Welcome back. You've now covered all the essential components of how to fit, assess, and interpret a linear regression model. We've used several different examples examining the outcomes lung function, quality of life, and walking distance. With these outcomes you've learned how to include categorical and continuous predictors and their interactions. After fitting a model, you've learned how you can assess the assumptions made. So, you now have a good grounding in the technical side of model fitting. In the final part of this course we're going to turn our attention to modeling. What I mean by that is a process by which we build our model and select the variables to include. You may have had the preconception that the model building would be a systematic and objective process. But if I gave 10 researchers 10 replicate datasets I think the chances of them coming up with the same model will be extremely low. There are automated methods available for variable selection, but these vary. So even when using automated methods, the results will differ depending on which one you use. This is why we need to be in charge of the modeling process and not some algorithm. So, here's a list of four of variables from the COP dataset. I want you to pick the one that interests you the most. Your challenge is going to be to develop a multiple regression model to determine which variables are associated to the outcome that you've selected. I said at the start of this course, that how a model is developed, will depend on the purpose of the model. So, the model can be used to evaluate a particular intervention or exposure or to understand more about a disease or it can be used for prediction in a clinical setting to either assist in prognosis or diagnosis of patients. The purpose of your model will be to learn about which variables are influencing the outcome. So, I'd like you to develop a model to assess the association of all the variables on the outcome, which fits into the understanding the cause category for purposes of model building. Before you start on this challenge, I'm going to give you some model building tips and suggestions. So, there's a vast literature on this topic and there's a lack of consensus in the research community about the best approach. But there are some approaches that are still frequently implemented that are known to be bad practice. So, I'm going to highlight these for you so you can avoid them. I'm also going to provide you some guidance on how to develop a model building strategy and what components are useful to include in this. The most important thing to do is to ensure you actually have a model building strategy before you start. Otherwise, the process can end up rather ad hoc and it's also good practice to be able to report this strategy when you write up your results. While researchers may not agree on the best approach, at least it's clear what was done on why this was decided. In the next lecture, you'll learn more about automated methods for variable selection and the limitation of using these approaches and then we'll move on to strategies for model building. So see you soon.