How to Use a Z-Table (Standard Normal Table)

In this video I explain how to use a z-table or a standard normal table in order to calculate the percentage of scores below, above, or between z-scores for a normal distribution. Finding the areas under the curve associated with … 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

What is Kurtosis?

In this video I explain the concept of kurtosis. I explain the terminology for kurtosis coined by Karl Pearson, a number of common misconceptions related to kurtosis, how kurtosis is calculated for a sample, and how kurtosis is interpreted for … Read More

How to Calculate Skew

In this video I explain two formulas for calculating skew: Pearson’s Median Skewness or Pearson’s 2nd equation for skew, and the Adjusted Fisher-Pearson Standardized 3rd Moment Coefficient for skew. I also explain some general guidelines for interpreting skew values, as … 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

Skewness – Positive & Negative Skew

In this video I explain one way in which a distribution can deviate from normality, which is skewness. I explain the difference between positive and negative skew, and how these can be seen in histograms, stem and leaf displays, and … Read More

Histograms & Frequency Polygons

In this video I explain the difference between histograms and bar charts, look at the creation of histograms and frequency polygons for continuous variables, and then discuss why we want to get a sense of the shape of a distribution … Read More

Exploratory Data Analysis: Box & Whisker Plots

In this video I describe box-and-whisker plots, or boxplots, developed by John Tukey. First we’ll look at a simple box-and-whisker plot, then we’ll see some variations depending on the data, some different sets of terminology that can be used when … Read More

Exploratory Data Analysis: Stem & Leaf Displays

In this video I explain stem-and-leaf displays or stemplots, which are part of exploratory data analysis developed by John W. Tukey. I explain the basic design of stem-and-leaf displays as well as several variations including back-to-back stem-and-leaf displays and stretched … Read More