The early AFL was unstable, which probably isn’t too surprising. This was most clear in 1963, which must be one of least sticky league seasons in pro sports. The Oakland Raiders, under new coach Al Davis, jumped from 1-13 to 10-4. The San Diego Chargers, who added quarterback Tobin Rote and had a breakout season from second-year wide receiver Lance Alworth, went from 4-10 to 11-3 and league champions.

Meanwhile, three of the eight teams in the AFL had huge declines.

- The Houston Oilers had been the class of the early AFL, winning the title in ’60 and ’61, before falling in the championship game in ’62. But in ’63, Houston dropped from 11-3 to 6-8.

- Houston lost in the ’62 AFL title game to Lamar Hunt’s Dallas Texans, who went 11-3 behind coach Hank Stram and quarterback Len Dawson. But after moving to Kansas City in the off-season, the team went just 5-7-2.

- Denver went 7-7 in 1962, with a pass offense and a pass defense that was both about average. But in ’63, both ranked last in the league, and the Broncos fell to 2-11-1.

The graph below shows each team’s winning percentage in 1962 (on the Y-Axis) and in 1963 (the X-Axis), along with a trend line. In a stable lead, the teams would form a diagonal line that starts on the bottom left and goes up to the bottom right; i.e., as win percentage rises in Year N, it rises it Year N+1. Yet here, the trend line is the exact opposite. That’s because there was a strong negative correlation (-0.49) between winning percentage in the two years.

So yeah, the AFL was really unstable in 1963. This isn’t just a function of it being a small league: by 1969, the AFL was extremely stable, as we’ll see in a minute. The impetus for this experiment? I was curious if the NFL is more or less sticky now than it used to be. In other words, is team performance more volatile or less volatile now than it used to be?

There is no perfect way to measure this, and there are some things I haven’t quite figured out how to handle.^{1} That said, here is what I did:

1) Calculate each team’s winning percentage in Year N, and pro-rate to 16 games to get wins per 16 games in Year N.

2) Calculate each team’s winning percentage in Year N-1, and pro-rate to 16 games to get wins per 16 games in Year N-1.

3) Square the difference, to give more weight to extremes.

4) Sum that result for all teams in that league for that season (Year N season).

5) Take the square root of that result, and then divide by the number of teams.

I have graphed the results below, which shows that the average team changes by about 3-4 wins per year. The AFL is in orange, while the NFL is blue.

In general, there does appear to be more volatility now. That would make it more impressive for some team like the Patriots to keep being dominant year after year than it would be for a team to do so in the ’70s. That’s probably not a *surprising* result, but it’s at least good to have some evidence of it.

- One thing I have been thinking about: If there is more parity now (not sure if that’s accurate), that means teams are closer to .500 to begin with. We know about general regression to the mean, so if there are fewer teams with extreme records, that would negate some natural volatility in team records (for example, if there used to be a ton of 10-2 teams, we know we would project them closer to say, 8-4 the next year; the same goes for an 11-5 team moving back to the pack, but that “move” would look less extreme. [↩]