Prior probability (the pretest best guess) affects predictive values of diagnostic tests.
Summary of "Prior probability (the pretest best guess) affects predictive values of diagnostic tests."
Authors who publish evaluations of dichotomous (yes/no) diagnostic tests often include the predictive values of their test at a single prior probability (eg, the prevalence of the target disease within the evaluation data set). The objectives of this technical note are to demonstrate why single-probability predictive values are misleading and to show a better way to display positive predictive values (PPV) and negative predictive values (NPV) for a newly evaluated test. Secondly, this technical note will show readers how to calculate predictive values from only sensitivity and specificity for any desired prior probability. As prior probability increases from 0% to 100%, PPV increases from 0% to 100%, but NPV goes in the opposite direction (drops from 100% to 0%). Because prior probabilities vary so greatly across situations, predictive values should be provided in publications for the full range of potential prior probabilities (if provided at all). This is easily done with a 2-curve graph displaying the predictive values (y-axis) against the prior probability (x-axis).
Affiliation
Section of Epidemiology, Department of Population Medicine & Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA.
Journal Details
This article was published in the following journal.
Name: Veterinary clinical pathology / American Society for Veterinary Clinical Pathology
ISSN: 0275-6382
Pages:
Links
- PubMed Source: http://www.ncbi.nlm.nih.gov/pubmed/21554365
- DOI: http://dx.doi.org/10.1111/j.1939-165X.2011.00315.x
Medical and Biotech [MESH] Definitions
Predictive Value Of Tests
In screening and diagnostic tests, the probability that a person with a positive test is a true positive (i.e., has the disease), is referred to as the predictive value of a positive test; whereas, the predictive value of a negative test is the probability that the person with a negative test does not have the disease. Predictive value is related to the sensitivity and specificity of the test.
Likelihood Functions
Functions constructed from a statistical model and a set of observed data which give the probability of that data for various values of the unknown model parameters. Those parameter values that maximize the probability are the maximum likelihood estimates of the parameters.
Confidence Intervals
A range of values for a variable of interest, e.g., a rate, constructed so that this range has a specified probability of including the true value of the variable.
Statistical Distributions
The complete summaries of the frequencies of the values or categories of a measurement made on a group of items, a population, or other collection of data. The distribution tells either how many or what proportion of the group was found to have each value (or each range of values) out of all the possible values that the quantitative measure can have.
Risk
The probability that an event will occur. It encompasses a variety of measures of the probability of a generally unfavorable outcome.
PubMed Articles
Background: The precision of clinical diagnosis of skin tumors is not commonly measured and, therefore, very little is known about the diagnostic ability of clinicians. Objective: This study aimed to...
Distinguishing true from false positives in genomic studies: p values.
Distinguishing true from false positive findings is a major challenge in human genetic epidemiology. Several strategies have been devised to facilitate this, including the positive predictive value (P...
Direct bronchoprovocation challenges (eg, methacholine), which act directly on a specific airway smooth muscle receptor, are the most commonly performed challenge tests. Cut points have been arbitrari...
Transition items are a popular approach to determine the clinical significance of patient-reported change. These items assume that patients (1) arrive at a change evaluation by comparing posttest and...
Suspected carpal tunnel syndrome: Do nerve conduction study results and symptoms match?
OBJECTIVE: To evaluate the diagnostic utility of nerve conduction studies (NCSs) by examining a population with a high pretest probability of carpal tunnel syndrome (CTS), including bilaterally and un...
Clinical Trials
The purpose of this study is to evaluate if the implementation of quantitative pretest probability assessment will significantly reduce the unnecessary use of the intra-emergency departmen...
Neonatal Procalcitonin Intervention Study
In neonates, clinical signs and symptoms associated with early-onset sepsis are non-specific and currently available tests have poor positive and negative predictive values. The investigat...
Understanding Probability in Children
To make medical decisions involving pros and cons, one also has to understand probability and percentages. This is a preliminary study to evaluate the ability of children to understand pro...
Predictive Values of Serotonergic Alterations for Outcome - 2
The purpose of this study is to evaluate the predictive value of serotonergic alterations for outcome.
Impact of Oximetry on Hospitalization in Acute Bronchiolitis
To determine, in previously healthy infants 6 weeks to 12 months of age, diagnosed with acute bronchiolitis and monitored by hourly oximetry, if the probability of hospitalization within 7...
