Before the Ravens won the Super Bowl, much was said that their defense could not be considered as being among the best in history unless they won the Super Bowl. And we excluded the strike years of 1982 and '87. That said, the two defenses that stand out are the 1985 Bears and the 2000 Ravens. The Ravens outrank the Bears in three of these four categories, although in points allowed and yards allowed, the teams are relatively close. Here is a brief explanation of standard deviation and how it applies to football.
Standard deviation is used to measure the dispersion, or difference, in a set of numbers.
Here's an example that might help. Let's look at points scored and points allowed for the 2000 Rams. The Rams scored 540 points and allowed 471. The Bears were better at defending the pass than the Ravens while the Ravens were better against the run. Here's where standard deviation enters the equation.