# Psychometrics from the Ground Up 10: Covariance

In this tutorial I discuss and present visual representations of covariance. Although covariance is not directly informative, it is a fundamental ingredient in almost all of the most frequently used statistical procedures.

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# Psychometrics from the Ground Up 9: Standard Scores and Why We Need Them

In this video tutorial, I explain why we have standard scores, why there are so many different kinds of standard scores, and how to convert between any two types of standard scores.

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# Psychometrics from the Ground Up 8: Kurtosis (Beyond Peakedness)

In this video tutorial, I show why the typical description of kurtosis is not quite right and, in some cases, quite wrong.

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# Psychometrics from the Ground Up 7: Skewness (Lopsided Variability)

A video tutorial in which I explain what skewness is, how it arises, and various ways it can be conceptualized.

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# Psychometrics from the Ground Up: 6. The Normal Distribution and the Central Limit Theorem

A video tutorial about why many variables have a normal distribution:

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# Psychometrics from the Ground Up: 5. Expected Value and Variance

A video tutorial about Expected Value and its relationship with variance:

## Topics Covered:

• Some Rules of Expected Value Computations
• Measuring Variability Using Expected Values
• The Relationship between the Normal Distribution and the Chi Square Distribution
• Raw Moments
• Central Moments
• The 2nd Central Moment (i.e., Variance) in Terms of Raw Moments
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# Psychometrics from the Ground Up: 4. Expected Value (What Does the Mean Mean?)

A video tutorial about a different of thinking about the meaning of the mean:

In this video, we take a simple question and we make it complicated so that we can make some complicated questions simple.

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# Psychometrics from the Ground Up: 3. Probability Density Functions

A video tutorial about probability density functions. They are like histograms on steroids!

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