Transporting: What Is It and How Do You Do It?

Area of Science:

• Epidemiology
• Biostatistics
• Health Services Research

Background:

• External validity, encompassing generalizability and transportability, is crucial for applying research findings.
• Historically, these concepts were discussed qualitatively, lacking formal definitions and analytical methods.
• Recent advancements aim to formally define and analytically address transportability.

Purpose of the Study:

• To provide an overview of methodological developments in transportability.
• To offer a tutorial on key steps in the transportability process.
• To distinguish transportability from generalizability and external validity.

Main Methods:

• Defining core conditions for transporting treatment effects.
• Outlining approaches to identify sufficient adjustment sets.
• Designing estimators for transported treatment effects.
• Illustrating methods with a case study on breast cancer adjuvant chemotherapies.

Main Results:

• Formal definitions and analytical methods for transportability have been developed.
• Case study demonstrates applying transportability methods to real-world data.
• Distinction between transportability and generalizability is clarified.

Conclusions:

• Methodological strides have been made in formally defining and analyzing transportability.
• Analytic methods are now available for estimating transported treatment effects under defined conditions.
• Transportability is a key component for robust epidemiological inference.