Year 9 Science · Unit 1 · Lesson 18
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Learning Goals
Compare two
Complete the table to compare the three main study designs used in epidemiology.
| Feature | RCT | Cohort study | Case-control study |
|---|---|---|---|
| Direction in time | |||
| Participants randomly assigned? | |||
| Good for rare diseases? | |||
| Main advantage | |||
| Main limitation |
Real-world context
In 1950, British epidemiologists Richard Doll and Austin Bradford Hill published a landmark case-control study examining smoking and lung cancer. They interviewed 709 lung cancer patients and 709 matched controls (hospital patients without lung cancer) about their smoking histories. The results showed that 647 of the 709 lung cancer patients were smokers, compared to only 622 of the 709 controls. Doll and Hill followed this with the British Doctors Cohort Study (1951–2001), which tracked over 34,000 doctors for 50 years and recorded who developed lung cancer and what they smoked.
(a) Identify the study design used in the 1950 Doll and Hill study and explain why this design was appropriate for investigating a rare disease like lung cancer at that time.
(b) Identify ONE potential confounding variable in the 1950 case-control study and explain how it could affect the results.
(c) Identify ONE ethical concern with the British Doctors Cohort Study and explain how researchers could address it while still obtaining valid data.
1. A news article claims "People who eat breakfast every day have lower rates of obesity." Explain whether this headline proves that eating breakfast prevents obesity. What study design would you need to establish causation?
2. In an RCT testing a new blood pressure drug, neither the patients nor the doctors administering the drug know who received the real drug and who received the placebo. What is this called, and why is it important?
Wrap Up
In one sentence, explain why correlation is not the same as causation in disease research.