What is used to assess the magnitude and direction of a relationship?

The correct choice is correlation because it specifically measures both the strength (magnitude) and direction of a relationship between two variables. When correlation is calculated, it results in a coefficient that ranges from -1 to +1. A coefficient close to 1 indicates a strong positive relationship, while one close to -1 indicates a strong negative relationship. A coefficient of 0 suggests no relationship at all.

In contrast, the mean is a measure of central tendency that summarizes a dataset with a single value, representing the average. It does not provide any information about relationships between variables.

Standard deviation measures the amount of variation or dispersion in a set of values. While it is important in understanding the distribution of data, it does not indicate any relationship between variables.

Variance is similar to standard deviation in that it also assesses the spread of a set of data points. It quantifies how much the numbers in a dataset differ from the mean but does not assess relationships between two different variables.

Overall, correlation is the only option that directly evaluates the connection between two variables in terms of both size and direction.