So far, we’ve been working with one variable. We used z-tests to see if a value of a certain variable (e.g., a value of 6’1” from the variable “height”) differed significantly from the mean value for that variable. We used t-tests to do the same thing, but using samples to approximate populations. And we used ANOVA to look at values of the same variable, but in different groups.

In this lesson, we’ll analyze the relationship between two variables from the same sample (e.g., height and weight, which come from the same people; population and amount of pollution, which come from the same cities; number of students and number of teachers, which come from the same schools). In statistics, this relationship is called the correlation.

Mathematician Hans Rosling has a great video where he visualizes relationships between variables in cool new ways.

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