These rates are not corrected for age distribution or nationality or for any other factors or many of these differences would disappear. The low proportion of individuals over 40 and the excessive proportion of children are responsible for the low rates from the diseases of old age and the high rates from the communicable diseases of childhood, while the Italian susceptibility to respiratory diseases and relative resistance to tuberculosis explains the marked differences in these rates.

The crude death rate per 1,000 population for the Health Center for the six-year period is 14.7, compared with 16.3 for the city and 15.6 for the State. Correction for age distribution on the basis of the population of New Haven increases the Health Center rate to about 15.4 and leaves the city rate unchanged at 16.3. The State rate has not been corrected.

Although abundant reasons are given below why little or no value can be attached to any comparison either in the number of deaths, in death rates or in percentage reductions, between the Health Center district and the remainder of the city, the following table is presented, which shows the percentage reductions in the mortality of residents of all ages of the two districts in 1921 and in 1922 as compared with a six-year average, 1915-20, and a five-year average, eliminating 1918, the year of the influenza epidemic . A similar table, dealing with infant mortality, is to be found on page 92.

From this table it may be observed that the percentage reduction in resident deaths in 1921, when based upon the preceding 6 year period was identical in the two districts under comparison, while slightly greater (1.0%) in the remainder of the city when based upon the preceding 5 year period, eliminating 1918.

For the year 1922 the greater reductions are to be found in the Health Center district, 15.0% and 8.3% as compared with the 11.8% and 5.9% respectively, for the two preceding periods. When the increase in mortality in 1922 is compared with the mortality in 1921 it is found that the remainder of the city increased 4.27% more than the Health Center district.

The following pages will point out, it is hoped, some of the reasons why such comparisons as those just made cannot be regarded as significant.

1. Population

A comparison, year by year, of the mortality in the Health Center district with that in the remainder of the city, in order to be valid, must take many factors into consideration. The assumption is frequently made in such comparisons that these factors are operating in equal degree in the two contiguous groups and therefore may be disregarded. Such factors as the changes in the size, nationality, age and sex of the two groups, the completeness of birth registration and the accuracy of death certification may, on the other hand, be acting in unequal magnitude in the two groups and if this is the case care must be exercised in making comparisons.

A study of the available information suggests that in one respect, namely, the size of the population, changes are taking place from year to year in the Health Center district, which make mortality comparisons with the remainder of the city dangerous, whether the comparisons be in terms of percentage reductions of the actual mortality in subsequent years or mortality rates.

The Health Center information regarding the population of tile three wards comprising it have been obtained from two sources, the U. S. Censuses of 1910 and 1920 and the three censuses of the district made by our sanitary inspector.

The following data are presented:

The facts of particular interest in these figures are:

1. The increase of only 1,400 in 10 years. While we do not possess data regarding Health Center births prior to 1918 or Health Center deaths prior to 1915, it is reasonable to assume that the average excess of births over deaths for 1918-20 represents a conservative average for the 1910-20 period. This average yearly excess of births over deaths is 591, or 5,910 for the ten years. The difference between 1,400 and some such figure as 5,910 must be accounted for either through an understatement of the 1920 census, which seems most unlikely in view of the subsequent Health Center census, or through emigration from the district. The latter alternative is accepted, though we have been unable to obtain any direct evidence to substantiate it.

2. The close agreement of the sanitary inspector's house-to-house census early in 1921 with the U.S. Census of January 1, 1920, a difference of only 1.5%.

3. The marked decrease in the census enumeration of the sanitary inspector in the spring of 1922, there being 1,857 less people than recorded in his 1921 1U. S. Census. This census was performed more carefully than the preceding, the name and age of every individual being obtained in addition to many other items. No house or apartment was knowingly missed. There were, however, 470 unrented apartments and 20 undergoing repairs. Unfortunately the 1921 census did not record the number of unrented apartments, but the inspector believes they were few in number. If the 490 apartments had been occupied by the average of 4.5 occupants there would have been 2,205 more individuals in the district. There were also fewer boarders, 1,294 in 1922 as compared with 1,592 in 1921. This decrease in population, which we would not have been able to estimate had the census not been made is to be explained, we believe, by the serious period of unemployment which closed, for a time, practically all the factories in the district and resulted in the disappearance of a number of inhabitants.

Obviously, the number of deaths occurring among 24,426 people would not be the same as that which would occur among 26,840 and the comparisons of the percentage reductions of 1922 deaths as compared with the 1915-20 deaths of the Health Center and the remainder of the city would be invalid. For example, on the basis of the 1921 death rate (11.0 per 1,000) a population of 2,271 would represent 25 deaths, and a reduction of 25 deaths on a basis of 295 deaths (in 1921) would represent 8.5%.

Since it is impossible to know how the population for the remainder of the city has been affected during 1921, 1922 and 1923, it is futile for this reason, if not for the several reasons discussed below, to attempt to compare the total mortality of the two districts either on the basis of actual deaths or of death rates calculated from population estimates.

Other factors affecting the validity of any comparison of mortality in the two districts which have been considered are the following: age distribution, birth rates, treatment of non-resident deaths, treatment of deaths in hospitals and other institutions .. and treatment of deaths of residents in State institutions outside New Haven. In order that some of the pitfalls encountered in attempting a comparison of mortality may be more fully understood, these above factors will be discussed separately.

2. Age Distribution

A glance at the following table will reveal that the Health Center has a great preponderance of children and a paucity of the aged. With the exception of the first two years of life, the Health Center has an age distribution particularly favorable to a low mortality. If the Health Center had the same proportion of infants under one as the remainder of the city it would have 537 infants instead of 813.

It happens that the age distribution of New Haven is so similar to the age distribution of the registration area that its crude death rate is unchanged when so standardized. The Health Center crude death rate, when standardized on the age distribution of New Haven, is increased from 11.0 to 11.8 for 1921, and from 12.2 to 12.6 for 1922.

3. Birth Rate

The Health Center has a markedly higher birth rate than the remainder of the city. The tendency of a high birth rate to be associated with a high infant mortality suggests that the Health Center's high birth rate may affect its infant mortality adversely. The striking differences are shown in the following table: