In 2002, Rich Gannon, a former 4th round pick, led the NFL in passing yards. That year, Tom Brady (6th round), Trent Green (8th round), Aaron Brooks (4th round), and Jeff Garcia (undrafted) were in the top 11 in passing yards, while Jon Kitna (undrafted), Matt Hasselbeck (6th), and Brad Johnson (9th) all gained at least 3,000 passing yards, too. You can find all that information here. So in a year where only 17 quarterbacks threw for 3,000 yards, nearly half of them were drafted in the 4th round or later.

Ten years later, the quarterback landscape was very different. Other than Tony Romo, Brady, and Matt Schaub, all of the top 17 leaders in passing yards were drafted inside the top 35. Last year, Brady, Romo, and Russell Wilson were the only quarterbacks in the top 20 in passing yards not taken inside the first 36 picks (#36 was the draft slot for both Bay area quarterbacks, Colin Kaepernick and Derek Carr).

But those are just three isolated years. How does the trend look over time? Here’s what I did.

1) Convert each player’s draft pick selection to its draft value.

2) For each player with passing yards in a season since 1970, calculate their percentage of league-wide total passing yards.

3) Multiply that number by each player’s draft value. Then sum those values to get a weighted-average of the draft value for each quarterback.

Here are the results: the number on the Y-Axis may not mean much to you in the abstract (it’s the weighted average draft value), but it’s the shape of the curve that’s important.

As a general rule, the modern passing attack barely resembles what was going on in the early ’70s, but there is at least one exception: an emphasis on quarterbacks that were highly drafted. For example, an overwhelming number of early draft picks are at the top of the passing charts from 1972. That trend didn’t hold for very long, though. Then, in the early ’90s, things peaked again for highly drafted quarterback. In 1994, five of the top seven passers were former top 3 picks, with the other two going in the top 33 selections.

My hunch is that this trend is going to stick around this time: once Brady and Romo retire, there may not be much out there other than Wilson (and perhaps Nick Foles) when it comes to quarterbacks drafted outside of the top 40. This year, Buffalo, Houston, and Cleveland may be going with quarterbacks that were not highly drafted, but those appear to be short-term solutions, anyway. And, at least for 2015, we have four top-2 picks that should boost the average. Carson Palmer should be back in Arizona after starting just 6 games last year, while Sam Bradford is a projected starter after missing all of 2014. And we should also see Jameis Winston and Marcus Mariota helping to bring up last year’s average.