Clinical Scorecard: Addressing Time-Varying Confounding in Self-Controlled Case Series Using Active Comparators: Insights and Guidance

At a Glance

Key Highlights

• SCCS inherently controls for time-invariant confounding by comparing exposed and unexposed periods within individuals.
• Time-varying confounding by indication remains a challenge in SCCS and can bias results if not addressed.
• Incorporation of active comparators in SCCS reduces bias from unmeasured time-varying confounders by leveraging similar confounding patterns.

Guideline-Based Recommendations

Diagnosis

• Identify potential time-varying confounders such as indications that change over time and may influence both exposure and outcome.

Management

• Incorporate active comparators in SCCS designs to address time-varying confounding by indication.
• Use methods such as comparing regression coefficients or nested regression models to derive active comparator rate ratios.

Monitoring & Follow-up

• Evaluate assumptions of SCCS including independence of recurrent events and that events do not affect future exposure or observation time.
• Assess the appropriateness of the active comparator to ensure similar time-varying confounding patterns.

Risks

• Potential bias if active comparator is not well chosen or if SCCS assumptions are violated.
• Misinterpretation of causal effects if time-varying confounding is not adequately controlled.

Patient & Prescribing Data

Patients with drug exposures and outcomes recorded in longitudinal clinical databases, e.g., CPRD

Active comparator methods improve robustness of causal inference in drug safety studies by mitigating bias from unmeasured time-varying confounding.

Clinical Best Practices

• Apply SCCS design for within-individual comparisons to control for time-invariant confounding.
• Select active comparators with similar indications and time-varying confounding patterns to the drug of interest.
• Use formal statistical methods (ratio of regression coefficients or nested models) to incorporate active comparators in SCCS.
• Carefully assess SCCS assumptions and the potential impact of time-varying confounders on study validity.
• Leverage large clinical databases such as the UK CPRD for application of these methods.

References

• Self-Controlled Case Series Method
• Clinical Practice Research Datalink (CPRD)
• Active Comparator Methods in Pharmacoepidemiology