Optimal ratio for data splitting

It is common to split a dataset into training and testing sets before fitting a statistical or machine learning model. However, there is no clear guidance on how much data should be used for training and testing. In this article, we show that the optimal training/testing splitting ratio is p:1$$ \sqrt{p}:1 $$ , where p$$ p $$ is the number of parameters in a linear regression model that explains the data well.