I think you've missed the point of the question durham, the average tenure of a football league manager across the top 4 division in England.

A quick internet search shows that for the season 2014/15 it was 1.23 years.

Notts average since the millennium will probably be half that of not even less. Therein lies the issue (well one of the big issues at Meadow Lane since 2000). It just doesn't work