Sampling

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  • Sampling
    • Random Sampling
      • Definition-Every person in the target population has an equal chance of being selected
        • How to obtain: random techniques e.g lottery method
          • Strengths: Potentially unbiased as all members have an equal chance of selection
            • Limitations: does not guarantee the sample will be representative of the whole population, can be difficult to get a list of the whole population and contact those selected
    • Opportunity Sampling
      • Definition: the researcher picks anyone who is available to take part
        • How to obtain:approach anyone who is most convenient or most available e.g people walking by you in the street.
          • Strengths: easy, saves time and money. Limitations: biased as sample drawn from a small part of the population, ethical issues, students may feel obligated to take part
    • Volunteer Sampling
      • Definition: participants self select i.e they put themselves forward for inclusion
      • How to obtain: advertise for volunteers e.g in a newspaper, notice board etc
        • Strengths: gives access to a variety of participants, sample less biased, more representative. Limitations: volunteer bias-pps are usually more motivated than randomly selected pps, only literate people may respond.
    • Systematic Sampling
      • Definition: A sample is obtained by using every nth person where n is any number
        • How to obtain: use a predetermined system e,g select every 6th, 14th, 20th person from a phonebook
          • Strengths: unbiased because pps are selected using an objective system. Limitations: not truly unbiased unless you select a number using a method and start with this method and start with this person and then select every nth person.
    • Stratified Sampling
      • Definitions: subgroups(or strata) within a population are identified(e.g boys and girls, or age groups: 10-12 years, 13-15 etc. Participants are obtained from each of the strata in proportion to their occurence in the population, Selection from the strata is done using a random technique.

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