Statistics How To

Design of Experiments > Predictive Validity What is Predictive Validity? A research study is useless unless it has some kind of predictive value. Predictive validity tells you how well a certain measure can predict future behavior. One of the most common uses for predictive validity is in University Admissions. Grade Point Average, SAT/ACT scores and … Read more

Purposive Sampling > Expert Sampling What is Expert Sampling? Expert sampling (or judgment sampling) is where you draw your sample from experts in the field you’re studying. It’s used when you need the opinions or assessment of people with a high degree of knowledge about the study area. When used in this way, expert sampling … Read more

Sampling > Critical Case Sampling What is Critical Case Sampling? Critical case sampling is where you collect samples that are most likely to give you the information you’re looking for; They are particularly important cases or ones that highlight vital information. This type of sampling is “…particularly useful if a small number of cases can … Read more

Sampling > Extreme Case Sampling What is Extreme Case Sampling? Extreme Case Sampling focuses on participants with unique or special characteristics. An extreme case (or deviant case) can be thought of as an outlier —an observation that takes on an extremely high or extremely low value. The general idea is that if you study extremes … Read more

Sampling > What is Typical Case Sampling> Typical Case Sampling allows you to develop a profile about what is usual or average for a particular phenomenon. For example, let’s say you were studying violence in schools. The first step would be to list all of the criteria that define violence for a “typical” school. Then … Read more

Probability Distributions > Multinomial Distribution The multinomial distribution is used to find probabilities in experiments where there are more than two outcomes. Binomial vs. Multinomial Experiments The first type of experiment introduced in elementary statistics is usually the binomial experiment, which has the following properties: Fixed number of n trials. Each trial is an independent … Read more

Types of Variable > Extraneous Variable What are Extraneous Variables? Extraneous variables are any variables that you are not intentionally studying in your experiment or test. When you run an experiment, you’re looking to see if one variable (the independent variable) has an effect on another variable (the dependent variable). In an ideal world you’d … Read more

Statistics Definitions > The Pareto Principle Contents (Click to Skip to That Section): What is the Pareto Principle? Applying the 80/20 Rule to Your Life The Pareto Principle in Business Pareto Analysis and The Pareto Diagram The Pareto Principle and My Jeopardy Challenge Other Names for the Pareto Principle What is the Pareto Principle? Simply … Read more

ANOVA > Within-Group Variation What is Within-Group Variation? Within-group variation (sometimes called error group or error variance) is a term used in ANOVA tests. It refers to variations caused by differences within individual groups (or levels). In other words, not all the values within each group (e.g. means) are the same. These are differences not … Read more

Statistics Definitions > What is a Geometric Distribution? The geometric distribution represents the number of failures before you get a success in a series of Bernoulli trials. PDF for the Geometric Distribution This discrete probability distribution is represented by the probability density function: f(x) = (1 − p)x − 1p For example, you ask people … Read more