Kamus Demografi Pelbagai Bahasa, Edisi Kedua, Volum Bahasa Malaysia

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130

Istilah statistik penduduk¹ atau statistik demografi¹ adalah merujuk kepada data berangka² mengenai penduduk, yang berdasarkan kepada pemerhatian³. Selepas pemerhatian dikumpulkan⁴ pada bentuk-bentuk (206-1) yang bersesuaian, dokumen tersebut akan disunting⁵ dan disahkan⁵ untuk menghilang ketidakseragaman yang jelas. Data tersebut akan ditaburkan⁶ kepada kumpulan-kumpulan⁷ atau kelas-kelas⁸ tertentu yang mempunyai ciri-ciri yang sama. Pemprosesan data⁹ mengandungi kesemua langkah-langkah daripada pengumpulan sehingga analisis statistik¹⁰ (132-1).

131

Data kebiasaannya dirujuk sebagai data mentah¹ atau data kasar¹ sebelum pemprosesan dan taburan dan data asas¹ atau data primer¹ selepas pemprosesan dan taburan. Data asas kebiasaannya mengandungi siri-siri² bagi nombor-nombor mutlak³ yang diletakkan bersama dalam bentuk jadual-jadual statistik⁴. Dalam jadual-jadual tersebut, data umumnya diklasifikasikan mengikut pembolehubah-pembolehubah⁵ or variat-variat⁵ tertentu seperti umur, bilangan anak dan sebagainya, atau mengikut atribut-atribut⁶ atau ciri-ciri⁶ tertentu (sebagai contoh. jantina, status perkahwinan dan sebagainya). Apabila data diklasifikasikan mengikut beberapa pembolehubah atau atribut secara serentak, jadual tersebut dipanggil taburan silang⁷ atau jadual kontingensi⁷. Jadual ringkasan⁸ memberikan maklumat yang kurang lengkap berbanding jadual individu⁹ .

132

Penggunaan data asas umumnya melibatkan dua fasa. Analisis¹ bertujuan untuk mengasingkan komponen-komponen bagi nombor-nombor yang diperhatikan (saiz, struktur, faktor luaran dan fenomena yang dikaji); sintesis² adalah proses menggabungkan semula komponen-komponen yang telah diasingkan dalam pelbagai cara. Sama ada fasa yang melibatkan pengiraan³ atau penghitungan³ bagi indeks⁴ yang boleh diwakili oleh pelbagai nama (cf. § 133). Berbeza dengan data asas, indeks ini dirujuk sebagai hasil⁶ atau indeks sintetik⁵. Dalam erti kata yang lebih khusus, indeks⁷ (pl. indeks atau nombor indeks⁷ adalah nisbah yang menunjukkan nilai bagi kuantiti tertentu terhadap asas⁸, yang kebiasaannya diambil sebagai 100. Beberapa indeks adalah indikator⁹ yang baik bagi sesuatu situasi yang kompleks; maka kadar mortaliti bayi kadangkala digunakan sebagai indikator bagi tahap kesihatan penduduk.

133

One of the first stages of analysis (132-1) consists of relating the population totals or number of events to other totals or numbers. The resulting indices are given various names. A Templat:NewTextTerm, also used for various purposes, is the quotient obtained by dividing quantities of the same kind. When the dividend and divisor belong to the same kind but different categories (men and women, children and women, different age-groups, for example) an other terminology might be used in non English languages, relating both quantities with a specific ratio¹ (like a sex ratio). A proportion² is a ratio which indicates the relation in magnitude of a part to the whole. A percentage³ is a proportion expressed per hundred. A rate⁴ is a special type of ratio used to indicate the relative frequency⁵ of the occurrence of a particular event within a population or a sub-population in a specified period of time, usually one year. Although this usage is recommended, the term has steadily acquired a wider meaning and is often incorrectly used as a synonym for ratio (e.g. labor force participation rate, which is actually a proportion).

134

The relative frequency (133-5) of a non-renewable event is often regarded as an empirical measure of the probability¹ of occurrence of that event. This presumes that all the individuals who appear in the denominator have been exposed to risk³ in some way, i.e. there must have been a chance² or risk² that the event in question could happen to them. The use of the term "risk" does not imply that the event in question is in any way unwanted; thus the term "risk of marriage" is used. The population is often divided into different sub-groups, in which the risk of the event in question is less variable between individuals than in the population as a whole; the subgroup is more homogeneous⁴ with respect to the risk than the relatively heterogeneous⁵ whole population. Rates calculated for such subgroups are called specific rates⁶ as opposed to crude rates (136-8) which apply to the population as a whole. General rates⁷ sometimes involve an age restriction, as in the instance of general fertility rates (633-7).

135

Age-specific rates¹ are computed for single years of age or for age groups (Templat:NewTextTerm or Templat:NewTextTerm). Duration-specific rates³ take into account the time elapsed since a baseline event⁴ or event-origin⁴ such as marriage or a previous birth. Central rates¹⁰ are obtained by dividing the number of events during a year, or some other period (often five years) either by the average population⁶ or mid-year population⁶ or by the number of person-years⁷ of exposure to the event in question during that year or period; the number of person-years is the sum, expressed in years, of the exposure time for all individuals in the observed group, over the year or period. The term rate is often used also for another type of measure, obtained by dividing the number of non-renewable events in a year or a period of years by the size of the cohort considered at the beginning of the year or period; this peasure is sometimes called an attrition probability⁵ or more simply a probability⁵, and contrasted with the central rate, defined earlier. In this paragraph, the word "period" has referred to a length of time. In the expression period rates⁸, however, the word is used in its chronological meaning and refers to a specific calendar year or group of years; it is opposed to cohort rate⁹ or generation rate⁹.

136

Data are called provisional¹ if they are based on incomplete or insufficiently controlled observations. They are replaced by final² data when the observations are complete. Rates based on such data are called provisional rates³ and final rates⁴ respectively. Where information becomes available after figures have already been published, revised rates⁵ may be issued. The expression corrected rate⁶ usually implies that defective data or inappropriate methods have yielded results which are either misleading or of limited value for the purpose in hand and that an effort has been made to correct this, e.g., correction for underenumeration, correction for migration, correction for seasonal movement. Standardized rates⁷ or adjusted rates⁷ are designed to make it possible to compare different populations with respect to a variable, e.g. fertility or mortality, where the influence of another variable e.g. age, is held constant. The term corrected rate⁷ has been used by some demographers as a synonym for standardized rate. When the data do not permit direct estimation of the rates (small population, for example), the use of Templat:NewTextTerm (cf. 403-6 for example) computed from data of good quality and applied to the real population, provides an indirect estimation of the expected number of events which can be compared with the observed number of events. Unstandardized rates are called crude rates⁸. Although they may be used to measure actual trends, false inferences may result from their uncritical use when populations with different structures (144-4) are compared.

137

Demographic indices (132-7) will in most cases relate to a particular period of observation¹ ; this is true in particular of most rates (cf. 133-4). An annual rate² will relate to a period of twelve months. Where observations are collected for a number of years and then averaged, the term mean annual rate³ or average annual rate³ is often used for the result. Where rates are calculated for periods different from a year they are converted to an annual basis⁴ through multiplication by an appropriate factor. Instantaneous rates⁵ are sometimes computed; they relate to an infinitesimal period of time, cf. for instance the instantaneous death rate (431-4) or the instantaneous rate of population growth (702-5).

138

The primary objective of cohort analysis (103-4) is the study of the intensity¹ and tempo² or timing² of demographic phenomena. The intensity of a phenomenon initiated by one non-renewable event (201-4) may be measured by either the ultimate frequency³ of occurrence for the given event or by its complement. The ultimate frequency reflects the proportion of persons who would have experienced the event, in the absence of extraneous influences, during the existence of the cohort (116-2). The intensity of a phenomenon initiated by a renewable event (201-5) such as births or migratory moves, can be measured by the mean number of events⁴ per person in the cohort, also in the absence of extraneous influences. Tempo or timing may be defined as the distribution over time within the cohort of the demographic events corresponding to the investigated phenomenon. The results of cross-sectional analysis or period analysis (103-5) are summarized by period measures⁵ — as opposed to cohort measures⁶ — which can be constructed in various fashions. A commonly used technique consists in attributing the observed rates pertaining to various ages or durations to a hypothetical cohort⁷ or synthetic cohort⁷ .