Validating a threshold of ocular gaze deviation for the prediction of acute ischaemic stroke

Re: Validating a threshold of ocular gaze deviation for the prediction of acute ischaemic stroke

“…Re: Validating a threshold of ocular gaze deviation for the prediction of acute ischaemic stroke SirdI am no neuroradiologist, but my attention was caught by the recent study from McKean et al 1 The title promised the "validation" of a radiological "prediction" model, something that I am very interested in. A "prediction" or "prognostic" model usually involves a measurement (or combination of measurements) made on a patient which is used to predict future outcomes.…”

“…In the present case, the authors measured the degree of ocular gaze deviation (OGD) and used this to predict whether the patient did or did not have an acute ischaemic stroke. 1 Prognostic models are "developed" using data collected on patients who do and do not have the outcome of interest and are only clinically useful if they are sufficiently predictive. It is also important to know that a model developed and accurate in hospital X also works for patients in hospital Y.…”

“…2 Alas, I was to be disappointed: McKean and colleagues describe a model developed using data collected from 517 patients presenting to a single hospital, with no attempt to validate predictive accuracy either there or elsewhere. 1 In any event, I was struck by the apparently poor predictive capabilities of the data. The authors conclude that "Significant OGD >11.95 has a high specificity for acute infarct" and that "This threshold may provide a helpful additional sign in the detection of subtle acute infarct".…”

“…The authors conclude that "Significant OGD >11.95 has a high specificity for acute infarct" and that "This threshold may provide a helpful additional sign in the detection of subtle acute infarct". 1 Specificity describes the accuracy with which a test identifies patients without disease and cannot be evaluated sensibly without simultaneously considering sensitivity, the accuracy with which the test identifies patients with disease. At their OGD threshold of 11.95, specificity for infarct is 95.9% but sensitivity is 17.3%.…”

“…At their OGD threshold of 11.95, specificity for infarct is 95.9% but sensitivity is 17.3%. 1 How "helpful" is a diagnostic test used at a threshold that will miss more than four out of every five patients with the target condition? Not very, I would argue, especially when research has shown that patients and their doctors value gains in sensitivity far over and above corresponding gains in specificity.…”