 Predicting the exact volume of gelato to be consumed in Rome next summer is more difficult than predicting that more gelato will be consumed next summer than next winter. For although it is a foregone conclusion that higher temperatures beget higher demand for gelato, the precise relationship between daily temperatures in Rome and consumo di gelato is far from certain. Modeling quantitative, predictive relationships between random variables, such as the relationship between the temperature in Rome, X, and volume of Roman gelato consumption, Y, is the subject of regression analysis.