Sampling techniques

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Opportunity Sample

Sample of participants produced by selecting people there at the time.


  • Quicker and easier than other methods as the participants are already available.


  • Non-representative as the kinds of people available are likely to be limited, and therefore similar, making the sample biased.
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Random Sample

Participants selected using a random-number technique. Either through drawn from a hat or using random number generator.


  • Should be representative as all types of people in the population are equally likely to be chosen.


  • Difficult as everyone in the population must be equally likely to be chosen but this is hard to achieve e.g. through ack of information or access, and even then the sample may be biased e.g. if only girls happen to be selected.
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Self-selcting (volunteer) sample

Participants are selected by asking for volunteers, for example, placing an advertisement on college noticeboard. Can access a variety of particiapants if advertisement is in the newspaper, making the sample more representative.


  • Relatively easy because the participants come to you and are committed e.g. likely to turn up or repeat testing.


  • Non-representative as the kinds of people who respond to requests are likely to be similar e.g. better educated or have free time
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Snowball sample

Relies in referrals from initial participants to generate additional participants.


  • The chain referral process allows the researcher to reach populations that are difficult to sample when using other sampling methods.
  • The process is cheap, simple and cost-efficient.
  • This sampling technique needs little planning and a smaller workforce compared with other sampling techniques.
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