Items tagged “research”
20 results found
Article
Sensitivity
Sensitivity is one of the 4 basic diagnostic test metrics in addition to specificity, positive predictive value and negative predictive value. Sensitivity is a measure of how good a diagnostic test is at detecting disease when it is present and is calculated by dividing the number of true positi...
Article
Specificity
Specificity is one of the 4 basic diagnostic test metrics in addition to sensitivity, positive predictive value and negative predictive value. Specificity is a measure of how good a diagnostic test is at identifying people who are healthy and is calculated by dividing the number of true negative...
Article
Positive predictive value
Positive predictive value (PPV) is one of the 4 basic diagnostic test metrics in addition to sensitivity, specificity and negative predictive value. Positive predictive value is a measure of how often someone who tests positive for disease actually has disease and is calculated by dividing the n...
Article
p-value
A p-value is the probability of observing a difference between groups at least as extreme as what was observed. Since a p-value is calculated assuming that the null hypothesis (H0) is true, the expectation is that there is no difference between the groups being evaluated. The process of evaluati...
Article
Receiver operating characteristic curve
The receiver operating characteristic (ROC) curve is a statistical relationship used frequently in radiology, particularly with regards to limits of detection and screening.
The curves on the graph demonstrate the inherent trade-off between sensitivity and specificity:
y-axis: sensitivity
x-a...
Article
Nervus terminalis
The nervus terminalis, also referred to as cranial nerve zero, cranial nerve XIII, zero nerve, nerve N or NT, is a previously unnumbered cranial nerve, most rostral of all cranial nerves.
Gross anatomy
It is a bilateral bundle of nerve fibers, which runs in the subarachnoid space from the medi...
Article
Power
The power of a clinical trial is the probability that the trial will find a difference between groups if there is one. Power can be defined as the probability of a true positive trial result and is often written as:
power = (1 - β)
where β is the probability of missing a difference between gro...
Article
ANOVA
ANOVA (ANalysis Of VAriance) is a statistical technique commonly seen in radiology research.
ANOVA analyzes are conceptually similar to the student t-test, but involve comparison of multiple groups at once. The alternative to an ANOVA would be multiple head-to-head t-tests, but this would likel...
Article
Case report
Case reports are a type of radiology research literature. They belong to the class of descriptive studies.
Purpose
The purpose of a radiology case report is to describe the patient history, clinical course, and imaging for a notable or unusual case. The case may be intended to aid other practi...
Article
Case series
A case series is essentially a collection of case reports around a common theme. It belongs to the class of descriptive studies.
Structure
A case series typically contains:
a short introduction
the series of cases
patient history, presentation, imaging, and clinical course are described in ...
Article
Likelihood ratios
Likelihood ratios (LR) are an alternative to positive and negative predictive values for estimating the likelihood of disease after diagnostic testing. The general formula for a likelihood ratio is the probability (P) that someone with a disease will have a particular test result divided by the ...
Article
Pearson's chi-squared test
The Pearson's chi-squared test is one of the most common statistical tests found in radiology research. It is a type of non-parametric test, used with two categorical variables (not continuous variables).
Concept
The heart of the chi-squared test is a 2 x 2 contingency table.
We usually have ...
Article
Paired t-test
The paired t-test is the appropriate method when the researcher takes an experimental group, measures the baseline, subjects the members to an intervention, and then measures the results.
Testing in a before-and-after manner like this ("matched data" or "repeated measures") requires a different...
Article
Kappa
Kappa is a nonparametric test that can be used to measure interobserver agreement on imaging studies. Cohen's kappa compares two observers, or in the case of machine learning can be used to compare a specific algorithm's output versus labels. Fleiss' kappa assesses interobserver agreement betwee...
Article
Confusion matrix
Confusion matrices, a key tool to evaluate machine learning algorithm performance in classification, are a statistical tool.
Contingency tables, a type of confusion matrix, are used in the evaluation of many diagnostic exams for sensitivity, specificity, positive and negative predictive values....
Article
Retrospective study
Retrospective studies are cohort or case-control studies that analyze existing data from before the time point at which the study began. These studies are more susceptible to bias and confounding than prospective studies.
Article
Magnetic particle imaging
Magnetic particle imaging (MPI) is an emerging cross-sectional imaging technique that in the future may be a new clinical imaging modality offering high resolution, dynamic functional imaging without utilizing ionizing radiation.
Physics
Magnetic particle imaging is a tracer imaging technique...
Article
Diagnostic test accuracy
The accuracy of a diagnostic test is defined as how often the test correctly classifies someone as having or not having the disease. The formula for accuracy is:
(true positive + true negative) / (true positive + true negative + false positive + false negative)
or correct results / all results...
Article
Alpha vs beta error
Clinical trials may have incorrect results due to random error or bias. The 2 types of random error are called alpha (α) and beta (β), also known as type I and type II errors respectively. Alpha and beta errors are both conditional probabilities. For Radiologists, it may be helpful to think of α...
Article
Hypothesis testing
Hypothesis testing is a statistical method used to evaluate clinical trial results and consists of four consecutive steps:
specification of the null hypothesis and the alternative hypothesis
data collection
statistics and p-value calculation
rejection or failure to reject the null hypothesis...
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