After learning of his firing on Tuesday, former Dallas Cowboys defensive coordinator Rob Ryan told ESPNDallas.com's Tim MacMahon the following:

"I inherited a team that was 31st in the league in defense and made them better. I (expletive) made them a hell of a lot better. I'll be out of work for like five minutes."

Given Ryan’s extreme amount of confidence and propensity to speak his mind, this type of statement comes as no surprise. But is it actually true?

A quick look at the numbers from 2010 -- the year before Ryan was hired by the Cowboys -- shows that Ryan was referring to points allowed per game (often referred to as “scoring defense”), as the Cowboys ranked second-to-last in the league with 27.3 Opp PPG that season.

Looking at the same number for the past two seasons with Ryan calling the defense, the Cowboys ranked 16th in the league with 21.7 Opp. PPG in 2011 and 24th with 25.0 Opp. PPG in 2012. While most wouldn’t interpret those numbers as befitting of a “top” defense, they would seem to indicate some improvement from 2010 when taken at face value.

But a major issue here is with how defense is being measured. Is scoring defense really a true measure of defense and defense only? Examining more in depth, there are a few reasons why that statistic could be misleading:

While most points are allowed by the defense, points can be scored on return touchdowns against the offense or special teams but still count towards a defense’s “points allowed.”

On the flip side, defenses can score touchdowns, which improves their teams’ “scoring offense” but doesn’t directly show up in scoring defense.

Defenses that have to face shorter fields as a result of poor offenses or special teams are likely to give up more points. This can result in them in having a higher Opp. PPG due to poor performance by other units on their teams, not the defense itself.