These estimates have been made as at fifteen years of age since the effect of the excessive mortality especially among the isolation group is uncertain and may need to be allowed for in a discussion of the percentage deficient at different ages. If the mortality were as great as has been described among institutional cases in the previous chapter, a rough estimate of the percentage intellectually deficient in the general population places it at less than 0.5%. This estimate may be made by using the estimated deficiency at the median age of those under 15 years of age and at the median age of those 15 years of age and over. According to the age distribution of the 1910 census, there were 32% under 15 years with a median age of 6 years. At age six 0.67% would be presumed as low as 0.50% at 15 years. The older group (68% of the population) has a median age of 32 with a corresponding percentage in the isolation group at that age of 0.30%, after allowing for differences in mortality on the plan indicated in Table II. This rough estimate for the lowest group indicates that 0.42% of the general population would be of as low a degree of intellectual capacity as the lowest 0.5% at 15 years. Our plan presumes, therefore, that between 0.4% and 0.5% of the population are unable to pass their entire lives outside of institutions under ordinary conditions; _i. e._, make an honest living and live within the law even with social assistance and supervision. The corresponding estimate for those requiring only social assistance would be between 0.8% and 1.0% of the general population above the lowest group. This might vary from approximately 1.34% at 6 years to 0.59% at 32, the median age for those over 14 years. Since the mortality is probably less among deficients not in institutions, as they average higher in ability, the changes in the percentages are probably extreme estimates. We should keep in mind, however, the possibility that with the excessive death rate the lowest 1.0% at 15 may mean an ability corresponding to the lowest 1.34% at 6 years and the lowest 0.60% at 32 years.