A coach has 24 athletes try a new training regimen and compares their times to last year's times for the same athletes. Times improve, and he concludes the regimen works.
The most serious flaw is
- A
Times should be measured more often
- B
The sample size is too small
- C
Random sampling was not used
- Dcheck_circle
No control group; improvement may be due to natural development or other factors
Explanation
Without a control group, we cannot rule out alternative explanations (maturation, weather, motivation, etc.) for the observed improvement.