Given the straightforward assumptions on how the factors of production evolve over time, the steady-state level of output per capita can be expressed as a function of the propensity to accumulate physical and human capital, the population growth rate, the level and growth rates of technological and economic efficiency, and the (constant) rate of depreciation of capital. If countries were at their steady state - or if deviations from the steady state were random - growth equations could be based simply on the relationship linking steady-state output to its determinants. However, actual data may well include out-of-steady-state dynamics due, among other things, to slow convergence towards the steady state.