Statistics How To

Design of Experiments > Face Validity What is Face Validity? Face validity, also called logical validity, is a simple form of validity where you apply a superficial and subjective assessment of whether or not your study or test measures what it is supposed to measure. You can think of it as being similar to “face … Read more

Design of Experiments > Case Studies What are Case Studies? Case studies are in-depth studies of a phenomenon, like a person, group, or situation. The phenomenon is studied in detail, cases are analyzed and solutions or interpretations are presented. It can provide a deeper understanding of a complex topic or assist a person in gaining … Read more

Statistics Definitions > Q-Value You may want to read these articles first: What is a False Discovery Rate? What is a P-Value? What is a Q-Value? A Q-value is a p-value that has been adjusted for the False Discovery Rate(FDR). The False Discovery Rate is the proportion of false positives you can expect to get … Read more

Post Hoc Tests > You may want to read this article first: What is the Studentized Range? Newman-Keuls (sometimes called Student–Newman–Keuls or SNK) is a post hoc test for differences in means. Once an ANOVA has given a statistically significant result, you can run a Newman-Keuls to see which specific pairs of means are different. … Read more

Regression Analysis > Residual Plot What is a Residual Plot? Watch the video for an overview and several residual plot examples: Can’t see the video? Click here to watch it on YouTube. A residual value is a measure of how much a regression line vertically misses a data point. Regression lines are the best fit … Read more

Statistics Definitions > Heteroscedasticity The word “heteroscedasticity” comes from the Greek, and quite literally means data with a different (hetero) dispersion (skedasis). In simple terms, heteroscedasticity is any set of data that isn’t homoscedastic. More technically, it refers to data with unequal variability (scatter) across a set of second, predictor variables. Why do we care … Read more

Statistics Definitions > Population Density Human Population Density Population density is a statistic that tells you how many people live in a certain area. In general, pop. density is reported in square miles or kilometers, and may or may not include bodies of water. This type of measurement is called arithmetic density, and is reported … Read more

Sampling > Sampling Variability What is sampling variability? Sampling variability is how much an estimate varies between samples. “Variability” is another name for range; Variability between samples indicates the range of values differs between samples. Sampling variability is often written in terms of a statistic. The variance (σ2) and standard deviation (σ) are common measures … Read more

Statistics Definitions > Content Validity What is Content Validity? Content validity (also called logical or rational validity) refers to the extent to which a test or assessment instrument evaluates all aspects of a behavior, construct, or topic it is designed to measure. In other words, we’re asking if the test fully covers the subject matter: … Read more

Statistics Definitions > What is a Rate Ratio? A rate ratio (sometimes called an incidence density ratio) is a measure of association that compares the incidence of events happening at different times. It is used extensively in epidemiology. The formula is the ratio of exposed groups to unexposed groups: Rate ratio = IRe / IRu … Read more