Last Year the former planning minister paraded statistics that outbuilding is 10% higher in areas with neighbourhood plans than areas with local plans alone.
Quite how this was worked out I dont know since house-building figures are not disaggregated to parish area. I suspect it was simply measured by LPA for those areas with and without any neighbourhood plans. A very crude approach.
This would have meant a sample of areas without local plans being biased to northern areas with less development activity because Respublica data shows neighbourhood plan coverage is weighted towards more prosperous areas.
So Neighborhood plan coverage may not be the causal variable, we may have a classic case of spatial autocorrleation where local priority is the causal variable and neighborhood plan coverage is correlated to that. Indeed there may be a second autocorrelation as when a local plan is adopted housebuilding levels increase and then the neighborhood plan has to be consistent.
Turley in 2014 found half of neighbourhood plans were designed to resist development, so the real correlation may be negative in areas with out of date local plans and positive but non causal in areas with up to date local plans.
If people think that neighborhood plans are there to boost house-building then why isn’t Herefordshire with more than anywhere undergoing a development boom? The main motive is rather to fill a vacuum and restrict development to levels the local community think appropriate.