years of adult life it closely approaches a straight line), the number thus found would in each case be 100 per cent. The departures from 100 per cent, therefore, in the following table measure approximately, and the departures from the figures in the first column measure more accurately, the irregularity and probable error in the reported ages in Porto Rico. Columns for the United States and Cuba are introduced for comparison.

Per cent that population in each quinquennial group makes of the arithmetical mean of population in the next younger and next older groups.

By disregarding the first two age groups and finding for each following group the differences between the figures in the first column and those in each other column, one obtains a measure of the real or alleged excess or deficiency of population in certain age periods. Measure of excess (+) or deficiency (−) of population in age group named.

In all three countries the population in age groups including a multiple of 10 was usually in excess, and that in other age groups in deficiency. In Cuba the deviation from the standard after the age of 30 was greater and in most instances many times greater than in the United States, and in Porto Rico with few exceptions it was much greater than in Cuba. In the United States where ages are reported

by single years it can easily be shown that the irregularity of the age curve is due to the reporting of ages as 30, 40, etc., when the persons are near but not at those ages. This tendency is most marked among the uneducated. The preceding table shows that in both of the Spanish West India islands a similar tendency is at work with greater effect than in the United States, and that in Porto Rico it is more influential than in Cuba. Minor differences between the three countries may also be traced in the table. Thus, in both the West India islands, especially in Cuba, there seems to be a depletion of the age period 20 to 24 and a concentration on the following 5-year period, while in the United States the reverse is true. On the other hand, here is a very marked concentration in both islands on the age periods 40 to 44 and 70 to 74 which is lacking in the United States, where there is a curious avoidance of those periods in the reporting of ages.

In a single case this explanation may be further tested. In Table IX the number of persons 20 years of age is given as well as those 21-24. In Farr's Life Table the persons 20 years of age are 20.3 per cent of the total in the group 20-24. In the United States the proportion for both sexes was 20.7, but as males in the United States are fond of saying they are of voting age, and the year 21 is a favored one with them, it may be better to compare the Porto Rican figures for this group with those for females in the United States. Of all females in the United States 20-24, 22.4 per cent reported themselves as 20 years of age. In Porto Rico, on the contrary, of all persons 20-24, 33.6 per cent reported themselves as 20. This confirms the explanation already offered, that the Porto Ricans stated their age in round numbers as some multiple of ten far more commonly than the Americans did in 1890. The per cent of the total population of each department belonging to each quinquennial age period is shown in the following table:

Age period.

Per cent of total population belonging to age period stated.

Aguadilla. Arecibo. Bayamon. Guayama. Humacao. Mayaguez. Ponce.

This table throws some light upon the table already given (p. 47), showing median age by departments. For example, from the former table it appeared that the median age in Mayaguez was more than half a year higher than that of any other department. From the present table it appears that Mayaguez has a smaller proportion of children under 15, and a larger proportion of persons at each age period but one between 30 and 60, than any other department. The median age of the population is closely dependent upon the proportion of children under 15. This appears from the following table, in which the departments are arranged in the order of their median age, and the proportion of children under 15 to the total population is given:

It will be seen that the departments with a low median age are uniformly those with a high proportion of children, while those with a high median age are those in which the proportion of children is smaller.

In the same way, the high median age of the urban population is due to the small proportion of children under 15 found in the cities of Porto Rico. Treating the population of these cities as a unit, it appears that the children under 15 therein constituted only 32 per cent of the total population of the cities, while in the rest of Porto Rico such children constituted 44.9 per cent, a difference between city and country of 12.9 per cent, or thrice that separating the two most diverse departments.

AGE AND SEX.

In Porto Rico the median age of the males is 17.5 years, while that of the females is 18.6 years; that is, the females were more than a year older than the males. In the United States in 1890 the males were four-fifths of a year older and in Cuba in 1899 more than eighteen months older than the females. Each sex in Porto Rico was much younger than the corresponding sex in Cuba or the United States.

The greater age of females is elucidated by the following table. It states the ratio between the total number of each sex in a given quinquennial age group and the total of that sex at all ages.

From the preceding table it appears that in Porto Rico a much larger proportion of the males than of the females are under 15, but that this difference is almost entirely offset by the fact that among females a much greater proportion are between 15 and 30. The higher median age of females is thus due to the disproportionate number of males among children and apparently of females among young adults. After the age of 30 the proportion of the two sexes remains almost the same. It would appear from the table, however, that the proportion of males is greater in the age periods 55 to 59 and 65 to 69, while that of females is greater in the periods 50 to 54, 60 to 64, 70 to 74, and 80 to 84. This difference may plausibly be assigned to the greater inaccuracy with which the ages of Porto Rican women are returned. As already shown, a considerable number belonging outside the period including a multiple of ten have been returned as in these periods, and this tendency affecting women more powerfully than men has distorted in the table the real balance of the sexes during the higher age periods. To determine whether this hypothesis is correct the following table for the two sexes has been constructed in accordance with the method previously explained (p. 50, f.):