Appearance of Ossification Centers

The appearance of ossification centers roughly follows a standard time schedule. But irregularities in the time and order of appearance of centers are common enough to make assessment of "skeletal age" by the Todd¹or Flory²atlases in many cases difficult if not impossible. It was felt that these variations could be better understood if one could demonstrate that there are groups of ossification centers and that it is these groups which show more or less independence in their times of appearance. For instance, if one center of a certain group were retarded, all other centers of that group should also tend to be retarded. Do such groups exist? This can best be answered statistically. A "group" implies mutual relations among variables. It was therefore decided to intercorrelate the ages at which the ossification centers appear. A group of apparently normal, healthy white children is being observed at