Glossary

The sequence in which children are born to a woman. The first child has a birth order of 1, the second is 2, and so on.

A period-based measure, formalized in this paper, representing the average number of live births a mother would have if current age-specific fertility rates remained constant throughout her reproductive years (ages 15–49), providing granular insight into family size.

The various factors and processes that influence birth rates and fertility patterns over time, including socioeconomic, cultural, and biological factors.

The difference between the number of children that people desire to have and the number they achieve [39].

A proposed subdiscipline that captures fertility dynamics below the macro level. While traditionally tied to microdata studies, this paper broadens the term to include all sub-macro approaches—such as the Microdemographic Framework (MDF)—that reveal disaggregated fertility patterns [22].

Traditionally cited as a Total Fertility Rate (TFR) of approximately 2·1 children per woman, this is an estimate of the number of children needed to maintain a stable population, assuming no migration effects and stable mortality rates. It accounts for child survival rates, which vary by region, so the exact figure is not always 2·1 [63].

A period-based indicator introduced in this paper to quantify how far a country’s current fertility rate deviates from replacement level (typically 2·1). An RLI of 0.0% indicates exact replacement. Negative values reflect the percentage shortfall relative to replacement fertility and help contextualize the pace of generational decline.

A period-based indicator estimating the number of years required for a country’s annual births to decline by half—and by successive halves—if current fertility rates persist. Introduced in this paper, SHL offers a concise measure of the pace of demographic contraction and complements conventional fertility indicators such as TFR and RLI.

The period-based incidence of childlessness within a population, measured at the societal level (e.g., annually) using metrics like the Total Childlessness Rate (TCR). It reflects the proportion of women who, during a given period, have not had children, regardless of biological, voluntary, or circumstantial factors. This measure captures emergent demographic trends and distinguishes population-wide fertility patterns from individual or cohort-based childlessness.

Demographic period metrics that summarize the behavior or characteristics of an entire society during a specific period, such as a year. Unlike cohort or cross-sectional measures, these metrics, like TFR, TMR, TCR, and CPM, aggregate data across different groups to provide a snapshot of societal trends during that period.

A period-based demographic measure, defined as the complement of the Total Maternal Rate (TMR). It represents the proportion of women who would remain childless if current age-specific first-birth rates were to remain constant throughout their reproductive years (ages 15–49, for example). Formally,
TCR = 1 – TMR.

A standard period-based measure of the average number of children a woman would have if current age-specific fertility rates remained constant throughout her reproductive years (ages 15–49, for example) [7].

A period-based measure of the proportion of women who would become mothers if current age-specific first-birth rates remained constant throughout their reproductive years (ages 15–49, for example). It is equivalent to the Parity Progression Ratio (PPR) 0→1 whenever this is expressed as a period measure. This paper formalizes TMR to improve accessibility and clarity in demographic analysis.

When individuals or couples remain childless without intentionally avoiding parenthood, often due to socioeconomic constraints, lack of a partner, or limited fertility awareness, within their reproductive years. This differs from involuntary childlessness in which individuals or couples are unable to conceive or carry a pregnancy to term despite attempting to do so, most often due to underlying biological or medical causes, such as infertility or recurrent miscarriage. The term is increasingly used in public discourse in this context and was formally adopted in the 57-nation OSCE Porto Declaration on the Demographic Crisis in 2025 [57].