That's a really interesting study daphnedill.
Amazing that the "surgeons" (studied PE/RE) get the most accolades and honours, as well as the highest salaries, yet appear to be the least effective heads. As many educationalists have suspected, low performing children are "weeded out" of these schools, thus elevating exam results - and it was found that the improvement could not be sustained when the heads left.
How interesting that the "architects" (studied History/Economics - 86% had worked outside of education before becoming teachers) who place great emphasis on visionary leadership which encourages the involvement of the community and which involves re-designing and transforming schools, achieve gradual but sustained improvement which continues after they leave.
A bit worrying that the bulk of the heads, the "philosophers" (studied English/Languages)are characterised as being good at "talking the talk" but not "walking the walk" and were recorded as presiding over a "gradual decline" in the schools.
This certainly does seem to support the idea that an effective head of any organisation is instrumental in creating the conditions that enable an organisation to achieve sustained improvement.