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honeybadger

House price per square metre plotted

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Anna Powell Smith, a developer/data scientist, has created a plot of house prices per square metre, by combining Land Registry data with area data from Energy Performance of Buildings Data, see here:

https://houseprices.anna.ps/

I think the Energy Performance data has only recently been made available, though I'm not 100% sure about that. It is at the following link, but you need to register:

https://epc.opendatacommunities.org/

It should be possible to use the same idea to produce more accurate plots of price changes over time than is possible with the LR data alone.

 

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That's excellent work. 

Particularly illuminating to drag the slider on the key at the top right, to not show the cheapest band - and observing the correlation with where those areas are.

Small gap in the data just east of Birmingham Airport :-)

 

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I've turned my weasel words ('It should be possible...') into reality, by joining the LR data together with the Energy Performance Certificate data to produce plots of price per square metre over time (for London boroughs, my area of interest). Some may regard this as an odd way to spend an Easter holiday weekend, but I think the results are nice, and as far as I'm aware, no one else has done this.

Quick summary of methodology: for each Land Registry transaction, try to find the property in the EPC data, and if a match is found, extract the total floor area. A match may not be found for a couple of reasons:

(1) An EPC may never have been done.

(2) There may be small differences in the way the address was entered in the two datasets.

It's impossible to do anything about (1).

For (2), I tried to normalize the addresses as much as possible by deleting unnecessary punctuation and extra spaces, and converting to uppercase only. This is far from ideal, but nevertheless, I'm getting a match for roughly two thirds of the LR transactions in recent years. For some reason, the match percentage is worse before and including 2008. In particular something odd happens in 2008 itself when the match percentage is extremely low. The effect of this can be seen in the plots, where it introduces a lot of noise. I guess this is something to do with the EPC dataset.

One this is done, for each (month, borough), add up total price paid and divide by the sum of the total floor area, over all properties. This is the mean price per square metre.

Here is the plot for period London flats, with boroughs ordered by value in the most recent month (most expensive first). Data for Feb 2017 in the LR data is discarded since it is incomplete. I kept Jan 2017 which is also incomplete, but less so.

london_mean_period_flat.pdf

Stagnation is evident since 2015 in the more expensive boroughs, with declines in some. We know this is happening, but hopefully this picture adds something new. Normalizing by per-square-metre value should mean that the plots are less noisy than just taking the mean of all flats in a borough, for instance.

 

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.

Quote

In particular something odd happens in 2008 itself when the match percentage is extremely low. The effect of this can be seen in the plots, where it introduces a lot of noise. I guess this is something to do with the EPC dataset.

Maybe something to do with using the stats to try to disguise what was happening at the time (the start of the house price collapse)?  

It might sound a stretch but it's bit of a coincidence that it happened in 2008 just when house prices were starting to rapidly fall.

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3 minutes ago, billybong said:

.

Maybe something to do with using the stats to try to disguise what was happening at the time (the start of the house price collapse)?  

It might sound a stretch but it's bit of a coincidence that it happened in 2008 just when house prices were starting to rapidly fall.

I must admit something similar occurred to me, but I do think it's a bit of stretch. I may try to dig into the data at some point to see what's going on.

 

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Nice work. I've always wanted to see UK prices expressed this way. Isn't this quite a standard approach in many other countries?

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