Whenever a continuous-valued predictor variable is included in an analysis, it is assumed there is a linear relationship between the response and predictor variables, i.e., the expected value of the response variable consistently increases (or decreases) as the value of the covariate increases. There will be many situations where this is unreasonable, particularly in ecological situations. In this video Darryl provides some tips on things an analyst needs to consider when analysing their data.
