What does correlation measure?

Correlation measures the strength and direction of a relationship between two variables, which is why the chosen answer is correct. It quantifies how closely related the two variables are, indicating whether they tend to increase or decrease together (a positive correlation) or if one increases while the other decreases (a negative correlation). The correlation coefficient, which can range from -1 to +1, provides a numerical value for this relationship, with values closer to -1 or +1 indicating a stronger relationship and a value of 0 indicating no correlation.

The other options pertain to different statistical concepts. Causation, described in the first option, refers to a cause and effect relationship, which correlation does not measure; correlation only indicates a relationship, not causation. The third option refers to comparing differences between groups, which is typically assessed through other statistical methods, such as t-tests or ANOVAs. The final option about outcomes of an experiment is relevant to experimental research rather than correlation, which applies to observational data where variables are not manipulated.