Statistics How To

Statistics Definitions > A data distribution is a function or a listing which shows all the possible values (or intervals) of the data. It also (and this is important) tells you how often each value occurs. Often, the data in a distribution will be ordered from smallest to largest, and graphs and charts allow you … Read more

Statistics Definitions > What are Absolute Dispersion and Relative Dispersion? Absolute & relative dispersion are two different ways to measure the spread of a data set. They are used extensively in biological statistics, as biological phenomena almost always show some variation and spread. The easiest way to differentiate relative dispersion/absolute dispersion is to check whether … Read more

Statistics Definitions > Parameter Estimation is a branch of statistics that involves using sample data to estimate the parameters of a distribution. Methods of Parameter Estimation The techniques used for parameter estimation are called estimators. Some estimators are: Probability Plotting: A method of finding parameter values where the data is plotted on special plotting paper … Read more

Statistics Definitions > The difference in differences (DiD) method is a statistical technique or quasi-experimental design method, and it is used primarily in the social sciences and econometrics. In social science it is sometimes called a “controlled before-and-after” study. General Method The basic DiD method involves comparing results from two groups, with data from each … Read more

Validity > Incremental validity refers to the additional benefit a particular predictor variable has above other predictors. Incremental Validity in Practice An example of incremental validity: Let’s say a medical practitioner is more likely to correctly diagnose a kidney infection if a urine test is ordered, rather than relying on a physical examination and discussion … Read more

Variance > “Shared variance” can mean several things, depending on what field you’re in. In statistics, shared variance generally refers to covariance. However, the term is sometimes used in textbooks as part of the formal definition for the correlation coefficient (shared variance divided by combined variance).

Basic Statistics > Significant Digits Significant digits refers to how many important or interesting digits there are in a number. For example: 221 = 3 sig. digits 2212 = 4 sig. digits 2211.1 = 5 sig. digits 0.0022 = 2 sig. digits. We aren’t ever interested in leading zeros.

Propensity Score Matching > Genetic matching is an algorithm that iteratively checks propensity scores. It improves them using a combination of propensity score matching and Mahalanobis distance matching (Diamond & Sekhon, 2012). The jury is out on whether genetic matching is a “better” method than any of the other matching techniques. Genetic matching may theoretically … Read more

PCA > A Burt table is the necessary input for Multiple correspondence analysis. The Burt table is the symmetric matrix of every two-way cross-tabs between categorical variables; it is analogous to covariance matrix of continuous variables.

Z Scores > A raw score is simply unaltered data from a test or observation. It is recorded in its original form by a researcher before being subjected to any statistical analysis. For instance, if a participant is given a set of ten questions and answers seven right, their raw score might be 7. Typically … Read more