| Chapter 2: | Background and Theoretical Development |
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Measures of Fertility Decline
An enormous amount of the research literature has used differing measures to examine fertility. All these measures reflect different aspects of the fertility situation of the region examined. These measures are discussed in detail below, and some other measures are used to capture the mechanisms involved in fertility decline in a given region. One of the major indicators used in fertility analysis is the total fertility rate (TFR). TFR is defined as the average number of children born to a woman during her reproductive period, usually defined as comprising ages 15 through 49. This measure is considered a period measure of fertility, because it represents a cross-section of the population at one specific time. A huge volume of the available literature has used TFR as an indicator to measure fertility (Bogue & Palmore, 1964; Bongaarts & Greenhalgh, 1985; Golini, 1998; Retherford, Choe, Chen, Xiu, & Hongyan, 2005; Ryder, 1990; Sanderson, 1979). Another indicator commonly seen in the fertility literature is children ever born, the actual number of children ever born to a woman (Billari, Manfredi, & Valentini, 2000; Gaisie, 1969; Gubhaju, Choe, Retherford, & Thapa, 1987; Knodel, 1978; Myburg, 1956). The introduction of the concept of birth interval (i.e., the duration between the consecutive births of children) was a major breakthrough in the measurement of fertility (Pandey & Suchindran, 1997; Potter, 1963; Sheps & Menken, 1973; Srinivasan, 1966). One of the major advantages of birth interval measures over other measures is that it is relatively more sensitive to capture small changes in the fertility levels and insensitive to factors that are not pertinent to fertility change in a population (Srinivasan, 1966). Two major types of birth intervals are used to study fertility: (a) open birth intervals and (b) closed birth intervals. Open birth intervals are defined as the