Confounding and exposure trends in case-crossover and case-time-control designs

Area of Science:

• Epidemiology
• Biostatistics
• Public Health Research

Background:

• Observational epidemiological studies, including case-crossover and case-time-control designs, are prone to confounding.
• Confounding by indication is a specific challenge in these study designs.
• Case-crossover studies mitigate fixed confounding but may introduce bias from exposure time trends.

Purpose of the Study:

• To evaluate the confounding properties of case-time-control studies in comparison to traditional and case-crossover designs.
• To understand how time-varying confounders and other biases affect the validity of different epidemiological study designs.

Main Methods:

• Theoretical analysis of confounding in case-crossover and case-time-control study designs.
• Comparison of bias introduced by fixed and time-varying confounders across different epidemiological approaches.
• Assessment of assumptions regarding unmeasured confounders and carryover effects in each study design.

Main Results:

• Case-time-control studies can correct for time trends but may introduce new confounding if uncontrolled factors are present.
• The degree of confounding in case-time-control studies relative to ordinary and case-crossover studies is context-dependent.
• Both case-time-control and case-crossover studies share assumptions about the absence of carryover effects and are susceptible to misclassification bias.

Conclusions:

• The relative effectiveness of case-time-control studies in reducing confounding depends on the specific interplay of confounders, exposures, and disease.
• Case-time-control and case-crossover designs require careful consideration of potential biases, similar to traditional epidemiological studies.
• Assumptions of no unmeasured confounders and no carryover effects are critical for the validity of case-time-control and case-crossover analyses.