Correlation between variables has which key characteristic?

The key characteristic of correlation is that it makes no assumptions about causation. Correlation measures the degree to which two variables move in relation to one another, but it does not imply that changes in one variable cause changes in another. This distinction is crucial in research, as assuming causation without proper evidence can lead to misconceptions about the relationship between variables. For instance, two variables may show a strong correlation due to a third variable influencing both, or they may simply be related by chance.

The other options suggest incorrect assumptions about the nature of correlation. While correlation can apply to linear relationships, it can also apply to non-linear relationships; however, the correlation coefficient itself is specifically designed to quantify linear relationships. Correlation does not require categorical variables; indeed, it often involves continuous variables. Thus, the essence of correlation lies in its ability to describe a relationship without inferring direct cause-and-effect conclusions.