Function, often applied to growth curves, fitting the general equation \[y = k/(1 + e^{a+bt})\] where \(t\) represents time, \(y\) the body weight or population size, \(k\) the rate of growth, and \(a\) and \(b \gt 0\) are constants. In the logistic equation the percentage rate of increase decreases linearly as size increases. The resulting curve continually rises, slowly at first, more rapidly in the middle phase, and slowly again near the end of growth.