Teaching Research Methods - Sampling techniques

Sampling Sweets!

Relevant for GCSE and A-Level

When I started teaching, I always thought sampling techniques would be one of the easier parts of Research Methods to teach. Yet students really seem to struggle with them, especially stratified sampling. I've found that they find it really difficult to imagine how you can create a sample that proportionally represents the target population (and what 'proportionally represents' means!). They also struggle with a true definition of 'random' sampling rather than their definitions of random from everyday life. So to help with this, I use a practical strategy that they love - sweet sampling!

A few things to note before we get into the strategy:

1. This is a GCSE lesson for the new Edexcel GCSE (teaching from September 2017) Specification so systematic sampling is not included (I'll go through how I do it for A-Level though).
2. My school uses a bronze, silver, gold medal system for differentiation. This can be used to give students choice (so they can complete either the bronze, silver or gold task) or they can work their way up the medals to earn gold and go from the 'easiest' task to the most 'difficult.' We then use challenge tasks to really extend the thinking of the top end.
3. On the GCSE specification, sampling techniques are called sampling methods.
4. This activity works best with Smarties, especially the mini-ones, but will work with any pack of sweets where there are multiple colours and a fairly large amount of sweets in a pack. We tend to buy multi-packs of mini-smarties. Otherwise, you have to create a sample smaller than 20 which doesn't work so well for stratified sampling.
5. I'm pretty sure I read about this activity somewhere and I modified it to suit my purposes so I can't take full credit.

Step 1 - guess the technique

In pairs, students match the name of the method/technique to its picture. Using the pictures, they then try to guess how the researchers would select their participants.

This then leads to whole class feedback and a quick definition of each method/technique.




Step 2 - stratified sweet sampling

In pairs/small groups (depending on class sizes and numbers of sweets), students are given a pack of sweets, a pen and a piece of A4 plain paper (you'll see why later on).

As students find stratified sampling particularly difficult, I guide them through this one. They are given the following instructions:

1st step: count the number of sweets you have in total.
2nd step: count the number of each colour.
3rd step: you want to study 20 sweets, but you want to study them in proportion. How could you work this out?

The challenge task here is about selecting the individual sweets. Say they've calculated that they need three orange sweets. How do they decide which orange sweets should be in their sample? This then gets them to think about how it should be determined randomly and how they could do this (e.g. number the sweets and pick numbers out of a hat).

We then go through how they would have to divide the number of the colour by the number in total, and then times the answer by 20, and students create their stratified sample. Students then take a photo of their sample to refer to later, or they note down the number of each coloured sweet in their sample for the same reason.

Step 3 - sampling sweets

In their groups, students then do the task on the slide opposite, taking a photo/noting the number of different coloured sweets in each sample. Encourage the students to be creative and use the paper and pen where necessary. Using the same packet of sweets, they select a sample of 20 participant sweets using random sampling (they can use the paper to make a container and pick out 20 randomly or use the paper to number the sweets and pick numbers out of a hat), opportunity sampling (choose the 20 closest to them on the table) and volunteer sampling (they can use the pen to draw arms for the sweets and have 20 raise their hands to volunteer). If you want to add systematic for A-Level, they can they put the sweets into an order (e.g. alphabetical by colour) and pick out every nth sweet to participate until they have 20. I did the bronze, silver, gold by how easy it is to think of how to create the sample in this context, rather than the difficulty of the concept generally. The challenge task (where the pictures come in) also gives them a good introduction to the strengths and weaknesses of the different sampling methods/techniques.

This activity really helps them when it comes to identifying sampling techniques/methods, describing how they work and explaining the strengths and weaknesses of them. Give it a go and let me know how it works out.