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Screening and Diagnostic Tests
Published in Marcello Pagano, Kimberlee Gauvreau, Heather Mattie, Principles of Biostatistics, 2022
Marcello Pagano, Kimberlee Gauvreau, Heather Mattie
The term specificity/(1 - sensitivity) is called the negative likelihood ratio, and quantifies the change in the odds of not having the disease after a negative test result. As with the positive likelihood ratio, the negative likelihood ratio of a test increases as its specificity or sensitivity or both increase. Returning to our examples, for a test with sensitivity 0.9 and specificity 0.7 the negative likelihood ratio is . This indicates that if an individual tests negative, the odds of not having the condition increase by a factor of 7. For the Pap smear the negative likelihood ratio is , and for the chest radiograph it is .
Identifying cases of disease: Clinimetrics and diagnosis
Published in Milos Jenicek, Foundations of Evidence-Based Medicine, 2019
Likelihood ratios64–66 are appropriately named. The likelihood ratio of a positive test result is the probability of a particular positive test result given disease divided by the probability of the same result given no disease, i.e.
An evidence-based guide to cardiac catheterisation
Published in John Edward Boland, David W. M. Muller, Interventional Cardiology and Cardiac Catheterisation, 2019
Steven Faddy, Gary J. Gazibarich
The likelihood ratio indicates how many times more (or less) likely a patient with disease is to have a specific test result compared to a patient without disease. The positive likelihood ratio examines the positive test results and compares them in patients with disease to those without disease. The best diagnostic test to ‘rule in’ disease has a large positive likelihood ratio (>10). The negative likelihood ratio examines the negative results and compares them in patients without disease to those with disease. The best diagnostic test to ‘rule out’ disease has a very small negative likelihood ratio (<0.1).35 The likelihood ratio is independent of disease prevalence and allows the clinician to calculate the probability of disease for an individual patient.33
The validity of the ‘General Practice Physical Activity Questionnaire’ against accelerometery in patients with chronic kidney disease
Published in Physiotherapy Theory and Practice, 2022
Thomas J Wilkinson, Jared Palmer, Eleanor F Gore, Alice C Smith
A 2 × 2 table was constructed comparing GPPAQ results for all individuals with their accelerometer results as a criterion (n = 40), and validation tests were calculated using MedCalc (v19.1). Sensitivity was defined as the ability of GPPAQ to correctly identify as active those achieving the physical activity guidelines as assessed by accelerometery. Specificity was defined as the ability of GPPAQ to correctly identify as not active those not achieving the physical activity guidelines by accelerometery. Positive likelihood ratio is defined as sensitivity/1-specificity with Negative likelihood ratio defined as 1-sensitivity/specificity. Positive predictive value (PPV) is the probability that someone is ‘Active’ by accelerometery when also ‘Active’ on the GPPAQ. Negative predictive value (NPV) is the probability that a person is ‘Inactive’ by accelerometery when also ‘Inactive’ on the GPPAQ. Accuracy is the overall probability that the GPAPQ correctly classified a patient as either ‘Active’ or ‘Inactive.’ Sensitivity, specificity, PPV, and NPV are expressed as percentages. 95% confidence intervals (CI) for sensitivity, specificity, and accuracy are ‘exact’ Clopper-Pearson CI, CI for the likelihood ratios are calculated using the ‘Log method,’ CI for the predictive values are the standard logit CI. Differences in ‘accuracy’ between the GPPAQ and GPPAQ-WALK, between unemployed/retired and employed, and between males and females were explored by calculating the standard deviation from the 95% CI and using T-statistic testing.
Cervical spine thrust and non-thrust mobilization for the management of recalcitrant C6 paresthesias associated with a cervical radiculopathy: a case report
Published in Physiotherapy Theory and Practice, 2022
Christopher R. Hagan,, Alexandra R. Anderson,
This patient met the criteria for a clinical diagnosis of cervical radiculopathy with neurologic deficits consistent with a C6 nerve root dysfunction (Caridi, Pumberger, and Hughes, 2011; Wainner et al., 2003). It is believed that the patient history and physical examination are sufficient in making a CR diagnosis (Woods and Hilibrand, 2015). To further assist in this case, Wainner et al. (2003) developed a 4-item test cluster for CR which includes Spurling’s test, distraction test, ipsilateral cervical rotation <60 degrees, and positive upper limb tension test A for the median nerve. Specificity is 0.94 and positive likelihood ratio (LR) is 6.1 with 3 out of 4 positive tests, and specificity of 0.99 and a positive LR of 30.3 with 4 out of 4 positive tests (Wainner et al., 2003). Thorough subjective and objective examination is a cost-effective way to determine a clinical diagnosis of cervical radiculopathy.
Commentary: statistical analysis of 2 × 2 tables in biomarker studies 1) the four ‘indices of test validity’
Published in Biomarkers, 2022
Likelihood ratios combine the sensitivity and specificity into a single number. They also provide, using formulae based on Bayes’ theorem, a link between, the prior (the pre-test probability or prevalence) and posterior (post-test probability or PPV or NPV) probabilities of the test result for an individual case. The likelihood ratio can also be combined with the Pre-test Odds, using formulas based on Bayes’ theorem, to calculate the posterior probability values, PPV and NPV. The Likelihood Ratio can, therefore, be thought of as a multiplier to convert the pre-test odds of the condition (the prevalence) to the post-test odds (the positive predictive value or PPV). Likelihood Ratios can be derived for both quantitative and qualitative endpoints and are similar in interpretation to the Bayes factor developed as an alternative to classical hypothesis testing (Smith et al. 2019).