Photoplethysmography using a smartphone application for assessment of ulnar artery patency: a randomized clinical trial
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- Posted on: (25 July 2018)Page navigation anchor for Diagnostic accuracy in the presence of a rare outcomeDiagnostic accuracy in the presence of a rare outcome
- Eric McArthur, Statistician, Institute for Clinical Evaluative Sciences
Di Santo et al.(1) describe improved diagnostic accuracy for radial artery access eligibility using a smartphone application compared to the modified Allen test. Specifically, a superior overall diagnostic accuracy (91.8% vs. 81.7%) driven by an increase in specificity (93.0% vs. 82.8%).
Overall diagnostic accuracy (i.e. the proportion of individuals correctly classified) is advantageous as it is an easily calculable and interpretable measure of diagnostic performance. However, overall diagnostic accuracy is affected by disease prevalence. Holding sensitivity and specificity constant, a test’s overall diagnostic accuracy increases as disease prevalence decreases.
In the study by Di Santo et al., only 6 of 219 (0.3%) participants in the smartphone application group experienced the outcome. The limitations with overall diagnostic accuracy in this setting become apparent when you consider an alternative test where instead of using the smartphone application, every individual is classified as ‘test negative’. Such a scenario would classify all 219 participants as ‘test negative’, resulting in 213 true negatives, 6 false negatives, and no participants coded as ‘test positive’. This hypothetical test would have improved diagnostic performance compared to the smartphone application based on the two metrics described in the abstract by Di Santo et al., with an overall diagnostic accuracy of 97.3% and specificity of 100%.
Other measures of diagnostic accuracy e...
Show MoreDi Santo et al.(1) describe improved diagnostic accuracy for radial artery access eligibility using a smartphone application compared to the modified Allen test. Specifically, a superior overall diagnostic accuracy (91.8% vs. 81.7%) driven by an increase in specificity (93.0% vs. 82.8%).
Overall diagnostic accuracy (i.e. the proportion of individuals correctly classified) is advantageous as it is an easily calculable and interpretable measure of diagnostic performance. However, overall diagnostic accuracy is affected by disease prevalence. Holding sensitivity and specificity constant, a test’s overall diagnostic accuracy increases as disease prevalence decreases.
In the study by Di Santo et al., only 6 of 219 (0.3%) participants in the smartphone application group experienced the outcome. The limitations with overall diagnostic accuracy in this setting become apparent when you consider an alternative test where instead of using the smartphone application, every individual is classified as ‘test negative’. Such a scenario would classify all 219 participants as ‘test negative’, resulting in 213 true negatives, 6 false negatives, and no participants coded as ‘test positive’. This hypothetical test would have improved diagnostic performance compared to the smartphone application based on the two metrics described in the abstract by Di Santo et al., with an overall diagnostic accuracy of 97.3% and specificity of 100%.
Other measures of diagnostic accuracy exist that are not as susceptible to disease prevalence, including the diagnostic odds ratio and Youden’s index.(2) These measures describe the improved diagnostic performance associated with the smartphone application compared to the modified Allen test without being as influenced by the low event rate (diagnostic odds ratio 13.2 vs. 1.6 and Youden’s index 0.43 vs. 0.08).
References
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1. Di Santo, Pietro, et al. "Photoplethysmography using a smartphone application for assessment of ulnar artery patency: a randomized clinical trial." CMAJ 190.13 (2018): E380-E388.
2. Šimundić, Ana-Maria. "Measures of diagnostic accuracy: basic definitions." EJIFCC 19.4 (2009): 203.Competing Interests: None declared.
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