Statistics How To

Types of Bias What is Neyman Bias? Neyman Bias is a selection bias where the very sick or very well (or both) are erroneously excluded from a study. The bias (“error”) in your results can be skewed in two directions: Excluding patients who have died will make conditions look less severe. Excluding patients who have … Read more

Types of Variables > What is an Attribute Variable? The term “attribute variable” can refer to either an input variable used in statistical software or a manipulated variable used in design of experiments. 1. Usage in Software Some statistical software packages (like Statistica and Minitab) use “attribute variable” as an alternate name for categorical variables. … Read more

Bias in Statistics > What is Diagnostic Bias? Diagnostic bias (sometimes called diagnostic suspicion bias or provider bias) is when your perceptions color your diagnosis. This type of bias can happen when knowledge of an exposure is used as a diagnostic criterion. It can also happen because personal biases, like prejudice or subjective judgment affect … Read more

RCTs > What is Attributable Risk? Attributable Risk(AR) (sometimes called Attributable Proportion or Attributable Fraction) is a measure of the prevalence of a condition or disease. Given a group of people exposed to a risk, it’s the fraction who develop a disease or condition. Put another way, AR is the cases that would be eliminated … Read more

Statistics Definitions > Gold Standard Test What is a Gold standard Test? A gold standard test is a best available diagnostic test for determining whether a patient does or does not have a disease or condition. For example, a biopsy can identify breast cancer cells with good accuracy, while an autopsy are usually accurate at … Read more

Bias > What is Referral Bias? Referral bias (also called admission rate bias) is a specific type of

Measures of Association > What is Somers’ Delta? Somers’ Delta (Somers’ D) is a measure of agreement between pairs of ordinal variables. Ordinal variables are ordered , like best to worst or smallest to greatest (the Likert scale is one of the more popular ordinal scales.) A measure of agreement tells you something about how … Read more

Statistics Definitions > Classical Test Theory What is Classical Test Theory? Classical Test Theory (CTT), sometimes called the true score model, is the mathematics behind creating and answering tests and measurement scales. The goal of CTT is to improve tests, particularly the reliability and validity of tests. Reliability implies consistency: if you take the ACT … Read more

Types of Bias > What is Verification Bias? Verification bias (also called detection bias or workup bias) is the selective use of a single “gold standard” diagnostic test in a study. Some patients are given the “gold standard” verification test, while others are not; The reason for this is that many gold standard tests are … Read more

Probability distributions > Empirical Distribution Function Definition An empirical cumulative distribution function (also called the empirical distribution function, ECDF, or just EDF) and a cumulative distribution function are basically the same thing: they are both probability models for data. However, while a CDF is a hypothetical model of a distribution, the ECDF models empirical (i.e. … Read more