sampling

• population

  the population is the group of people from whom the sample is drawn.
• opportunity sampling

  taking the sample from people who are available at the time the study is carried out and fit the criteria you are looking for.
• random sampling

  every member of the population has a chance of being chosen, selecting the number of participants you need in a way that everyone has an opportunity to be picked.
• self- selective sample


  participants becoming part off a study because they volunteer when asked or in response to an advert.
• stratified sampling

  classifying the population into samples then choosing a sample which consists of participants from each category in the same proportions as they are in the population.
• systematic sampling

  nth term, using a pre-determined system to select every nth participant.