Theory of statistical regularity that a normal distribution occurs over time as the average of data observed tends to be distributed evenly under general conditions . Its hypothesis is that no matter how a variable changes, the sum of its values will show a normal distribution if enough measurements are taken. Formulated by the Russian mathematician Alexander Mikhailovich Lyapunov (1857-1918), he drew upon the work of the French mathematician PierreSimon Laplace (1749-1827). It forms the basis of the law of large numbers where Its usefulness lies in its complete generality.