Statistics How To

Statistics Definitions > Propensity Score Matching What is a Propensity Score? A propensity score is the probability that a unit with certain characteristics will be assigned to the treatment group (as opposed to the control group). The scores can be used to reduce or eliminate nbpMatching package for R. The psmatch function in STATA can … Read more

Randomized Clinical Trial > Bipartite matching Matching places participants in observational studies into comparable, homogeneous groups or strata at the beginning of a study. It is one way to avoid selection bias (Cochran and Chambers, 1965). Matching designs can be bipartite matching, or non-bipartite matching, which are terms borrowed from graph theory. Bipartite Matching Bipartite … Read more

Statistics Definitions > Treatment-As-Usual What is “Treatment-As-Usual”? Treatment-As-Usual (TAU) means that the usual treatment — according to accepted standards for your particular discipline — is given to a group of participants. For example, psychiatric TAU might include psychotherapy, medication, or a combination of the two (Blais et. al, 2013). In clinical trials, TAU is given … Read more

Hypothesis Testing > Sequential Probability Ratio Test You may want to read these articles first: What is Sequential Sampling? What is a Likelihood-Ratio Test (LRT)? What is a Sequential Probability Ratio Test? A sequential probability ratio test (SPRT) is a hypothesis test for sequential samples. Sequential sampling works in a very non-traditional way; instead of … Read more

Sampling > Sequential Sampling What is Sequential Sampling? In sequential sampling, a sequence of one or more samples is taken from a group. Once the group has been sampled, a hypothesis test is performed to see if you can reach a conclusion. If you can’t, the whole procedure is repeated. A characteristic feature of sequential … Read more

Statistics Definitions > Multiple imputation (MI) is a way to deal with nonresponse bias — missing research data that happens when people fail to respond to a survey. The technique allows you to analyze incomplete data with regular data analysis tools like a t-test or ANOVA. Impute means to “fill in.” With singular imputation methods, … Read more

Probability Distributions > U-Shaped Distribution U-Shaped Distribution A U-Shaped distribution is a bimodal distribution with frequencies that steadily fall and then steadily rise. There is a higher chance of a measurement being found at the extremes than in the center of the distribution. Cyclical and sinusoidal measurements are usually in distributed in U-shapes (Bucher, 2012). … Read more

Hypothesis Testing > Levels in Statistics Levels in Statistics: Contents Levels of independent variables (factors), Confidence Levels, Alpha and Beta levels, Levels of Measurement. 1. Levels of Independent Variables (Factors) A level in factor analysis, or a level of an independent variable, means that the variables can be split up into separate parts. For example, … Read more

Regression Analysis > Multinomial Logistic Regression What is Multinomial Logistic Regression? Multinomial logistic regression is used when you have a categorical dependent variable with two or more unordered levels (i.e. two or more discrete outcomes). It is practically identical to logistic regression, except that you have multiple possible outcomes instead of just one. For example, … Read more

Sampling > Discrepant Case Sampling What is Discrepant Case Sampling? Discrepant case sampling is a sampling method that aims to elaborate, modify, or refine a theory (LeCompte & Preissle, 1993). The goal is to deliberately choose cases that might help to modify an emerging theory, not completely refute it. It is generally used in the … Read more