The proportional or percentage rate of increase of any economic variable over a unit period, usually a year. If a variable measured over discrete time intervals grows from 1 to 1 + x, this is a proportional growth rate of x, or a percentage growth rate of 100x. If working in continuous time, a continuous constant growth rate g means that a variable grows from 1 at time 0 to e^gt at time t. If y_t = y₀e^gt, dy_t/dt = gy₀e^gt, and (dy_t/dt)/y_t = g. As ln(y_t) = ln (y₀) + gt, d ln (y_t)/dt = g; the rate of change of the natural logarithm of any variable equals its growth rate. See also natural growth rate; warranted growth rate.