Statistics How To

Post Hoc Tests > Scheffe Test What is the Scheffe Test? The Scheffe Test (also called Scheffe’s procedure or Scheffe’s method) is a post-hoc test used in Analysis of Variance. It is named for the American statistician Henry Scheffe. After you have run ANOVA and got a significant F-statistic (i.e. you have rejected the null … Read more

Bias > Aggregation Bias & Ecological Fallacy Definition In ecological studies, aggregation bias happens when a researcher incorrectly assumes that trends in aggregated data also apply to individual data points. When data is aggregated, or merged, it can hide trends that are happening between individual variables. It is the expected difference between effects for the group … Read more

Bias > Availability Bias / Availability Error Definition The term “availability bias” has two distinct meanings, depending on where you’re using it: In assessement and decision making, it refers to readily available memories. In meta-analysis, it is used as a synonym for publication bias. 1. Use in Assessement and Decision Making Availability Bias (also called … Read more

Design of Experiments > Prospective study What is a Prospective Study? A prospective study (sometimes called a prospective cohort study) is a type of cohort study, or group study, where participants are enrolled into the study before they develop the disease or outcome in question. The opposite is a retrospective study, where researchers enroll people … Read more

Internal Consistency > Split-Half Reliability What is Split-Half Reliability? In split-half reliability, a test for a single knowledge area is split into two parts and then both parts given to one group of students at the same time. The scores from both parts of the test are correlated. A reliable test will have high correlation, … Read more

Reliability and Validity > Parallel Forms Reliability What is Parallel Forms Reliability? Parallel forms reliability (also called equivalent forms reliability) uses one set of questions divided into two equivalent sets (“forms”), where both sets contain questions that measure the same construct, knowledge or skill. The two sets of questions are given to the same sample … Read more

Bias > Acquiescence Bias What is Acquiescence Bias? Acquiescence bias is the tendency for people to agree rather than disagree. This happens when a question is posed with unbalanced answers like agree/disagree or yes/no. It is a common form of measurement error in surveys and when it happens, it has substantial effects. Acquiescence bias isn’t … Read more

Statistics Definitions > Cochran’s Q Test What is Cochran’s Q Test? Cochran’s Q Test is a non parametric way to find differences in matched sets of three or more frequencies or proportions. It is an extension of the McNemar test; the two tests are equal if Cochran’s Q is calculated for two groups. The test … Read more

Bias in Statistics > Central Tendency Bias What is Central Tendency Bias? Central tendency bias (sometimes called central tendency error) is a tendency for a rater to place most items in the middle of a rating scale. For example, on a 10 point scale, a manager might place most of his employees in the middle … Read more

Statistics Definitions > Test-Retest Reliability / Repeatability Test-Retest Reliability Test-Retest Reliability (sometimes called retest reliability) measures test consistency — the reliability of a test measured over time. In other words, give the same test twice to the same people at different times to see if the scores are the same. For example, test on a … Read more