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“Likelihood to be diagnosed or misdiagnosed” revisited: the Efficiency Index
  • Andrew Larner
Andrew Larner
Walton Centre

Corresponding Author:[email protected]

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Objectives: To calculate an “efficiency index” (EI) based on “numbers needed” metrics (specifically to diagnose and to misdiagnose) for cognitive screening instruments which are commonly used in suspected dementia, and to compare these values with those of a previously described “likelihood to be diagnosed or misdiagnosed” (LDM) metric also based on “numbers needed” metrics. Methods: Datasets from pragmatic test accuracy studies examining four brief cognitive screening instruments (Mini-Mental State Examination, MMSE; Montreal Cognitive Assessment, MoCA; Mini-Addenbrooke’s Cognitive Examination, MACE; Free-Cog) were analysed to calculate values for EI and LDM, and to examine their variation with test cut-off for MACE,. Findings: EI and LDM had similar values for all the screening instruments examined but EI was simpler to calculate than LDM. Both metrics showed similar maxima across a range of cut-offs for MACE. The differing score range of EI and LDM allowed the former, but not the latter, to be qualitatively classified as for likelihood ratios, with three of the tests (MMSE, MACE, Free-Cog) achieving a “moderate” increase in the likelihood of dementia diagnosis. Conclusions: The efficiency index (EI) metric indicates the utility or inutility of diagnostic tests in a way that is easily intelligible for both clinicians and patients, illustrating the inevitable trade-off between diagnosis and misdiagnosis.