One of the major lessons of the behavioural economics program is that our judgment is very much context or domain specific and that we have a tendency to compare choices relatively rather than absolutely.
I think this lesson is important to consider when comparing the effectiveness of managers across all sports. Manchester United, of course, is the obvious example. David Moyes reign is compared to his predecessor and his effectiveness is being judged from performance of the club under Alex Fergusons guidance.
While not doubting that football has changed an awful lot over the years, the tables below allow Manchester United fans to compare their manager’s successfulness absolutely. These tables show the win percentage of Manchester United mangers through time and then ranks them (the data is taken from Wiki…so perhaps take them with a pinch of salt). Also keep in mind that some managers were at the helm for different time periods (hence why David Moyes comes 2nd in the ranking in the second table).