Feature update: retention tweaks, and a note on average running position

First update: the maximum denominator of the retention score weights is now 20 instead of 10 to better represent the realities of the sport. The top twenty cars are competing for playoff spots. 10 and 20 are equally arbitrary, but 20 has that backing it. The original post has been updated and contains much more information.

Second: One of the flaws of the weighted retention scores was that it didn't give any credit for running up top. If there's a constant battle between second and third, they can rack up a lot of points. Meanwhile the guy in first gets nothing. The new "Position Unchanged" rating assigns 1/(current position +1) points for each lap where a driver's position is unchanged (cautions excluded as always). Net Retention is thus gain rating + unchanged rating - loss rating, and Retention Ratio is (gain + unchanged) / loss.

You can think of these new stats as geometric and weighted versions of average running position (which is arithmetic). Whereas average running position says the difference in importance/ difficulty / etc. between, say, 19th and 20th is the same as that between 2nd and 1st, these weighted metrics say that it's very, very different (an order of magnitude). The weighted metrics represent reality at the pay window and the negotiating table. But the NASCAR standings, which use a linear points system, side with the traditional running position. Which is better in reality? They each have their purposes. You can decide.