Statistics How To

Regression Analysis > Nonlinear Regression What is Nonlinear Regression? Nonlinear regression uses nonlinear regression equations, which take the form: Y = f(X,β) + ε Where: X = a vector of p predictors, β = a vector of k parameters, f(-) = a known regression function, ε = an error term. The formal definition is that … Read more

Extreme Value Distributions > Gumbel Distribution What is the Gumbel Distribution? The Gumbel distribution (also called the Gumbel type) is a popular, asymmetric, extreme value distribution(EVD), used to model maximums and minimums. For example, the EVD Type I has been used to predict earthquakes, floods and other natural disasters, as well as modeling operational risk … Read more

Extreme Value Distribution > Fréchet Distribution What is the Fréchet Distribution? The Fréchet Distribution, also called the extreme value distribution(EVD) Type II, is used to model maximum values in a data set. It is one of four EVDs in common use. The other three are the Gumbel Distribution, the Weibull Distribution and the Generalized Extreme … Read more

Statistics Definitions > Relative Precision What is Relative Precision? “Relative Precision”(RP) is one of those catch all terms that can mean slightly different things depending on where you’re using it. For example, the coefficient of variation is a type of RP used to compare results from two tests or surveys, while in more general terms, … Read more

Correlation Coefficients > Intraclass Correlation Intraclass Correlation Intraclass correlation measures the reliability of ratings or measurements for clusters — data that has been collected as groups or sorted into groups. A related term is interclass correlation, which is usually another name for Pearson correlation (other statistics can be used, like Cohen’s kappa, but this is … Read more

Statistics Definitions > Curvilinear Regression Contents: Curvilinear Regression Curvilinear Regression Curvilinear regression analysis fits curves to data instead of the straight lines you see in linear regression. Technically, it’s a catch all term for any regression that involves a curve. For example, quadratic regression and cubic regression. About the only type that isn’t includes in … Read more

Item Response Theory > Rasch Analysis What is a Rasch Model? The Rasch model is used to measure latent traits like attitude or ability; It shows the probability of an individual getting a correct response on a test item. The Rasch model is a lot simpler and intuitive than many other models. It resembles a … Read more

Sampling > Respondent-Driven Sampling What is Respondent-Driven Sampling? Respondent-driven sampling(RDS) is similar to snowball sampling, a chain-referral sampling method where participants recommend other people they know. Both techniques are useful for sampling from hard-to-reach populations, like IV drug users or sex workers. The main difference between the two is that RDS is mathematically tweaked to … Read more

Correlation Coefficients > Polychoric Correlation What is Polychoric Correlation? Polychoric correlation measures agreement between multiple raters for ordinal variables (sometimes called “ordered-category” data). Ordinal variables can be placed in order, but can’t be divided or multiplied. For example: a person’s level of depression, their level of disagreement or agreement, or how much they value possessions. … Read more

Correlation Coefficients > Point Biserial Correlation Contents: Point Biserial Correlation Biserial Correlation 1. What is Point Biserial Correlation? The point biserial correlation coefficient, rpbi, is a special case of Pearson’s correlation coefficient. It measures the relationship between two variables: One continuous variable (must be ratio scale or interval scale). One naturally binary variable.* Many different … Read more