Robust M-T Draft Team Comparisons

Previously, I ranked teams in terms of how well they converted conventional draft points into surplus performance value as calculated by the Massey-Thaler (M-T) study. Teams were ranked by draft points, then ranked by M-T value. The difference between each team's rankings indicates how well each team played the Massey-Thaler game.

Comparing ordinal rankings is not the most sophisticated analysis. Statisically speaking, continuous variables are more robust than ordinal variables for analyzing correlations.

So to see if a team, or teams, stood out at maximizing M-T surplus value, I regressed conventional draft points onto M-T value. In other words, I performed a simple regression with draft points as the independent variable and M-T value as the dependent variable. The sample includes the '02-'06 drafts.

The "residual values" of the regression are the differences between the predicted team M-T values and actual M-T values. If teams did no trading, and made no effort to increase M-T value, then the residuals should be zero, or close to zero. If a team made an effort to maximize M-T value then the residual for that team would be positive. Negative residuals indicate a team has "squandered" value in M-T terms.

Below is the table of residuals. For comparison, the table includes the difference in conventional points ranking and M-T value ranking I previously used to compare teams. Also listed are the team wins for the sample time period '02-'06.

The Titans and Rams are at the top of the list, while the Redskins again are at the bottom. There seems to be a drop-off from Tennessee and St. Louis to the rest of the pack. Perhaps they are teams that have struggled with salary cap issues during the time period, then were forced to makee draft pick trades to minimize the cap hit of their picks.

The average number of wins for the period is 40. The big question is 'how do team wins correlate with M-T value over the same time period?' The correlation coefficient is 0.44 (r-squared = 0.19). About 20% of the variance in wins can be accounted for by Massey-Thaler surplus value.

This is very remarkable. Conventional draft points should correlate very negatively with team wins. The more a team loses, the higher the picks it gets. In fact, the correlation between team wins and conventional draft points is -0.65.

M-T values are not as directly related to a team's previous record as conventional draft points. However, the losing teams with the higher picks still start with more M-T value than the winning teams with later picks. Therefore, if there is no "M-T phenomenon," then we'd expect the correlation between M-T "effort" and wins to be weaker than between conventional draft points and wins, but also decidedly negative.

Instead, we find that the correlation is solidly and significantly postive. (The significance threshold is 0.15.)

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