Thanks for the feedback to Thursday's post on the state of the NFL's passing game and the countermeasures, if any, that defenses might find available. As I anticipated, many of you grabbed the numbers in our monster chart and started looking for explanations.

I received several versions of this question: What has accounted for the rise in passer rating over the past 25 years, considering that yardage and attempts have risen mostly in concert with expansion? After all, as many of you figured out for yourself, yards per attempt hasn't risen much over time.

After looking through some of the information I didn't include in the chart, I think we can quickly point to one factor that leads to a second. Without a doubt, the past 25 years has provided increased efficiency via completion percentage.

Let's discard the 1987 season because it included three "scab" games during the NFL players strike.

In 1988, NFL quarterbacks combined to complete 7,670 of 14,131 passes for a percentage of 54.3 percent.

In 2011, NFL quarterbacks combined to complete 10,465 of 17,411 passes for a percentage of 60.1 percent.

In a 60-pass game, the difference between 60 percent completions in 2011 and 54.3 percent would be three or four completions. That doesn't sound like much, but in terms of passer rating it makes a significant difference. It also adds additional opportunities for touchdowns over the course of a season. Indeed, teams are scoring more now via the air. They're doing it more efficiently as well.

In 1988, NFL teams threw 556 touchdown passes. That's an average of one touchdown per 25.4 attempts.

In 2011, NFL teams threw 745 touchdown passes. That's an average of one for every 23.4 passes.

That's a quick answer to what might prove a bigger issue. I got a number of other really interesting questions that will require more research, and in all likelihood, some help from the statistical analysts at ESPN Stats & Info. More to come on those topics. And, by all means, keep them coming.