Statistics How To

Statistics Definitions > Probabilistic What is Probabilistic? A probabilistic method or model is based on the theory of probability or the fact that randomness plays a role in predicting future events. The opposite is deterministic , which is the opposite of random — it tells us something can be predicted exactly, without the added complication … Read more

Statistics Definitions > Resistance and Resistant Measures What is Resistance? Resistant statistics don’t change (or change a tiny amount) when outliers are added to the mix. Resistance doesn’t mean it doesn’t move at all (that would be “immovable” instead). It means there might be a little movement in your results, but not much. When a … Read more

Hypothesis Tests > Granger Causality What is Granger causality? Granger causality is a way to investigate causality between two variables in a time series. The method is a probabilistic account of causality; it uses empirical data sets to find patterns of correlation. Causality is closely related to the idea of cause-and-effect, although it isn’t exactly … Read more

Regression Analysis > Simultaneous Equations Model (SEM) You may want to read this other article first: What is Simultaneity? What is a Simultaneous Equations Model (SEM)? A Simultaneous Equation Model (SEM) is a model in the form of a set of linear simultaneous equations. Where introductory regression analysis introduces models with a single equation (e.g. … Read more

Regression Analysis > Reverse Causality What is Reverse Causality? Reverse causality means that X and Y are associated, but not in the way you would expect. Instead of X causing a change in Y, it is really the other way around: Y is causing changes in X. In epidemiology, it’s when the exposure-disease process is … Read more

Design of Experiments > What is Treatment Diffusion? Treatment diffusion is where the control group is affected by the treatment. This could happen because individuals in the control groups and treatment groups talk to each other about the treatment. As such, this is usually an issue in research involving training or informational programs (Borg, 1984). … Read more

Regression Analysis > Simultaneity Bias What is Simultaneity? Simultaneity is where the explanatory variable is jointly determined with the dependent variable. In other words, X causes Y but Y also causes X. It is one cause of endogeneity (the other two are omitted variables and measurement error). A similar (and often confused) bias is reverse … Read more

Regression Analysis > Instrumental Variable What is an Instrumental Variable? An instrumental variable (sometimes called an “instrument” variable) is a third variable, Z, used in regression analysis when you have endogenous variables—variables that are influenced by other variables in the model. In other words, you use it to account for unexpected behavior between variables. Using … 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 > Jaccard Index What is the Jaccard Index? The Jaccard similarity index (sometimes called the Jaccard similarity coefficient) compares members for two sets to see which members are shared and which are distinct. It’s a measure of similarity for the two sets of data, with a range from 0% to 100%. The higher … Read more