What drives appraisal adjustments in residential valuation? Paired evidence from Ho Chi Minh City

Purpose This study aims to examine the determinants and within-report consistency of appraisal adjustment coefficients in residential land valuation and develops a regression-based screening framework for quality-control review. Design/methodology/approach Using 168 paired subject–comparable records from 56 valuation reports in Ho Chi Minh City, we estimated ordinary least squares regression with report-clustered standard errors and within-report fixed-effects analysis. Residual-based screening thresholds classified reports into four quality-control tiers. Findings Location-type mismatch and area dissimilarity are the primary drivers of adjustment magnitude, with each one-tier location difference corresponding to a 4.6-percentage-point change. Within-report analysis supports broad proportionality between adjustments and composite dissimilarity, and the framework flags 25 per cent of reports for review. Leave-one-report-out validation showed bounded out-of-sample value (RMSE 0.079, with about 82 per cent of predictions within ±0.10). Research limitations/implications The sample is from a single valuation firm in one former district; multi-firm replication is needed. The adjustment coefficient is an overall ratio, not a decomposition of individual attribute-level adjustments. Practical implications The screening framework offers valuation firms a first-stage internal review tool. The identified determinants provide an empirical reference point for regulators implementing Vietnam's 2024 Valuation Standards. Originality/value This study provides rare paired subject–comparable evidence from an emerging housing market, introduces a within-report proportionality test exploiting the nested structure of multi-comparable reports and translates findings into a practical quality-control tool for residential valuation practice.