Teaching Tips: randomisation for trials

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  • Format Lessons
  • Language/s English
  • Target Audience Schools, Further education
  • EBM Stage 3 - Appraising evidence
  • Duration 5-15 mins
  • Difficulty Introductory

Key Concepts addressed


The educational solution
Students are handed an envelope as they enter the lecture theatre for a session introducing randomised controlled trials. They are asked not to open it until instructed.

The lecture proceeds. At the point when randomisation is discussed, the students are invited to supply some information about themselves: how many are female; live inter-state, have ever smoked etc. The data are written up on a white board in a Table.

Then I ask if anyone has already opened their envelope (almost invariably 1-2% have), and these data are also tabulated, also checking their state and past smoking status. I also ask if anyone has been able to work out what the envelopes contain: explaining that we put in two types of confectionery (popular brands of either a boiled, or minty, sweet). Some know, and I record this into the Table. And I ask how they were able to check (usually they have held the envelope to the light, or simply palpated its contents and guessed), recording this also. I ask them to check if they were right by fully opening their envelopes, recording how many guessed correctly (usually most). I invite everyone to open their envelope and consume their contents. Finally, I ask how many have swapped theirs with a neighbour because of preferences (usually surprisingly many).

The following discussion
After the commotion has settled down, I open a discussion, and ask the students to help me draw up a CONSORT statement of the outcomes of this RCT. The breaking of blinding is recorded, together with the attrition to the ‘other treatment’, and we use the previously collected data about the students to test if the randomisation was successful (the Baseline Table of so many reported RCTs).

Follow up
I test knowledge and understand by means of multiple choice questions in the end of year exams to check there is some persistent understanding. I also revisit the teaching session the following year when we start to critically appraise randomised controlled trials, pausing to talk about randomisation. This enables a spiral of learning re-enforcement.

Where the idea came from
Sandy Pirozzo was a lecturer in the Masters of Public Health program at the University of Queensland who was extremely original in her teaching ideas, and she devised these techniques.

Chris Del Mar cdelmar@bond.edu.au Oct 2017


Leave a Reply


Paul Glasziou 01:35am Sun 28 Oct 2018

Good short method to get folk to experience randomization. Can be slotted in a part of a lecture about trials or appraisal of studies, but remember to prepare the day before!

Bridget Abell 00:46am Mon 05 Nov 2018

I love this exercise! Still remember it from a CREBP workshop and actually used it last month in a tutorial for post-grad epi students. I had to make it up from memory but it seems I got most of it right. Went down really well.

Loai Albarqouni 05:14am Fri 28 Feb 2020

Great resources! We used a variation of it to teach randomisation and group allocation for a small number of a postgraduate subject in evidence-based practice. We used colourful beads and cards as demonstrated in this video https://www.youtube.com/watch?v=gqL6FX0pwDU. It went very well.

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