In the 1950s, James Hamilton created a scale with seven stages through which the progressive development of male hair loss became apparent.
Later, the above scale was also revised by O’Tar Norwood.
The resulting scale is known as the Hamilton-Norwood scale or simply Norwood.
As the above scale illustrates the evolutionary course of androgenetic alopecia it becomes apparent that the more advanced the stage the greater the hair loss
It should be clarified at this point that the time duration of the transition from one stage to the next is not fixed, as the rate of dilution can vary greatly from person to person.
Thus, while in some cases the hair loss may occur gradually, in others the indiscernible thinning may last for many years and develop rapidly, leading to the final stages of the above scale in a comparatively short period of time compared to the previous development.