The other day I was wondering about whether or not teams act rationally when making their shooting decisions, and I have some ideas about how to determine this, but I’ll post on that later. For now, I’d like to present a something really interesting I discovered as I was going through the data.
First of all, over the Modern era (1979-80 through today), points per three-point attempt have almost exactly equaled points per two-point attempt, at approximately 0.973 (which is, interestingly, almost exactly one point per fga). This lead me to believe, at first, that it would be a good measure of shooting-decision rationality to compare a team’s or a player’s points-per-shot from inside and outside the arc: if pts/3fga, for example, is substantially higher than pts/2fga, it would seem to indicate that too many bad two-pointers are being attempted, and that some of those should be passed out for three-point attempts (but more on this in another post).
What I found in doing a little EDA, however, indicated that if this is how we conceive of rationality, the league as a whole has not been rational on a year-by-year basis (which sort of undermines my claim). What I did find, instead, was that pts/3fga are now higher than pts/2fga, leaguewide. However, this has not always been the case:
It appears as though when the three-pointer was first introduced (the season which I mark as the beginning of the “modern” era) defenses were at first unprepared to handle it, but then the quickly adapted, and the ratio of pp3/pp2 was fairly low for a while. However, from the mid-80s onward, that ratio steadily increased, until today, when the league seems to have achieved some sort of equilibrium at which pp3 is noticeably greater than pp2. Not being a basketball historian, this is just the best explanation I have come up with, and I would be very interested in hearing someone more knowledgeable give me a better story to go with the data.