What is a Probability Density Function?

In this video I explain probability density functions and how these are used to describe the distribution of a population and estimate the probabilities for different ranges of scores within that distribution. I also explain why the probability for a … Read More

How Are Moments Used in Statistics?

In this video I explain how moments are used in statistics in order to describe the characteristics of a distribution. The first four moments help to tell us about the mean, variance, skew, and kurtosis of a distribution and allow … Read More

Skewness – Floor & Ceiling Effects

In this video I explain how skewness in a sample may be caused by a floor or a ceiling effect, in which the measurement isn’t able to capture variability at the low or high end of a population’s distribution. A … Read More

How to Interpret (and Create) Frequency Distribution Tables

In this video I explain frequency distribution tables and grouped frequency distribution tables for summarizing data. I explain each of the columns, including the variable measured, the frequency, the proportion and percentage of the data at each variable, and the … Read More

n-1 Explained Conceptually

In this video I answer the common question of why we divide by n-1 when calculating variance from a sample, known as Bessel’s Correction. I focus on conceptual understanding of why this adjustment is needed and why n-1 is the … Read More

Inclusive vs. Exclusive Interquartile Range

In this video I explain the difference between calculating an exclusive interquartile range and an inclusive interquartile range. While we generally use an exclusive interquartile range with an even set of scores, when we have an odd-numbered set of scores … Read More

Dispersion for Nominal Data: The Variation Ratio

In this video I describe how we can describe dispersion or variability in nominal data by calculating a variation ratio. This is a simple measure of spread that tells us the frequency of scores that differ from the mode, which … Read More