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The study of morbidity 1 deals with the investigation of illness 2, sickness 2, ill-health 2 or disease 2 in a population. Statistics of disease are referred to as morbidity statistics 3 or sickness statistics 3. As the distinction between health and illness is not sharply defined, it is not always easy to determine the number of cases of disease 4 accurately. Health statistics 5 cover all aspects of the health of a population, and are generally taken to include statistics of cause mortality 6, i. e., mortality classified by cause of death 7. 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 death 1 but multiple causes of death 2 or joint causes of death 2. When this is the case we may distinguish between the immediate cause of death 3 and the underlying cause of death 4 or, looking at the problem from a different point of view, we may distinguish between the primary cause of death 5 or principal cause of death 5 and the secondary cause of death 6, contributory cause of death 6 or associated cause of death 6. The cause mortality rate 7 or cause-specific mortality rate 7 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 ratio 8, or proportionate mortality 8.
Death or disability (425-6) may be the consequence of disease (420-2) or of injury 1 or poisoning 2. Injuries may be due to accident 3 or violence 4. Among cases of violence we distinguish suicides 5 and attempted suicides 5, homicides 6 and deaths or injuries due to operations of war 7.
- 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 diseases 1 or communicable diseases 1 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 epidemics 2, and special epidemiological statistics 3 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 diseases 4. A distinction is sometimes made between chronic diseases 5 and acute diseases 6. 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 malformation 1, diseases of the newborn 2 and diseases connected with pregnancy, labour and the puerperium 3 (603-6) or lying-in period 3 immediately before or after delivery (603-4*). Mortality from these latter diseases is called maternal mortality 4 or puerperal mortality 4. 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 senility 5 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 rates 1 or morbidity ratios 1: frequency, duration and severity. Two indices of the frequency of ill-health are the incidence rate 2, the number of new cases of disease related to the average population at a particular period of time, and the prevalence rate 3, 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 case 4 or the disability rate 5, which is the average number of days of disability 6 per person, may serve as a measure of the duration of illness. The case fatality rate 7, 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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