Journal article: Electronic health records (EHRs) are intended to reduce healthcare costs and improve the quality of care. Nevertheless, usability issues common to EHRs have been identified. In this paper, we investigate these usability issues for social vulnerability codes. Using the acute care EHR and the rehabilitation care EHR databases, hospital stays of 800'000 patients are studied. This article highlights the differences in coding processes between public and private institutions observed when there are different incentives to code. Furthermore, it shows that the differences in coding are not random but depend on the coding strategy. This article emphasises that the reuse of data leads to biases in interpretation. Using the example of social vulnerability alerts policymakers to the need to consider these differences in coding processes when decisions are based on EHR information. Otherwise, this process of coding differences in social vulnerability may exacerbate social inequalities rather than reduce them.