### Cross-validation

In this article, we will be talking about the importance of cross-validation to choose the best model. To do this, we will show:
the problem of using simple in-sample metrics for model selection with a univariate example the problem of using simple in-sample metrics for model selection with a multivariable example how to perform cross-validation using simple linear regression and some problems associated with this 1) The problem of using simple in-sample metrics for model seelction with a univariate example When dealing with a regression model, we are often interested in determining which covariates to keep in the model and which to through away.