Section 1: Biases -- Lead Time Bias -- Length Time Bias -- Immortal Time Bias -- Selection bias -- Ascertainment bias -- Publication bias -- Berkson's Bias -- Section 2 Time effects -- Hawthorne Effect -- Will Rogers Phenomenon -- Section 3 Confounding -- Confounding by Severity -- Simpson's paradox -- Section 4 Misuse of tests -- Multiple comparisons -- Validation -- Proportional hazard violation.-Changing endpoints -- Section 5 Power -- Underpowering -- Overpowering -- Conclusion.