External assurance of the VOA automated valuation model (AVM): VOA response
This page sets out the VOA response to external review and assurance of the VOA AVM developed to support Wales Council Tax reform.
Documents
Details
Throughout the model development process the VOA drew on external expertise. Critical friends from the Centre for Appraisal Research and Technology, experts in mass appraisal provided advice during the model development, producing the attached reports.
The VOA also commissioned the Professional Consulting Service (PCS) of the International Association of Assessing Officers (IAAO), as a recognised world leading authority on AVMs, to carry out a review of the model. The IAAO produced a full report.
The critical friend reports, and the IAAO review report, assured and endorsed the model’s development and its outputs.
They also highlighted areas for further development or consideration. Based on these, and from further internal review, the VOA have a series of developments to the model in progress:
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Refining our ratio studies to include confidence intervals and additional measures, also testing model performance on more recent sales.
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Testing additional variables in the regression model and exploring alternative spatial techniques.
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Further improving the comparables model to give more useful comparables and better record the link between valuer judgement and the model scores and weightings, then re-considering how it is used and fed into reliability scores.
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Further consideration of how to utilise model estimates to produce reliable defendable bands, particularly where model estimates in close proximity can vary due to more minor changes in property characteristics, such as plot size or parking facilities.