Lecture 9

Up until now we have discussed how to interpret and evaluate whether a fitted model is `good’. However before making use of a fitted model through interpretation, it is wise to check that it provides an adequate description of the data. The formula that we have derived enables us to fit a regression model to data, however, if we have not examined the model fit to the data to make sure that the model and techniques we have used are appropriate then we may find at a later stage that we have reached invalid conclusions. In this section we will consider some general methods for checking regression models. All of them are informal and based on graphical methods.