Communicating Risk: Developing an "Efficiency Index" for Dementia Screening Tests.

Andrew J Larner

doi:10.3390/brainsci11111473

Abstract

Diagnostic and screening tests may have risks such as misdiagnosis, as well as the potential benefits of correct diagnosis. Effective communication of this risk to both clinicians and patients can be problematic. The purpose of this study was to develop a metric called the “efficiency index” (EI), defined as the ratio of test accuracy and inaccuracy, to evaluate screening tests for dementia. This measure was compared with a previously described “likelihood to be diagnosed or misdiagnosed” (LDM), also based on “numbers needed” metrics. Datasets from prospective pragmatic test accuracy studies examining four brief cognitive screening instruments (Mini-Mental State Examination; Montreal Cognitive Assessment; Mini-Addenbrooke’s Cognitive Examination (MACE); and Free-Cog) were analysed to calculate values for EI and LDM, and to examine their variation with test cut-off for MACE and dementia prevalence. EI values were also calculated using a modification of McGee’s heuristic for the simplification of likelihood ratios to estimate percentage change in diagnostic probability. The findings indicate that EI is easier to calculate than LDM and, unlike LDM, may be classified either qualitatively or quantitatively in a manner similar to likelihood ratios. EI shows the utility or inutility of diagnostic and screening tests, illustrating the inevitable trade-off between diagnosis and misdiagnosis. It may be a useful metric to communicate risk in a way that is easily intelligible for both clinicians and patients.

Highlights

No medical treatment or test is without potential harms as well as benefits, and associated with risk
Considering diagnostic or screening tests, performance is typically described by comparison with a reference standard, such as a criterion diagnosis or a reference test, by constructing a 2 × 2 contingency table, such that all (N) index test results may be crosstabulated as true positive (TP), false positive (FP), false negative (FN), or true negative (TN)
The primary aim of this study was to examine the utility of efficiency index” (EI) and compare it to the previously defined likelihood to be or misdiagnosed” (LDM) parameter when applied to test accuracy studies of several brief cognitive screening instruments (CSIs), namely Mini-Mental State Examination (MMSE) [17], Montreal Cognitive Assessment (MoCA) [18], Mini-Addenbrooke’s Cognitive Examination (MACE) [19], and

Summary

Introduction

No medical treatment or test is without potential harms as well as benefits, and associated with risk Communicating such risk to patients for the purpose of shared decision making has attracted much attention and research in recent times, for example into the most appropriate methods by which to achieve such communication effectively. Guidance on both verbal and numerical qualifiers of risk has appeared [1,2]. From this standard 2 × 2 contingency table (Figure 1), various parameters of test discrimination may be calculated, many of which are familiar to clinicians as descriptors of test performance, such as sensitivity (Sens; or true positive rate) and specificity (Spec; or true negative rate), positive and negative predictive values, and positive and negative likelihood ratios (LR+, LR−) [4]

Objectives

Methods

Conclusion