Categorized or continuous? Strength of an association - and linear regression

Key points • Correlation and regression are used with continuous variables • Plot the variables in correlation and regression relationships to aid interpretation • An association between two discrete measurements is assessed by correlation • Regression describes and quantifies a relationship between an independent factor and a dependent variable; prediction is also possible • Few biological relationships are truly linear • Regression can be distorted by outlying values • Absence of a linear regression does not mean a relationship is not present • Regression is very frequently misused and mis-applied