6io THE POPULAR SCIENCE MONTHLY. 



avoided. Physicians have taken considerable interest in censuses, 

 and for the very reasons stated, and so in many cases health dis- 

 tricts have been prescribed and the statistics of population and 

 the social facts relating to population for such health districts 

 preserved. In this way the very best results are to be reached. 

 With complete statistics of population for clearly defined health 

 districts, where the sanitary conditions can be compared and 

 differences of conditions noted, a scientific study of death-rates 

 with reference to the density of population can be undertaken. 

 The ordinary statistics of death-rates based on the density of 

 population of cities are exceedingly vicious, but perhaps not 

 more so than the ordinary statements relative to the death-rate 

 of cities based on the whole population. There is great liability 

 to very misleading statistics in this direction. The errors arise 

 from two causes. The first of these is the incompleteness of death 

 statistics. This can only be overcome by a compulsory registra- 

 tion of deaths. The second cause is that population is not accu- 

 rately known except for periods some distance apart, and here 

 error arises, and would arise, even with complete and perfect 

 statistics of deaths ; as, for instance, a State which depends 

 entirely upon the Federal census ascertains its population only 

 once in ten years. For the census year the death-rate based on 

 population may be fairly accurate ; but for intermediate years 

 the death-rate must be based upon calculations of population 

 mathematically made. In some cases this has led to very vicious 

 results, and has caused considerable fright and anxiety on account 

 of the great apparent death-rate, when, had the facts all been 

 known, it would have been found that the death-rate was really 

 normal. Another feature of error, or rather feature for the basis 

 of erroneous conclusions, relative to the death-rate in great cities, 

 arises from the fact of the existence of large hospitals in cities, 

 and that the death-rate is increased by people coming from the 

 country to the cities for treatment and there passing awa}^ thus 

 giving an abnormally high death-rate relative to the actual living 

 population of a city. This is also true in connection with the 

 criminal statistics of cities. Men come in from country towns for 

 the purpose of a visit or a spree, or for carrying out some nefari- 

 ous design. At all events, they commit crime, from one cause or 

 another, within the city limits, are there arrested and punished^ 

 and their crimes help to swell abnormally the legitimate criminal 

 statistics of the city itself. All these considerations should be 

 taken into account when writers are undertaking to draw what 

 they feel to be accurate conclusions through comparisons of sta- 

 tistics. I have read very learned essays upon conditions of the 

 population, involving insanity, crime, disease, death, etc., when 

 all the conclusions of the essays were based upon most incomplete 



