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
Mean Absolute Deviation, Variance, & Standard Deviation
In this video I explain how to use mean deviation, mean absolute deviation, variance, and standard deviation to assess dispersion in interval or ratio level data. I discuss each concept and practice calculating with a sample set of data, and … Read More
How to Use Interquartile Range to Identify Outliers
In this video I explain how to use the interquartile range in order to identify possible outliers in a data set. This can be done using the interquartile range times 1.5 for moderate outliers, or times 3 for extreme outliers. … Read More
Dispersion: Range, Interquartile Range, & Semi-Interquartile Range
In this video I explain simple ways of describing the dispersion of data that can be ordered or ranked. These are the range, the interquartile range, and the semi-interquartile range. I also briefly describe a more precise method for calculating … 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
How to Find the Precise Median (Interpolated Median)
In this video I explain how to find the precise median for a continuous variable with many repeated scores. I walk through an example of this that can be solved visually, then use this example to derive the formula for … Read More
Understanding Central Tendency
In this video I explain the strengths and limitations of the 3 measures of central tendency: the mean, the median, and the mode. This is part of a key theme of statistics, which is the importance of the choices researchers … Read More
Scales of Measurement or Types of Data
In this video I describe the 4 scales of measurement proposed by Stanley Smith Stevens, which have become the standard way of defining types of data. These include nominal, ordinal, interval, and ratio. I discuss the defining features of each, … Read More
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