Statistics How To

Hypothesis Tests > The Chi-Square Test for Normality allows us to check whether or not a model or theory follows an approximately normal distribution. The Chi-Square Test for Normality is not as powerful as other more specific tests (like Lilliefors). Still, it is useful and quick way of for checking normality especially when you have … Read more

Statistics Definitions > A trimean is a number that represents the general tendency of a set of numbers or data set. Like the mean, median, and mode, it is a measure of central tendency. It is defined to be the weighted average of the median and upper and lower quartiles. As a formula: Trimean = … Read more

Types of Variable > A ranked variable is an ordinal variable; a variable where every data point can be put in order (1st, 2nd, 3rd, etc.). You may not know an exact value of any of your points, but you know which comes after the other. Examples of Ranked Variables Suppose you ran a satisfaction … Read more

Regression Analysis > Relative Weights What are Relative Weights? Johnson’s Relative Weights is a way quantify the relative importance of correlated predictor variables in regression analysis. “Relative importance” in this context means the proportion of the variance in y accounted for by xj. Put another way, it helps you figure out what variables contribute the … Read more

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

Sampling > What is Inverse Sampling? In inverse sampling (sometimes called standard inverse sampling), you continue to choose items until an event has occurred a specified number of times. It is often used when you don’t know the exact size of the sample you want to take. For example, let’s say you were conducting a … Read more

Statistics Definitions > You may want to read this article first: What is a Sufficient Statistic? What is the Rao-Blackwell Theorem? The Rao-Blackwell theorem (sometimes called the Rao–Blackwell–Kolmogorov theorem or Rao-Blackwellization) is a way to improve the efficiency of initial estimators. Estimators are observable random variables used to estimate quantities. For example, the (observable) sample … Read more

Statistics Definitions > Sheppard’s Correction for Grouping Errors are adjustments to calculated sample moments for grouped data (i.e. data that has been binned). The correction is named after W.F. Shepard, who noted than when moments are calculated for continuous frequency distributions, it is assumed that the data is centered around the class interval midpoints. This … Read more

Statistics Definitions > Shifting data is adding a constant k to each member of a data set, where k is a real number. In visual terms, it is lifting the entire distribution of data points and shifting en masse a distance of k. Shifting Data and the Mean & Median When data is shifted the … Read more

Statistics Definitions > Rescaling data is multiplying each member of a data set by a constant term k; that is to say, transforming each number x to f(X), where f(x) = kx, and k and x are both real numbers. Rescaling will change the spread of your data as well as the position of your … Read more