Constructing your comparison group.

Random allocation is the most robust way to establish a comparison group, but it is not always practical to run a trial in this way. For example, if you want to evaluate the impact of a new sanctions and rewards system, it would not be possible (or ethical) to give only half the school access to rewards for good behaviour or effort. In this case, a matched comparison group is more suitable.

There are three broad categories for establishing a comparison group:

  1. Random allocation
  2. Matching
  3. Simple comparison

Random allocation

Random allocation involves one 'population' of pupils being allocated randomly into an intervention group, where they will receive something new (such as a new style of teaching, or a specific intervention to improve numeracy skills for example), and a control group, where they will continue receiving their education as usual. The population may a specific group of pupils (e.g. Pupil Premium), a year group, or a subject group. The most important thing to remember with random allocation is that once pupils have been assigned to a group they cannot change. If you have pupils change groups this will alter the randomness of the random allocation and it will no longer be a valid randomised controlled trial. Randomising pupils is a relatively straight forward process involving three steps. Click here for a step by step guide or watch a short guide here:

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Your comparison

For an interactive guide to choosing the design of your comparison group, start the Decision Tree in the righthand box

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