I wonder what the average number of complaints is for an officer working the same area?
Depends. A cop who works the schools handing out teddy bears gets very few. Likewise one in a quiet UMC suburb. One who works the worst part of town, and works hard often gets a lot. And the same is true for a low quality cop.
18 complaints means he might be a hard working great cop who is always involved in anything happening out there. Or it could mean he is poor quality slub and poorly supervised.
Numbers tell you very little.