The receiver operating characteristic (ROC) curve is a measure of diagnostic efficiency, which is obtained by graphically plotting a series of true positive rates (sensitivity) against false positive rates (1 – specificity) for a binary outcome system. The ROC curve is a method to visualize the performance of a test with binary outcomes (+ / -) graphically. The area under the ROC (AUROC) curve is equal to the … Continue reading Diagnostic Efficiency
Post-test probability: is the probability of the presence of a disease after a confirmatory diagnostic test. Method I: Let us estimate post-test probability by hand calculation using the data from the study by Capra et al (1). To do this, we need to know the pre-test probability and the positive likelihood ratio values. For this purpose, let us assume the pre-test probability as 0.55. And, we will … Continue reading Post-test Probability
Let us continue using the data from the study by Capra et al (1). The likelihood ratio is the percentage of diseased individuals with a given test result divided by the percentage of healthy individuals with the same test result (2). The likelihood ratios (positive and negative) can be calculated by using the following formulae (2): + LR = sensitivity / (1- specificity) = True positive rate / … Continue reading Likelihood Ratios
Let us continue our Predictive Values analysis using data from Capra et al (1). After a confirmed MRI diagnosis, we may have the following questions: What is the probability that the patient with a positive MRI result has the disease? or What is the proportion of patients with positive MRI results have the disease? Calculating the post-test probabilities (in other terms, post-test likelihood values or positive/negative predictive values) will help … Continue reading Predictive Values
Now, let us calculate the False/Error Rates of the SLR test when compared against the gold standard MRI test results (1). The false positive rate of the SLR test (Type I error) is calculated as the ratio between the number of negative MRI results wrongly determined as positive results by the SLR test and the total number of negative MRI results. The false negative rate of the SLR test (Type II error) is … Continue reading False/Error Rates
