The rise of the three-pointer

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:

Adoption of the three-pointer

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.

2 responses to “The rise of the three-pointer

  1. Interesting stuff. The fact that more fouls are drawn on 2-point attempts might be one explanation for the uneven equilibrium.

    Have you considered investigating whether there is (or has been) a correlation between 3 pointers attempted and offensive efficiency?

  2. Very interesting analysis. I knew the number of three point attempts has been steadily rising since it was introduced, but I was unaware that the efficiency of the shot had also been rising (although it has leveled off recently).

    One explanation for the early inefficiency of the 3pt shot would be that before 1979, there was no such thing as a three point shooter (except for those who had played in the ABA prior to the NBA). Most players at the time had gone their whole career without shooting three pointers, so it would make sense that they wouldn’t be so good at it at first. But as new players entered the league (and as the NCAA added the three) guys started to become more comfortable with the shot and it became a more important part of the game. By the time the mid-90’s hit, players had been playing (and practicing) the three for the majority of the basketball-playing lives.

    I’m no historian myself, but that’s my two cents.

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