DVOA ratings represent value from the point of view of the defense, not fantasy football players, and include items that have no impact on fantasy football (such as how many interceptions are caught on passes intended to certain receivers). DVOA of defense against receivers does not include sacks or passes with no intended receiver listed. Passes per game and yards per game are more useful for fantasy football players. These numbers are adjusted based on the opposing offenses and include defensive pass interference.
Note that our decision of which receiver is "number one" and which receiver is "number two" is somewhat subjective. Teams are ranked in order of general passing defense DVOA.