Data collection

• What is a population?

  A population is the whole set of items that are of interest.
• What is a census?

  A census observes or measures every member of the population.
• What is a sample?

  A selection of observations taken from a subset of the population which is used to find out information about the population as a whole.
• Random sampling - Each item in the population has an equal chance of being chosen
• Stratified random sampling - The population is divided into groups (strata) based on some characteristic, then samples are selected randomly within each stratum.
• Systematic sampling - Every nth item is selected at regular intervals.
• Quota sampling - Members of the population are grouped according to certain characteristics, then a quota of people with these characteristics are interviewed.
• Convenience sampling - Samples are collected using whatever method is easiest and most convenient.
• Convenience sampling - Items are selected because they are easy to access or convenient to measure.
• Systematic sampling - Every nth item is selected at regular intervals throughout the population.
• Convenience sampling - People who happen to be available are asked to participate in the survey.
• Opportunity sampling - Those available when the researcher arrives are included in the sample.