IA Tips: How to explain your…SAMPLING TECHNIQUE

Travis DixonInternal Assessment (IB)

It's possible to get full marks in the IA, but you MUST pay attention to the little details.

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Explaining the sampling technique might just be the easiest part of the Exploration. Let’s look at how it can be done properly. The IB’s given some advice, too, but be careful – it’s not as straightforward as first appears.

The most common sampling technique is opportunity sampling (aka convenience sampling). Alternative choices include:

  • Random sampling
  • Volunteer sampling (aka self-selected sampling)
  • Purposive sampling*
  • Snowball sampling*

*These are not commonly used for experiments and should only be used under careful teacher supervision (I have had students in the past justify a use of a purposive sample).

Definitions of the above sampling methods are explained here.

More IA Exploration Tips. How to explain your:

3x Quick Tips

  1. Success in the IB IA is about careful planning and paying close attention to the details. What-How-Why is a great rule for the Exploration that makes this process easier.

    Is it a volunteer or opportunity sample? This can be difficult. If you’ve advertised your study and the people come to you, it’s a volunteer sample. If you’ve approached people at a particular time and place, it’s opportunity. The distinction can be made between who approaches whom. Sometimes there’s a fine line. Here are two common examples:

    1. Studying a whole class at one time because it’s available when you are (you approach them) = opportunity.
    2. Emailing a whole class and asking people to come to a particular location at a certain time if they want (they approach you) = volunteer.
  2. The main reason for a volunteer sample is having motivated participants. The main reason for an opportunity sample is convenience.
  3. Avoid random sampling. It’s time consuming, difficult to carry out effectively and is often misidentified as the sampling method. If you want to control for researcher bias, use random allocation to conditions.

How to “explain” the sampling technique?

If you’re using an opportunity sample, the IB has stated that you simply need to state that you used an opportunity sample and that the reason was because this was the most convenient choice.

The 22/22 exemplar on MyIB “explains” their sampling method in such an oversimplified fashion: “A sample of opportunity was used, guaranteeing that the sample was easily organized.”

Similarly, another exemplar on MyIB’s official site explained their sampling by saying “The method of sampling was opportunity as this was the most convenient method for achieving as much data required in the limited period.” The examiner for this one commented that “Sampling method stated and explained.” It seems this one-sentence “explanation” is sufficient. However, I still stick with my “What-How-Why” approach and you can keep reading to find out why.

Apparently this is sufficient for an explanation of a sampling method. With my own students in my own classes, however, I don’t accept this oversimplified explanation. Keep reading to see why.


I encourage my students to (a) state what method they used, (b) describe how they applied this method specifically and (c) give a reason why they did it. Here’s an example taken from my exemplar IA on media and body dissatisfaction to show the detail I expect (Note: this is an unethical IA that you can’t copy but it’s great for showing the steps):

Sampling Method: We gathered a self-selected sample by using our school’s intranet to advertise our study and ask for volunteers. Interested participants sent us an email and we followed-up with them with consent forms and to find a time to participate in the study. We used this method because we thought that measuring body satisfaction was a sensitive and personal topic, so we didn’t want people to feel any pressure to participate by asking them directly, so we let them self-select for participation.

Has the IB given bad advice?

Despite the IB’s assurance that a basic “explanation” of opportunity sampling is sufficient, I encourage my students to ignore this advice and stick to the What-How-Why approach. Here’s why.

  1. Without a description of how the method was applied, there’s no way for me to know that the sample was actually an opportunity sample and not something else.
  2. In their instructions on procedures, the IB states that it’s helpful to put procedures in the body of the report because they’ll be evaluated later. I don’t know why this same logic hasn’t been applied in this context – how can an explanation of a sample make sense if we don’t know how it was applied?
  3. It’s not clear if this limited explanation also applies to other sampling methods. Can a student say “We used a self-selected sample because we wanted motivated students?” I doubt this would be accepted by most examiners as sufficient. So why is one sampling method treated differently to another?
  4. This policy encourages all students to use an opportunity sample because it’s easier to apply and it’s easier to explain. This removes the careful thought that should go into all aspects of an experiment’s methodology.
  5. In another example on the MyIB’s website, the following explanation is given of a sample: “We used a sample of opportunity because it was available.” The examiner’s comments on this were “Sampling technique is identified and described in limited detail. There is no clear explanation of why this technique was chosen or how it was actually carried out” (emphasis added). Here we see at least this examiner is like me and is looking for the how. Who’s to say others aren’t the same when marking?

It’s another matter of personal preference – follow the IB’s advice on what is an explanation of an opportunity sample, or go a bit further and use the “What-How-Why” approach. I know which one I prefer.

What’s the bottom line? What-H0w-Why. You can’t go wrong.