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An R-Based Landscape Validation of a Competing Risk Model

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Risk expression using likelihood ratios and natural frequencies in Bayesian inference tasks-a preregistered

Philipp Schulz¹, Odette Wegwarth^1,2, Helge Giese³

¹Heisenberg Chair for Medical Risk Literacy & Evidence-Based Decisions, Charité - Universitätsmedizin Berlin, Charitéplatz 1, 10117, Berlin, Germany.

BMC Medical Education

|April 9, 2025

Summary

Medical students better understand sequential diagnostic tests using odds and likelihood ratios (odds/LR). Natural frequencies are superior for single tests, but odds/LR improve interpretation of multiple tests for clinical decision-making.

Keywords:

Bayesian reasoning Conditional probabilities Natural frequencies Odds Positive predictive value

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Area of Science:

Medical Education
Diagnostic Test Interpretation
Clinical Decision-Making

Background:

Medical students require strong diagnostic test interpretation skills for informed decision-making.
Natural frequencies are standard for single diagnostic tests but may be less effective for sequential testing.
This study investigates odds and likelihood ratios (odds/LR) as an alternative for sequential diagnostic test interpretation.

Purpose of the Study:

To compare the effectiveness of natural frequencies versus odds/LR for calculating positive predictive values (PPV) of single and sequential diagnostic tests.
To assess the subjective comprehensibility of these two formats among students.

Main Methods:

A randomized-controlled crossover trial involving 167 medical and 162 psychology students.
Participants calculated PPVs for single and sequential diagnostic tests using either natural frequencies or odds/LR.
Primary outcome: proportion of correctly calculated PPVs; Secondary outcome: subjective comprehensibility.

Main Results:

Natural frequencies yielded higher correct PPVs for single tests (36.2% vs 21.6%).
Odds/LR resulted in significantly more correct PPVs for sequential tests (10.6% vs 4.9%).
Students found natural frequencies more comprehensible than odds/LR.

Conclusions:

Odds/LR may enhance medical students' understanding of sequential diagnostic tests.
Integrating odds/LR alongside natural frequencies could improve diagnostic decision-making skills.
Further education on odds/LR can benefit medical students' interpretation of complex diagnostic scenarios.