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The study of morbidity1 deals with the investigation of illness2, sickness2, ill-health2 or disease2 in a population. Statistics of disease are referred to as morbidity statistics3 or sickness statistics3. As the distinction between health and illness is not sharply defined, it is not always easy to determine the number of cases of disease4 accurately. Health statistics5 cover all aspects of the health of a population, and are generally taken to include statistics of cause mortality6, i. e., mortality classified by cause of death7. As a number of diseases may be causes of death, a combined classification of illness and cause of death is frequently used.
- 1. morbidity n., morbid adj.
- 2. sickness n., — sick adj. — illness n., — ill adj. — disease n., — diseased adj.
The study of cause mortality (420-6) —short for mortality by cause of death— is made difficult because in many cases there may not be a single cause of death1 but multiple causes of death2 or joint causes of death2. When this is the case we may distinguish between the immediate cause of death3 and the underlying cause of death4 or, looking at the problem from a different point of view, we may distinguish between the primary cause of death5 or principal cause of death5 and the secondary cause of death6, contributory cause of death6 or associated cause of death6. The cause mortality rate7 or cause-specific mortality rate7 is generally expressed per 100,000 population. The ratio of the number of deaths from a specific cause to the number of deaths from all causes is sometimes referred to as the death ratio8, or proportionate mortality8.
Death or disability (425-6) may be the consequence of disease (420-2) or of injury1 or poisoning2. Injuries may be due to accident3 or violence4. Among cases of violence we distinguish suicides5 and attempted suicides5, homicides6 and deaths or injuries due to operations of war7.
- 3. accident n. — accidental adj., hence accidental death, also known as death from misadventure.
- 4. violence n. — violent adj.
- 6. homicide n. may in law be murder or manslaughter.
Infectious diseases1 or communicable diseases1 have attracted particular attention, because they are capable of infecting large numbers of persons within relatively short time intervals. In such instances we speak of epidemics2, and special epidemiological statistics3 are collected to show their incidence. It is possible to obtain information about these illnesses because legislation in various countries has made many of them reportable; they are therefore called notifiable diseases4. A distinction is sometimes made between chronic diseases5 and acute diseases6. These terms are not precisely defined, but acute diseases are generally understood to be those of abrupt onset and short duration whilst chronic diseases are those with slow onset and long duration, and often causing prolonged disability.
- 1. infectious adj. — infect v. — infection n.
- 2. epidemic n., also used as adj. — epidemiology, the science dealing with epidemics, epidemiologist, a specialist in epidemiology, — epidemiological adj., appertaining to epidemiology.
Among causes of death which are of particular interest to the demographer, we may mention congenital malformation1, diseases of the newborn2 and diseases connected with pregnancy, labour and the puerperium3 (603-6) or lying-in period3 immediately before or after delivery (603-4*). Mortality from these latter diseases is called maternal mortality4 or puerperal mortality4. If maternal mortality rates are computed with the total population as a base they are cause mortality rates (421-7), if they are related to the total number of births (or more accurately of pregnancies) they are analogous to fatality rates (425-7). The proportion of deaths due to senility5 or to ill-defined causes may be taken as an index to the quality of the system of statistics of causes of death.
- 3. puerperium n. — puerperal adj.
- 5. senility n. — senile adj.
Three aspects of morbidity (420-1) are commonly measured by morbidity rates1 or morbidity ratios1: frequency, duration and severity. Two indices of the frequency of ill-health are the incidence rate2, the number of new cases of disease related to the average population at a particular period of time, and the prevalence rate3, which is the number of cases of ill-health existing at a given moment of time expressed per unit of the average population. The average duration per case4 or the disability rate5, which is the average number of days of disability6 per person, may serve as a measure of the duration of illness. The case fatality rate7, which is the proportion of fatal cases among the reported cases of the specified disease, may be used as an index of severity. It is usually computed only for acute diseases of relatively short duration.
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