Two groups receive different treatments in a medicine trial. Symptom severity is scored from 0 to 10, with higher scores indicating worse symptoms.
Table
| Treatment | Mean score before treatment | Mean score after treatment |
|---|---|---|
| Medicine | 8 | 4 |
| Placebo | 5 | 2 |
A student concludes that the medicine is more effective because its mean score decreased further.
Which statement best identifies a limitation of this conclusion?
Final severity differed, so the groups must have received identical active medicines.
Both groups improved, so the medicine must have had no biological effect.
Initial severity differed, so the groups may not provide a fair comparison.
Both groups improved, so the placebo must have contained the active medicine.
45 exam-style questions on Edexcel GCSE Biology 5.3 Immune system and medicines, covering 5.3.1 The specific immune system, 5.3.2 Response to immunisation, 5.3.3 Advantages and disadvantages of immunisation, 5.3.4 Antibiotics and bacterial infections, 5.3.5 Aseptic techniques in culturing, 5.3.6 Cross-sectional areas of cultures, 5.3.7 Stages of developing new medicines, and 5.3.8 Production of monoclonal antibodies. Each one has a worked solution and a mark scheme showing where the marks go.