Statistics How To

Statistical Process Control > A defect concentration diagram is a visual representation—usually, a diagram or map—which shows all defects or problem areas in what is being analyzed. As a research tool, it may began as a blank diagram or picture, in which problem locations are marked down as they happen or are discovered. It may … Read more

Coefficient of Association > The contingency coefficient is a coefficient of association that tells whether two variables or data sets are independent or dependent of each other. It is also known as Pearson’s Coefficient (not to be confused with Pearson’s Coefficient of Skewness). It is based on the chi-square statistic, and is defined by: In … Read more

Sampling > Double sampling is a two-phase method of sampling for an experiment, research project, or inspection. An initial sampling run is followed by preliminary analysis, after which another sample is taken and more analysis is run. It is used in three main ways: acceptance/rejection double sampling, ratio double sampling, and stratification double sampling. We’ll … Read more

Statistics Definitions > Discrete choice models are used, primarily in economics, to model the choices made between well-defined alternatives. Typically they model the choices a consumer might make between a finite set of alternate products or services. The set of all alternatives available is called the choice set. If there are just two alternatives, it … Read more

Statistics Definitions > The uncertainty coefficient, also called the entropy coefficient, or proficiency, is a measure of the entropy (that is, uncertainty) in a column variable Y which a row variable X explains. It is sometimes expressed in symbols as or U(X|Y) or U(C|R), where C is columns and R is rows. Disambiguation Note: Theil … Read more

Design of Experiments > Flexible design is a form of design which allows for interim feedback that may change the course of a trial or experiment. It’s sometimes used synonymously with adaptive design. However, there is a subtle difference: The term “adaptive design” refers to specific design types (e.g. adaptive allocation or sample size re-assessment), … Read more

Regression Analysis > What is the Levenberg–Marquardt Algorithm? The Levenberg–Marquardt (LM) Algorithm is used to solve nonlinear least squares problems. This curve-fitting method is a combination of two other methods: the gradient descent and the Gauss-Newton. Both the Gradient Descent and Gauss-Newton methods are iterative algorithms, which means they use a series of calculations (based … Read more

Probability > A probability vector is a vector (i.e. a matrix with a single column or row) where all the entries are non-negative and add up to exactly one. It’s sometimes also called a stochastic vector. As a simple example, the vector (1/6, 1/6, 1/6, 1/6, 1/6, 1/6) represents the probability distribution of a random … Read more

Statistics Definitions > What is a Coefficient of Association? A Coefficient of Association measures the strength of a relationship. “Association” means that the variables have shared or common elements or some degree of agreement. A large number of different association coefficients is available. Which you choose is dependent on many factors, including the data type … Read more

Descriptive Statistics > Waterfall Plot The term “waterfall plot” is used to refer to several very different types of graphs and charts in different disciplines. In many fields, a waterfall plot is considered to refer to a three-dimensional graph where spectral data is arranged as a function of noise or speed. These waterfall plots look … Read more