In statistics, the coefficient of determination, denoted R² or r² and pronounced R squared, is a number that indicates how well data fit a statistical model – sometimes simply a line or a curve. An R² of 1 indicates that the regression line perfectly fits the data, while an R² of 0 indicates that the line does not fit the data at all. This latter can be because the data is more non-linear than the curve allows, or because it is random.