -21.67 * (40-time) + 178.97
HB	-13.39	150.8	SPD = -13.39 * (40-time) + 150.8
WR	-13.42	150.98	SPD = -13.42 * (40-time) + 150.98
TE	-15.16	154.51	SPD = -15.16 * (40-time) + 154.51
OL	-6.15	89.21	SPD = -6.15 * (40-time) + 89.21
DT	-11.79	125.34	SPD = -11.79 * (40-time) + 125.34
DE	-8.85	121.11	SPD = -8.85 * (40-time) + 121.11
LB	-6.03	111.36	SPD = -6.03 * (40-time) + 111.36
CB	-3.43	106.3	SPD = -3.43 * (40-time) + 106.3
S	-8.79	129.26	SPD = -8.79 * (40-time) + 129.26
Off Backfield	-33.76	241.35	SPD = -33.76 * (40-time) + 241.35
Receivers	-24.96	202.7	SPD = -24.96 * (40-time) + 202.7
Trenches	-34.21	239.24	SPD = -15.47 * (40-time) + 140.09
Back 7	-22.62	191.51	SPD = -22.62 * (40-time) + 191.51

And now some examples:

Examples	QB	HB	WR	TE	OL	DT	DE	LB	CB	S		All Players	Off Backs	Receivers	Trenches	Back 7
4.29	86	93	93	89	63	75	83	85	92	92		99	97	96	92	94
4.43	83	91	92	87	62	73	82	85	91	90		93	92	92	88	91
4.56	80	90	90	85	61	72	81	84	91	89		88	87	89	83	88
4.71	77	88	88	83	60	70	79	83	90	88		82	82	85	78	85
4.92	72	85	85	80	59	67	78	82	89	86		74	75	80	71	80
5.03	70	83	83	78	58	66	77	81	89	85		69	72	77	67	78
5.27	65	80	80	75	57	63	74	80	88	83		60	63	71	59	72

(I hope you can tell that the categories produced much better results than the individual positions)

Just while I was writing this up, I've already made a change, but I hope that's my last one. Originally, my categories for defensive players had OLs and DTs in one, DEs and LBs in another, and CBs with Safeties in the final category. This didn't produce satisfactory results, especially for the defensive backfield. By grouping the DEs in with the other lineman, and moving the LBs with the defensive backfield (Back 7), the results were much more satisfying.

For example, originally a 4.29 DB was listed at 92 with a 5.27 DB at 83. 94 and 72, respectively, are much better in comparison to the other ratings.

Hope this is of use to, well, anybody besides me.