This chapter consists of statistical data on  population characteristics from the last national census of population and housing in 1375, a comparison between selected demographic items from previous censuses, and data on births, marriages and divorces.

  Following is a history of data production on population.

  During Qajar period, about 90 years ago, some discontinuous efforts were made for enumeration, which were often ad hoc and regional.

  In 1297 the Civil Registration Department was established to register the four vital events. Registration of data on births, deaths, marriages and divorces was a beginning for collection of  information on the country's population and an incentive to assign an organization to collect the related data.

  By the approval of a statute in 1303 , the responsibility of collection of required information was entrusted to the Ministry of the Interior. Undergoing several changes, the statute was legally approved by the former National Consultative Assembly and the Civil Registration Department was renamed "General Department of Statistics and Registration". The Department has continued its legal duties since 1349 under the revised title of "Civil Registration Organization".

  Approval of the first Census Act by the National Consultative Assembly in 1318 led to the implementation of the first population census in Tehran in the month of Esfand of the same year and in 33 more cities during the years 1319 and 1320. The project was delayed because of the 1320 political events. In Esfand 1331, the General Statistics Cooperation Organization was formed and in Farvardin 1332, the Census and Statistics Act was approved. In the same year, after detaching from the General Department of Statistics and Registration and joining to the General Statistics Cooperation   Organization,  the  Department   of  Census and Statistics undertook the responsibility of data collection exclusively. This Organization  was  transformed  into the General Department of Public Statistics affiliated to the Ministry of the Interior in 1334 and conducted the first national census of population and housing in1335.

   By the establishment of the General Department of Public Statistics and the implementation of the national census of population and housing in 1335, a new era began for the statistical activities, and subsequently different statistical surveys in various socio-economic areas were carried out every year. The increasing need of planning organizations for information and statistics as well as the need for a close cooperation between the main data producing organization and planning organizations led to the detachment of the General Department of Public Statistics from the Ministry of the Interior and its affiliation to the Plan Organization under the title of the Statistical Centre of Iran (SCI) in 1344.

   As its first major activity, the SCI conducted a  national census of population and housing in 1345.

   The establishment act of the SCI was revised in 1353 due to some considerations.

   After the approval of the new act and structural renewal of the Centre, it conducted the second national census of population and housing in 1355.

   The 1365 National Census of Population and Housing was the first under the Islamic Republic of Iran, the results of which provided required information for socio-economic development planning for the country.

   Unpredictable increase of population during the years 1355 to 1365 and extensive population movements due to the Iran-Iraq war (imposed war) exposed the statistical frames resulted from the 1365 National Census of Population and Housing to basic changes and this made the planners and accordingly the SCI find it essential to conduct a nationwide enumeration years before     the     next     decennial     census.   This

enumeration, accompanied with a sample survey for the first time in the country, was implemented in 1991 under the title of "1370 Multi-round Population Survey".The fourth national census of population and housing was carried out in 1375, the results of which are now the most proper means of socio-economic development planning.

   The statistics presented in this chapter consist of the 1375 National Census of Population and Housing results and a summary of previous censuses results including the 1370 Multi-round Population Survey. Moreover, statistics on the vital events of births, marriages and divorces have been extracted from registers prepared by the Civil Registration Organization.

   As for statistics presented, the following should be taken into consideration:

1. Unification of Ostans statistics is based on changes made in administrative divisions included in tables 2.8, 2.9, 2.17, using the detailed results of the 1375 Population and Housing Census.

2. Due to some problems preventing  production of reliable statistics on death, no related data is included.

 Definitions and concepts

 Population (under enumeration): members of all private settled and institutional households whose usual place of  residence is located in Iran at the time of enumeration, and members of      all private unsettled households. Foreign delegations, diplomatic corps and their families are excluded. However, Iranian delegations and members  of  Iranian  diplomatic corps and  their

families at Iranian embassies in foreign countries are included in the population under enumeration.

 Household: persons living together in one residence, sharing their living expenses and eating together  constitute a household. A person living alone also forms a household.

 Private household: households falling under above definition, which comprise the greatest part of the country's  population.

Private settled household: a household living in a permanent residence at the time of the enumeration.

Private unsettled household: a household not living in a permanent residence at the time of the enumeration.This group of households includes three types:

1. households either moving from one  area to another   or   living   under   tents  outside  cities  and villages at the time of the census enumeration;

 2. households that do not live in a permanent place and change their living places continually, such as gipsies;

 3. households that do not live in a specific place and usually pass the night at parks, in ruined places, under bridges, etc.

 Institutional household: persons who share a common objective or characteristic such as military service,  education, mental disorders, etc., living together in an institution such as barracks, student dormitories, asylums, etc.

Age: number of completed years since the date of birth.

 City (urban area): every district with a municipality. In censuses before 1365, all Shahrestan  centres (irrespective of their population size)  and  places  with a population of 5000 persons and more were considered as city.

 Village (rural area): one or more contiguous places and lands (agricultural or  non-agricultural) located outside city borders and having independent registered or conventional boundaries. Any village inhabited by one or more households at the  time of  enumeration is considered as an "inhabited village", otherwise, it is considered as an "uninhabited village".

 Head of household: the person in the household who is acknowledged the head by other household members. If the household members are not able to nominate the head of household, the oldest member of the household is considered as the household head. In one-member households, the only member is considered the head.

Next of kin: spouse, child, father, mother,    brother and sister of the head of the household. Migrants: members of private settled and institutional households who have changed their place of residence  during the years 1365 to 1375. However, those members of household who have been away from their place of residence because of education or occupation in another country, or captivity and missing in action during the last ten years preceding the enumeration, but have joined their households by the time of the census, are not regarded as migrants.

 Mean age: average age of the population.

 Median age: the age which divides the population into two equal groups in number