Lesson Idea: Sampling Methods – Practice for Paper 3

Travis DixonResearch Methodology, Revision and Exam Preparation

How do you get a group of people to participate in your study? Do you just go to where the people are (like a graduation) or do you let them come to you. Gathering a sample is a challenge researchers must address and while there are a range of options available, each one comes with their own strengths and limitations.

For IB Psychology Paper 3, students need to know the following five sampling methods:


Getting a sample can be trickier. Identifying which sampling method was used can be even trickier!

  • Opportunity/convenience
  • Random
  • Self-selected/volunteer
  • Snowball
  • Purposive

The stimulus material (summary of a study) that you are given in the exam may or may not state the sampling method used. Therefore, you need to be prepared to identify the method used based on the summary of how the participants were gathered. This activity is designed to get ready to be able to do this.

Your task is to read the following summaries of how researchers may gather participants and identify which sampling method has been used (This is similar to this activity based only on the first three of the above methods).

Note: Some of the following scenarios could be identified as two different methods – the key is you can justify your answer based on the definitions and characteristics of the method.

Which sampling method was used?

  • The Minnesota Center for twins has a web-page where if you’re a twin you can fill out your details if you want to be contacted about participating in their study.
  • A researcher studying the effects of alcohol visits an AA meeting and asks for participants.
  • On a college campus during registration (where all students have to attend and register for classes), a research assistant asks every 10th participant if they would like to participate in a study.
  • A college student doing her post-graduate work in dieting trends asks a group of friends from her gym to participate in her study. She then asks them to ask anyone they know who is dieting to contact her about being a participant so she can get a larger sample.
    woman girl fat fitness

    Be careful not to say that a study is a volunteer study because participants volunteered – nearly all participants volunteer for a study, regardless of the sampling method. (Photo by Public Domain Pictures on Pexels.com)

  • A Japanese researcher is interested in the attitudes of new fathers towards parenting so they visit a government run seminar for expecting parents (i.e. couples who are about to have their first baby). A team of research assistants with clipboards individually approach the father’s during breaks in the seminar to ask if they’d like to participate by filling out a short questionnaire.

Exam Tip: Read the stimulus material carefully, as there is a good chance the sample method that was used will be stated directly in the summary. If it is and you write about a different method, you will score 0 marks for Question 1b.


Opportunity/convenience: Gathering participants who happen to be available at the time of the study.

Random: A random sample is when every member of the target population has an equal chance of being asked to participate in the study.

Self-selected/volunteer: Participants are the ones that approach the researchers as volunteers to participate in the study, usually in response to some form of marketing or advertising from the researchers.

Snowball: A sample that gradually increases in size after a small number of seeds originally selected ask more people to participate. Purposive sampling may include an element of snowball sampling.

Purposive: A sample that has been gathered because they have a particular set of characteristics that make them suitable for study.

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