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Related Experiment Video

Updated: Apr 29, 2026

A New Portable In Vitro Exposure Cassette for Aerosol Sampling

A New Portable In Vitro Exposure Cassette for Aerosol Sampling

Published on: February 22, 2019

Delayed Exposures and Pre-Exposure Periods in Self-Controlled Case Series Studies.

Heather Whitaker^1,2, Yonas Ghebremichael Weldeselassie^2,3, Paddy Farrington²

¹Modelling Division, UK Health Security Agency, London, UK.

Statistics in Medicine

|April 27, 2026

Summary

The self-controlled case series (SCCS) method assumes exposures don't depend on the event. This study examines how delayed exposures, like vaccines, affect SCCS estimates and offers recommendations for analysis.

Keywords:

adverse event bias exposure delay pre‐exposure period self‐controlled case series vaccine

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Area of Science:

Epidemiology
Biostatistics

Background:

The self-controlled case series (SCCS) method is widely used for observational safety studies.
A core assumption is that exposure occurrence is independent of the event of interest.
Vaccine or treatment deferral after an adverse event violates this assumption.

Purpose of the Study:

To investigate the impact of exposure deferment on SCCS relative incidence estimates.
To evaluate the effectiveness of including a pre-exposure window in SCCS models.
To provide practical guidance for handling delayed exposures in SCCS analyses.

Main Methods:

Theoretical analysis in a simplified setting.
Simulation studies for realistic scenarios.
Evaluation of SCCS model adjustments for delayed exposures.

Main Results:

Delayed exposures can bias SCCS relative incidence estimates.
No adjustment is needed if delayed exposures fall within the observation period.
Adjustments or alternative models may be necessary if exposures are delayed beyond the observation period.

Conclusions:

The timing of exposures relative to health events is critical for SCCS validity.
Sensitivity analyses are recommended to assess the impact of exposure deferment.
The SCCS model for event-dependent exposures may be more appropriate in certain situations.