Statistics How To

Bias in Statistics > Information Bias What is Information Bias? Information bias (also called observation bias or measurement bias) happens when key information is either measured, collected, or interpreted inaccurately. According to John’s Hopkins, it’s when: “…information is collected differently between two groups, leading to an error in the conclusion of the association.” This broad … Read more

Inter-rater Reliability > Fleiss’ Kappa What is Fleiss’ Kappa? Fleiss’ Kappa is a way to measure agreement between three or more raters. It is recommended when you have Likert scale data or other closed-ended, ordinal scale or nominal scale (categorical) data. Like most correlation coefficients, Kappa ranges from 0 to 1, where: 0 is no … Read more

Statistics Definitions > Generalized Mean / Power Mean What is the Generalized Mean? The generalized mean (also known as the power mean or Hölder mean) is just a way of expressing most of the common means (like the arithmetic mean) in one formula: If you change λ (you’ll see this as p in some forms … Read more

Hypothesis Testing > Multiple Testing Problem What is the Multiple Testing Problem? If you run a hypothesis test, there’s a small chance (usually about 5%) that you’ll get a bogus significant result. If you run thousands of tests, then the number of false alarms increases dramatically. For example, let’s say you run 10,000 separate hypothesis … Read more

Sampling > Maximum Variation Sampling What is Maximum Variation Sampling? Maximum variation sampling is what the name implies: a sample is made up of extremes. or is chosen to ensure a wide variety of participants. Samples collected are typically small (from 3 up to about 50). Above 50 items, quota sampling or a similar non-probability … 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 > Eta Squared / Partial Eta Squared What is Eta Squared? Eta squared is the proportion of variance associated with one or more main effects, errors or interactions in ANOVA. Calculation The formula is: Eta2 = SSeffect / SStotal, where: SSeffect is the sums of squares for the effect you are studying. SStotal … Read more

Design of Experiments > Main Effect What is a Main Effect? A main effect (also called a simple effect) is the effect of one independent variable on the dependent variable. It ignores the effects of any other independent variables (Krantz, 2019). In general, there is one main effect for each independent variable. For example, let’s … Read more

Effect Size > What is Epsilon Squared? In statistics, epsilon squared is a measure of effect size (Kelly, 1935). It is one of the least common measures of effect sizes: omega squared and eta squared are used more frequently. Epsilon Squared Formula The formula is basically the same as that for omega squared, except that … Read more

Correlation Coefficients > Phi Coefficient What is the Phi Coefficient? The Phi Coefficient is a measure of association between two binary variables (i.e. living/dead, black/white, success/failure). It is also called the Yule phi or Mean Square Contingency Coefficient and is used for contingency tables when: At least one variable is a nominal variable. Both variables … Read more