The Observed Depreciation Method (ODM) has the advantage of reflecting a building’s maintenance condition and the degree of deterioration in finishes and facilities based on on-site inspections. However, it has continuously faced criticism regarding...
The Observed Depreciation Method (ODM) has the advantage of reflecting a building’s maintenance condition and the degree of deterioration in finishes and facilities based on on-site inspections. However, it has continuously faced criticism regarding its reliability due to the potential for subjective judgment by appraisers. Despite this, both domestic and international studies that systematically analyze the ODM remain extremely limited. Accordingly, this study aims to empirically identify the factors affecting the reliability of building appraisals applying the ODM and to enhance the reliability of appraisal outcomes.
To achieve this objective, a two-track research design combining quantitative and qualitative analyses was employed. First, in-depth interviews were conducted with a total of 23 experts—12 licensed appraisers, 6 academics, 1 legal professional, and 4 representatives from the appraisal association—to identify practical issues and reliability-related factors associated with the ODM. Based on the interview findings, theoretical considerations, and a review of prior studies, eight variables influencing reliability were systematically structured.
These variables were defined as follows: (1) the degree of restraint in using the method due to subjectivity, (2) the degree of ambiguity in appraisal rationale, (3) the level of professional knowledge regarding building exteriors and related aspects, (4) the ease of collecting construction cost data, (5) the difficulty of analyzing construction cost data, (6) the necessity of on-site inspection checklists, (7) the necessity of criteria for each depreciation item, and (8) the adjustment of depreciation rates in response to client demands. All variables were derived through expert interviews and clearly defined through operationalization processes grounded in appraisal practice.
Based on these variables, a survey was conducted among 285 licensed appraisers nationwide, and multiple regression analysis was performed. The results indicated that “adjustment of depreciation rates in response to client demands,” “level of professional knowledge regarding building exteriors,” “ease of collecting construction cost data,” and “degree of restraint due to subjectivity” had statistically significant positive effects on the reliability and fairness of building appraisals applying the ODM. In contrast, institutional and procedural factors—such as “ambiguity in appraisal rationale,” “difficulty in analyzing construction cost data,” “necessity of on-site inspection checklists,” and “necessity of itemized depreciation criteria”—did not show statistically significant effects.
In the qualitative analysis, content analysis was conducted using open-ended responses from 81 appraisers and additional interviews with 11 experts focusing on improvement measures. Although “necessity of on-site inspection checklists” and “necessity of itemized depreciation criteria” were not significant in the regression analysis, the content analysis revealed that both practitioners and experts strongly perceived the need to improve the depreciation adjustment framework in practice.
This study holds significant academic and practical value as the first empirical research to directly examine the ODM as an independent analytical subject and to systematically structure and quantitatively verify the factors affecting its reliability. The findings suggest institutional and practical directions for improving appraisal reliability and fairness, including strengthening appraisers’ architectural expertise, ensuring independence to enhance ethical standards, improving access to construction cost data, introducing on-site inspection checklists, and establishing clearer criteria for depreciation judgments. Ultimately, the study is expected to contribute positively to the protection of property rights and the formulation of equitable real estate policies.