Any measure of the link between two variables as shown by quantitative or qualitative data describing their characteristics. Links between continuous variables (e.g. mass and height or crop yield and rainfall) may be assessed statistically using correlation and regression methods. Links between qualitative characteristics (e.g. aspect and slope form) may be assessed statistically using contingency tables and tests based on χ2 or an appropriate non-parametric test. Sometimes continuous variables can be more conveniently tested in qualitative form, e.g. height as short, medium, or tall, especially when the link with some other qualitative variable is wanted, e.g. aspect and tree height.
Subjects: Plant Sciences and Forestry — Ecology and Conservation.