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A fundamental statistical unit1 used in demography is the individual2 or person2 (the term head2 (cf. 221-6) has also been employed, but this usage is now largely out of date). The household3 is a socio-economic unit, consisting of individuals who live together. Statistical definitions of the household vary. According to the definition which has been recommended as an international standard a household consists of a group of individuals who share living quarters and their principal meals. The term hearth3 has been used in the past, showing that in the past members of the household used to share the same fire. Classifications of households also vary between different countries and different enquiries. In order to facilitate comparative studies the internationally recommended classification involves the distinction of two types: private households4 or family households4 and institutional households5 or non-family households5 which consist of people living in certain institutions. An individual living by himself is considered to be a one-person household6 for statistical purposes. A boarder7 is a person other than a domestic servant, who is unrelated to other members of the household and who habitually takes his meals with the household. A lodger8, on the other hand, does not habitually take his meals with the household. These two categories may or may not be included in the household for statistical purposes.
- 8. lodger n. — in the United States of America this term is used to include both boarders and lodgers as defined above.
When a private household (110-4) contains several persons they are called members of the household1 and one of them will be the head of the household2. There is no universally accepted rule as to who is considered the head of the household —in some cases it may be the principal earner3. On some census schedules there appears a question dealing with the relationship4 (114-3*) of members of the household to its head; this enables a distinction to be made between different groups in composite households5, which contain members of more than one biological family (113-1).
- 2. The term householder is sometimes used for the head of the household.
The family1 (cf. 115-1) is a different unit which must be carefully distinguished from the household (110-3). It is defined primarily by reference to relationships which pertain to or arise from reproductive processes and which are regulated by law or by custom. The fundamental relationships are those established between a couple by marriage—and that existing between a couple as parents2, i. e., father3 and mother4, and their children5 i. e., sons6 and daughters7.
- 2. parent n. — parental adj. — parenthood n., the state of being or becoming a parent. Note that the term "parent", when used in the singular is not equivalent to the French "parent".
- 3. father n. — paternal adj.
- 4. mother n. — maternal adj.
- 6. son n. — filial adj.
- 7. daughter n. — filial adj.
Parents and their children are sometimes referred to as the biological family1. Brothers2 and sisters3, without distinction of sex, are called sibs4 or siblings4. Siblings with only one parent in common are called half-brothers5 or half-sisters6.
Persons related through common descent1 from the same progenitor2 or ancestor2 are called blood relatives3 or genetic relatives3. The term kin3 is also used. The degree of relationship4 is generally computed by reference to the number of steps which are necessary before a common ancestor is reached, but there are many different methods of computation. The fundamental relation in each of these steps is the filial relation5 (112-6* and 112-7*) of child to parent, which is the reciprocal of parenthood6(112-2*) i. e., the relation of a couple or of a father or mother to offspring7or progeny7. Blood relationship must be distinguished from affinal relationship8 or relationship by marriage8, which marriage establishes between one spouse and the kin of the other.
- 1. descent n. — descendant n., one linked through descent.
- 2. ancestor n. — ancestral adj.
- 3. relative n. — related adj. — relationship n., the state of being related.
The term relative in ordinary language is used for both blood and affinal relatives. kin n. and adj. — relative, related — sometimes also used for the collection of all kin — kinship n., the state of being kin.
- 7. progeny n. — this term may also be used for all the descendants of a common ancestor.
The family1 (cf. 112-1) as a unit in demographic studies needs to be specifically defined and definitions for different purposes may vary. A unit so selected may be called a census family1 or a statistical family1. In some countries the definition of a statistical family may approximate to the biological family, in others the definition may be based on the nuclear family2 or family nucleus2 consisting of the head of the household, his spouse and their unmarried children. These may either form the census family itself or be the core of such a family.
- 1. In the United States of America the primary family is that family unit which contains the head of the household; a sub-family is a married couple with or without children, or a parent with one or more children under 18 years of age, living in a household and related to, but not including the head of the household and his wife. In Great Britain the primary family unit consists of parents and their children, the parents’ sibs and ancestors. A broken family is one in which one of the parents has been lost by death, divorce or desertion; and there is also the abnormal family, such as an unmarried mother and her illegitimate children. The joint family or composite family generally consists of more than two generations of a biological family and is found in countries where it is not the custom for children to leave the parental home on marriage.
In non-technical language the term "generation" is often used loosely to refer to persons of similar age at the same time. In technical literature, the term generation1 has been given a precise meaning and refers to a group of persons born within a specified period of time, generally taken as a calendar year. More recently the term cohort2 has been introduced to denote a group of persons who experience a certain event in a specified period of time: thus a birth cohort is a synonym for generation in the sense of 116-1, a marriage cohort is a group of persons married within a defined period etc. The term generation2 may also be used as a synonym for cohort, e. g. a marriage generation. In demography as in genealogy the term generation3 may also be used to denote the descendants of a group of persons who are themselves a generation, in the sense of 116-1. Thus children of a group of migrants are often referred to as the second generation. Sometimes consideration is restricted to lines of descent through one sex only, thus a male generation4, or paternal generation4 are the sons of a generation of males, a female generation5 or maternal generation5 the daughters of a generation of females. These distinctions are used particularly when the length of a generation or the mean interval between successive generations (713-1) are computed.
- 2. cohort n. — the term cohort analysis has been used to denote a method of analysing data, in which the experience of individual cohorts is studied throughout their lives, or other specified periods.
For purposes of military service the number of men who become liable to conscription in a given year is sometimes called the class (cf. 130-8) of that year. In the United States the same term is used for a group who complete their studies at a particular school or university in a particular year.
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