Dispersion and Comparable Spread
Variation among the sales behind the estimate
Dispersion measures how widely the sold prices of comparable homes scatter around their average. Propbar's valuation model reports it as a band: low, moderate, high or very high. The band derives from the forecast standard deviation, a standard measure of automated valuation accuracy. The comparable sales behind the band come from each UK nation's own sold-price register.
What This Means
High dispersion is a statement about the neighbourhood's sales evidence, not about this property. It means nearby homes that look alike sold at prices far apart. The estimate above is a weaker guide as a result, and its range widens to say so. Where the band reads high or very high, Propbar overrides the confidence badge. Mixed streets, few recent sales and unusual homes all push dispersion up. A low band does not make the estimate right; it means the evidence behind it is consistent.
Score Ranges
Low dispersion
Smallest forecast standard deviationComparable homes nearby sold at closely similar prices, so the evidence is consistent.
Moderate dispersion
Middling forecast standard deviationPrices vary about as much as they usually do on a mixed residential street.
High dispersion
Large forecast standard deviationComparable prices sit far apart, and the estimate rests on conflicting evidence.
Very high dispersion
Largest forecast standard deviationComparable prices disagree so much that the model cannot locate a market level.
Practical Advice
- Ask the estate agent for the sold prices and dates of the three closest comparable homes.
- Ask your surveyor which comparables they relied on, and why they set the outliers aside.
- Ask your mortgage broker how the lender's valuer treats a street where comparable prices disagree this widely.
Key Points
- A forecast standard deviation of 10% on a £500,000 estimate means roughly a two-in-three chance the true price sits between £450,000 and £550,000.
- The model rates confidence High and the band reads very high; the report shows Low instead, and notes that comparable prices show a very high dispersion in the local area.
Additional Information
Alongside the band, the report prints a coefficient of variation and a same-bedroom spread, both as percentages. The first measures scatter across the whole comparable set. The second isolates homes with the same bedroom count, so a like-for-like gap is visible rather than a size difference.