Statistics Definitions > > Clustered Standard Errors You may want to read this article first: What is the Standard Error of a Sample? What are Clustered Standard Errors? Clustered Standard Errors(CSEs) happen when some observations in a data set are related to each other. This correlation occurs when an individual trait, like ability or socioeconomic … Read more
Time Series > Unit Root What is “Unit Root”? A unit root (also called a unit root process or a difference stationary process) is a stochastic trend in a time series, sometimes called a “random walk with drift”; If a time series has a unit root, it shows a systematic pattern that is unpredictable. The … Read more
Statistics Definitions > Statistical Relationship What is a Statistical Relationship? Relationships in probability and statistics can generally be one of three things: deterministic, random, or statistical. A statistical relationship is a mixture of deterministic and random relationships. A deterministic relationship involves an exact relationship between two variables. For example, let’s say you earn $10 per … Read more
Statistics Definitions > Guttman’s lambda-2 What is Guttman’s lambda-2? Guttman’s lambda-2 (Guttman’s λ2) is a reliability estimate. λ-2 is the second in a series of 6 lambda’s proposed by Guttman in 1945. Lambda-1 was intended as a starting point for reliability analysis. From the 6 lambdas, lambda-2 and lambda-3 (which is equivalent to Cronbach’s alpha) … Read more
Statistics Definitions > Reliability and Validity Contents: Overview What is Reliability? The Reliability Coefficient What is Validity? Curricular Validity Overview of Reliability and Validity Outside of statistical research, reliability and validity are used interchangeably. For research and testing, there are subtle differences. Reliability implies consistency: if you take the ACT five times, you should get … Read more
Statistics Definitions > Durbin Watson Test & Coefficient What is The Durbin Watson Test? The Durbin Watson Test is a measure of autocorrelation (also called serial correlation) in residuals from regression analysis. Autocorrelation is the similarity of a time series over successive time intervals. It can lead to underestimates of the standard error and can … Read more
Statistics Definitions > Contents: Stationarity Differencing 1. What is Stationarity? A time series has stationarity if a shift in time doesn’t cause a change in the shape of the distribution. Basic properties of the distribution like the mean , variance and covariance are constant over time. Types of Stationary Models can show different types of … Read more
Matrices and Matrix Algebra Contents (click to skip to that section): Matrix Algebra: an Introduction Matrix Addition: More Examples Matrix Multiplication Definition of a Singular Matrix The Identity Matrix What is an Inverse Matrix? Eigenvalues and Eigenvectors Augmented Matrices Determinant of a Matrix Diagonal Matrix What is a Symmetric and Skew Symmetric Matrix? What is … Read more
Regression Analysis > Stepwise Regression Stepwise regression is a way to build a model by adding or removing predictor variables, usually via a series of F-tests or T-tests. The variables to be added or removed are chosen based on the test statistics of the estimated coefficients. While the technique does have its benefits, it requires … Read more
Statistics Definitions > Variance Inflation Factor You may want to read this article first: What is Multicollinearity? What is a Variance Inflation Factor? A variance inflation factor(VIF) detects multicollinearity in regression analysis. Multicollinearity is when there’s correlation between predictors (i.e. independent variables) in a model; its presence can adversely affect your regression results. The VIF … Read more