Experimental Design Statistics Example 3
Follow the full solution, then compare it with the other examples linked below.
Example 3
mediumA doctor tests a new headache medicine. She gives the medicine to patients who ask for it and compares their recovery to patients who didn't ask. Identify at least two problems with this experimental design.
Solution
- 1 Step 1: No random assignment — patients self-selected into groups. Those who asked for medicine may have had worse headaches (or be more proactive about health), introducing selection bias.
- 2 Step 2: No placebo control — the improvement could be due to the placebo effect (patients feel better because they believe they received treatment, not because the medicine works).
Answer
Problems: (1) no random assignment — self-selection creates biased groups, (2) no placebo control — any improvement could be the placebo effect rather than the medicine's actual effectiveness.
Medical experiments require random assignment and placebo controls to establish that the treatment truly works. Self-selection introduces confounding variables, and the placebo effect can produce real improvements even from inactive treatments.
About Experimental Design
Experimental design is the careful planning of experiments to establish cause-and-effect relationships by controlling variables, using comparison groups, and randomly assigning subjects to treatment and control conditions to isolate the effect of interest.
Learn more about Experimental Design →More Experimental Design Examples
Example 1 easy
A farmer wants to test whether a new fertiliser improves crop yield. She applies the new fertiliser
Example 2 mediumDescribe the key components of a well-designed experiment to test whether a new study method improve
Example 4 hardDesign a double-blind experiment to test whether caffeine improves reaction time. Specify: (a) how p