A census is a statistical study in which all people in the group are surveyed.
The United States Census: Every ten years the United States undertakes the enormous task of counting the number of people in the country.
 
Questionnaires available online and door-to-door canvasing by employees of the Census Bureau are used to collect the data. The results of the census are used to determine the geographic distribution of the population in order to assign appropriate representation in the House of Representatives and funding for each region.
 
A sample is a statistical study in which only a portion of the group is surveyed.
Nielson ratings are the systems used to measure the sizes and types of audiences watching specific television programs in the United States. The preselected demographic viewers provide information about shows, networks, and viewing times.
Requirements for a sampling:Randomness - every element in the universal set or population has an equal chance of being selected.A sufficient quantity of elements in the population must be sampled.Reliability or fairness - determine the magnitude of the sampling error Data consists of related numerical information.
 
Data which is collected for the first time by an investigator is known as primary data and data which is collected from previous records or studies is called secondary data.
 
Ways of gathering data:
Interviews - one of the quickest ways to collect dataWritten surveys - can cover a wide area geographically(Mailed questionnaires receive the least amount of feedback.)Logs, charts and diaries