### Population projection by sex, age and region

Istat's regional demographic projections are built with the aim of representing the possible future trend of the population, both in terms of total numbers and in terms of age and sex structure.

The information produced represents an important tool to support decisions in economic and social policies, such as those relating to pension, health, education and housing systems.

The projections are periodically updated by reformulating the evolutionary assumptions underlying fertility, survival, international and internal migratory movements.

### Population projection by sex, age and region

**Age specific fertility (rate)**: the ratio of the number of live births to women between the ages of x and x + 1 and the average number of women of that age in a given year.

**Average number of children per woman**: the number of children a woman would have if she was subjected to the fertility calendar (in the form of age-specific fertility rates) of a given calendar year during her reproductive life span.

**Birth (rate)**: ratio between the number of live births in the year and the average amount of the resident population, multiplied by 1,000.

**Cohort component (model)**: the continuous calculation algorithm that in iterative mode simulates the evolution of the fundamental population equation by age group, allowing to determine the demographic flows and to obtain the surviving population at the end of each year.

**Couple**: two people linked by an emotional and sentimental relationship. Can be formed by opposite or same sex people. The bonds between people in couples can be formal (de jure couple: married, civilly united or de facto cohabiting pursuant to law 76/2016) or informal (de facto couple).

**Death**: the cessation of any sign of life at any time after the vital birth.

**Demographic projection**: elaboration that shows the future development of a population when certain assumptions are made regarding the future course of mortality, fertility and migration.

**Deterministic demographic projection**: elaboration on the future development of a population, summarized in a single series of values obtained from a single set of demographic assumptions, which does not report any measure regarding the uncertainty usually associated with the results.

**Dependency ratio**: ratio between the population of inactive age (0-14 years and 65 years and over) and the population of active age (15-64 years), multiplied by 100.

**Elderly dependency ratio**: ratio between the population aged 65 and over and the population aged 15-64, multiplied by 100.

**Emigration for abroad (rate)**: the ratio between the number of emigrations to abroad and the average amount of the resident population, multiplied by 1,000.

**Family households (or households with at least one family nucleus)**: includes couples with children, couples without children, single parents, families with two or more nucleus.

**Non family Households (or households without nuclei)**: people living alone or multi-person families; this latter do not constitute a family unit even if composed of several people.

**Family nucleus**: group of people linked by ties of marriage, kinship, affinity, adoption, protection, or by emotional ties, cohabitants and having habitual residence in the same Municipality. It can also be constituted by a single person.

**Household**: set of people who form a couple or a parent-child relationship. It means a married couple, civilly united or cohabiting, with or without children, or even a single parent together with one or more children who have never been married. Within a household there may be one or more family nucleus, but there may also be none, as in the case of households formed by an isolated member (one-person household) or several isolated members (multipersons household).

**Household typology**: classification based on the presence or absence of at least one nucleus and by type of nucleus.

**Immigration from abroad (rate**): the ratio between the number of immigrations from abroad and the average amount of the resident population, multiplied by 1,000.

**Internal emigration (rate)**: the ratio between the number of internal emigrations and the average amount of the resident population, multiplied by 1,000.

**Internal immigration (rate)**: the ratio between the number of internal immigrations and the average amount of the resident population, multiplied by 1,000.

**Internal migration balance**: difference between the number of registrations for change of residence from another Municipality and the number of de-registrations for change of residence to another Municipality.

**Internal net migration (rate)**: the difference between the internal immigration rate and the internal emigration rate.

**Life expectancy at age "x"**: the average number of years that a person of completed age "x" can count to survive in the hypothesis that, in the course of his subsequent life, he was subjected to the risks of mortality by age (from age "x" up) of the year of observation.

**Life expectancy at birth**: the average number of years that a person can count to live from birth in the hypothesis that, in the course of his existence, he was subjected to mortality risks by age of the year of observation.

**Live birth**: the product of conception which, once expelled or completely extracted from the maternal body, regardless of the duration of gestation, breathes or manifests other signs of life.

**Mean age**: mean age of the population at a certain date expressed in years and tenths of a year.

**Mean age at birth**: the mean age at birth of mothers expressed in years and tenths of a year, calculated considering only live births.

**Migratory balance with abroad**: difference between the number of registrations for change of residence from abroad and the number of de-registrations for change of residence to abroad.

**Mortality (rate of)**: ratio between the number of deaths in the year and the average amount of the resident population, multiplied by 1,000.

**Natural balance**: difference between the number of births and the number of deaths.

**Natural growth (rate)**: the difference between the birth rate and the death rate.

**Net migration with abroad (rate)**: the difference between the immigration rate from abroad and the emigration rate with abroad.

**Old age (index)**: ratio between the population aged 65 and over and the population aged 0-14, multiplied by 100.

**Predictive (or confidence) interval**: an interval associated with a random variable yet to be observed, with a specific probability that the random variable falls within it.

**Probabilistic demographic projection**: elaboration on the future development of a population, summarized in a set of values or in a probability distribution, in which the variables used are of a random nature that cannot be predicted with certainty and in which not all assumptions are equally probable.

**Probability of death**: the probability that an individual of precise age x will die before the birthday x + 1.

**Projection**: development expected in the future.

**Projection probability of death**: the probability that an individual of age x (in years completed on 1st January) will not survive within the year.

**Projection probability of interregional migration**: the probability that an individual of age x (in years completed on January 1st) moves residence between two regions before the end of the year.

**Range**: measure of the variability of a quantitative phenomenon defined by the difference between its maximum and the minimum value.

**Registration and de-registration for transfer of residence**: registration concerns people who have moved to a Municipality from other Municipalities or from abroad; the de-registration concerns people who have moved to another municipality or abroad.

**Resident population**: constituted in each Municipality (and similarly for other territorial divisions) of people with habitual residence in the Municipality itself. Persons temporarily residing in another Municipality or abroad, for the exercise of seasonal occupations or for reasons of limited duration, do not cease to belong to the resident population.

**Scenario approach**: the description of the context, even conceptual, in which the population is projected. In a deterministic approach it usually refers to the main or central assumption. In a stochastic it can refer to the assumption identified as mean or median.

**Simulation**: the quantitative implementation of a single set of demographic assumptions to be launched in the cohort-component model in order to obtain a single set of demographic projections.

**Total balance**: sum of the natural balance and the total migratory balance.

**Total growth (rate of)**: the sum of the total net migration rate and the natural growth rate.

**Total migratory balance**: the sum of the migration balance with abroad and the internal migration balance.

**Total net migration (rate)**: the sum of the net internal migration rate and the net migration rate with abroad.

### Population projection by sex, age and region

Full text and methodological note: Population and households projections