There are three conventional sources of obtaining population data namely census, sample survey and vital registration.
The most important source of population information (demographic data) that enables us to understand the population growth rate and its trends in a country is a census.
Its major characteristics include:
Universality: inclusion of all persons in a given area during the count,
Periodicity: census undertaking at regular time intervals with reference to a defined point of time usually 10 years and 5 years,
Simultaneity: undertaking census in a very limited time duration called the census day/night,
Government sponsorship being an expensive endeavor, and publication
This is a method in which a defined population/sample/ is selected with the view that the information acquired would represent the entire population.
This method is advantageous over census as costs can be greatly reduced, and it is simple to administer and taken much faster.
Sampling may also be used with censuses in order to obtain more detailed information to supplement census data.
However, sample surveys have inherent weaknesses related to sampling errors and inadequate coverage thereby demanding caution in their undertaking.
Data from most censuses and sample surveys include geographic location, age, sex, marital status, citizenship, and place of birth, relationship to the head of household, religion, educational characteristics, occupation, fertility, income, language, ethnic characteristics, disabilities and
Vital registration is a system of continuous, permanent, compulsory, and legal recording of the occurrence and the characteristics of vital events like births, deaths, marriages, divorces, and adoptions.
Vital registration data tend to be more precise than that of census/sample survey and the system provides time-series data.
Despite the enormous usefulness of population information, it could be noted that population data could suffer from inaccuracy resulting from: poor and inadequately financed methods of collection; poorly trained enumerator; suspicion and ignorance of censuses and false statements specially of age and income; constant changes in administrations; omission of
more inaccessible areas; as well as wide difference in connotation of terms like language, ethnicity, and occupation.
The errors are likely to be introduced at the stage of data collection, data processing, analyses and the writing up of the report. As such, the errors need to be detected and all the necessary adjustments made to enhance their usefulness.
According to the first-ever census return of 1984, the population of Ethiopia was 42.2 million. The estimated rate of growth of the population in 1984. The total population grew to 53.5 million in the second census held in 1994. The country’s population reached about 73.8 million in 2007.
The largest part of the population (80%) is rural based. Like many other developing countries,
Ethiopia has a youthful population where about 65 percent of the population is below 24 years of age.
The population is also unevenly distributed.