Recap

Key points of the chapter:

• Data is a tool that helps us reach a sound conclusion about a problem.
• Primary data are based on first-hand information; secondary data are collected and processed by another agency.
• A survey can be done through personal interviews, mailed questionnaires or telephone interviews.
• A Census covers every individual or unit in the population, while a sample is a smaller group selected from the population to supply the needed information.
• In random sampling every individual has an equal chance of being selected; in non-random sampling the investigator's judgement or convenience decides.
• Sampling error is the difference between the sample estimate and the corresponding population parameter, and can be reduced by a larger sample. …