A researcher is conducting a case-control study on the association between oral contraceptive use and venous thromboembolism (VTE) in Indian women. After data collection, the analysis shows a strong association (OR = 3.2, 95% CI 2.1–4.8). However, the researcher notices that cases were recruited from tertiary care centers (where VTE patients are more likely to be hospitalized), while controls were recruited from the community. What is the most appropriate next step to address this potential bias?