JRs and Dodgy Neighbourhood Plan Statistics – Some thoughts

Interesting story in Planning

The High Court has ruled that ministers should have released documents to back up a claim that adopted neighbourhood plans were delivering 10 per cent more housing than those planned for by the relevant local planning authority.

My thoughts

Its probably true- but what does it tell you?

But how do DCLG know as they don’t have completions data by Parish?

To be statistically meaningful you need some kind of matched pairs analysis.  One Parish with an NP match with a similar parish without (double blind matched of course).

And even then you need to test for what is called spatial autocorrelation, and do a kind of VAR test (which distinguishes between correlations and causation), jargon I know but important.

Its important because in areas without 5 year supplies you will expect a lot of development pressure, and greater incentive to do a neighbourhood plan.  Therefore you would expect more neighbourhood plans and potentially more with allocations and completions.  But its essential what you compare against, the same kind of area or same authority with an NP or another areas in another part of the country without development pressure or with an up to date local plan and with a 5 year supply?  Unless you control for these variables you will get meaningless and spurious correlations. The ‘spatial autocorrelations’ where the causal variable is not NP status but things like location.

DCLG in recent years is hardly known for its statistical expertise is it?

So the reason for the refusal to release FOI – embarrassment over dodgy data finding its way into speeches surely.

A lot of noise in the data, looking at one authority with a lot of NPS one parish has 500 allocations, several others with made NPs have zero.  It’s their choice of course.  This also means the distribution has a long tail.  A few NPs with a lot of allocations and many with none.  Again you need to drill down into the data to understand this.

Lets say there was a 10% uplift but demographically the requirement was +15%.  What are ministers saying, well done, or well done but must try harder?

For the many NPs that are for small villages without services so what if they have little housing, they are not good locations for lots of housing.

What are ministers trying to say with the 3 year rule.  Hey there is a great incentive to do an NP you can build less housing?  A pretty perverse incentive.  It would be better to apply a 5 year rule and apply a short 1 year moratorium whilst an NP is prepared providing it signs an MOU (in advance of the 1 year clock starting) with the LPA on appropriate housing numbers and then allocates sites to meet them.

NPS are a good thing but the theory that the conservatives promoted in the early years of the coalition  that NPs were the solution to uplifting meeting housing need and this could replace strategic allocations, no evidence for that at all.  Indeed there is mounting evidence that if you want to control rises in house prices large sites and large allocations are the only way to go.