A fair comparison holds everything constant except the thing you are comparing: same period, same dataset, same geography size, same property type. Get any one of those wrong and you will produce a confident answer to a question you did not ask.
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How to compare two areas fairly using open data
A fair comparison holds everything constant except the thing you are comparing: same period, same dataset, same geography size, same property type.
- 1 min read
- Updated 21 September 2026
Part 1 of 4
The four things to hold constant
| Hold constant | What goes wrong if you do not |
|---|---|
| Time period | Comparing one area's spring against another's autumn picks up seasonality, not place |
| Geography size | An outward district against a full postcode compares a town with a street |
| Property type | A flat-heavy district always looks cheaper than a house-heavy one |
| Source and its publication schedule | Two datasets updated at different times can disagree purely on timing |
State your sample sizes on both sides. Twelve sales against six hundred is not a comparison, it is one solid figure next to a rumour — and the only way a reader can tell is if you say so.
Where a dataset does not cover one of your two areas, say that rather than substituting a proxy. Several UK datasets stop at national borders: Land Registry price paid data covers England and Wales, the police.uk feed excludes Scotland and Northern Ireland, and the English indices of deprivation are England-only.
Part 2 of 4
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Part 3 of 4