A common way to rank things is based on a straightforward metric. For example, football teams are ranked on their total, offensive and defensive performance. Consider the Tampa Bay Buccaneers; they are currently ranked 1st in the NFL in terms of being the stingiest defense based on the yards allowed per game - a measly 47 yards per game or about 2 feet per minute played.
Are they that good or is that the result of something else?
In contrast, when viewed in terms of pass defense they rank dead last giving up more yards per game than any other team. This ranking in turn comes from two contributing factors: the opposition completes both longer plays and a higher percentage of attempts. The result is 353 yards given up by passing.
So, could it be that they are ranked so well in terms of rush defense simply because other teams know they can be successful passing the ball? It turns out that opponents run the ball 32% of the time (5th lowest). So, yes the numbers are skewed based on the distribution of the events themselves. They have good run defense metrics in part because teams don't run the ball.
We tend to like simple numbers, but they can be hiding something important or possibly misleading. Consider typical marketing metrics:
- Conversion rate
- Response rate
- Market share
The trick to communicating insights is to find the right way to present the information; and that usually comes in story book form.
And by the way, Tampa Bay does give up the fewest yards per attempt in the league so they may be that good.
UPDATE: Stats found here http://www.teamrankings.com/nfl/