Descriptive Statistics > A variogram is an effective tool for describing the behavior of non-stationary, spatial random processes. It is used primarily in spatial statistics, geostatistics, and statistical design; In geostatistics, it is an “essential step” for analyzing spatial variability…

## ARMA model

Statistics Definitions > An ARMA model, or Autoregressive Moving Average model, is used to describe weakly stationary stochastic time series in terms of two polynomials. The first of these polynomials is for autoregression, the second for the moving average. Often…

## Allocation Bias: Simple Definition, Examples

Bias > Allocation bias happens when researchers don’t use an appropriate randomization technique, leading to marked, systematic differences between experimental groups and control groups. It can also happen further down the line, if clinical staff don’t follow the procedures set…

## Bradford Distribution / Bradford Law of Scattering

Probability Distributions > The Bradford distribution (also called the Bradford Law of Scattering) is a right-skewed distribution with a peak at the distribution’s minimum. It is a special case of the beta distribution of the second kind or Pearson’s Type…

## Resampling Techniques

Sampling > Resampling techniques are a set of methods to either repeat sampling from a given sample or population, or a way to estimate the precision of a statistic. Although the method sounds daunting, the math involved is relatively simple…

## Lomax Distribution (Pareto II)

Probability Distributions > What is the Lomax Distribution? The Lomax distribution is a heavy tailed distribution originally proposed by Lomax (1987), who used it in his analysis of business failure lifetime data. The distribution, which is basically a shifted Pareto…

## Compound Probability Distribution

Probability Distributions > Compound Probability Distribution What is a Compound Probability Distribution? A compound probability distribution has random variables drawn from a “compound” parametric distribution, where one or more of the distributions parameters (i.e. the mean) are taken from other…

## Upper Tail and Lower Tail: Definition

Statistics Definitions > Upper Tail and Lower Tail What is a “Tail”? The “tails” of a distribution are, just like the name suggests, the appendages on the side of a distribution. Although it can apply to a set of data,…

## Proportional Reduction in Error (PRE Test)

Statistics Definitions > What is the Proportional Reduction in Error (PRE Test)? The Proportional Reduction in Error (PRE Test) is a statistical criterion which quantifies the extent that knowledge about one variable can help us predict another variable. That is…

## Varimax Rotation: Definition

Statistics Definitions > Varimax rotation is an important second step in Factor Analysis and Principal Component Analysis. The initial factor analysis step has an infinite number of initial, or provisional, factors. Factor rotation, including Varimax rotation, transforms the initial factors…