1. Common Statistical Errors (and how to avoid them)

2. Conflict of Interest Disclosure
I have no potential conflict of interest to report

3. A quick tour of common statistical errors
Advice to help your submission pass statistical review

4. Pop quiz: p values

5. Can you spot the error?

6. Bill Gates walks into a room…

9. Error 1
DATA
STATISTICIAN
P VALUES

10. Consultation Collaboration Partnership
Biostatisticians
Consultation
The statistician works on a single paper or protocol as a once-off
Collaboration
The statistician works with you on all of your projects over many years
Partnership
The statistician is a key part of the research team and develops scientific ideas

11. Statisticians can also help with…
Thinking through the scientific question Experimental design Data collection Data quality assurance

12. Inference: is something there?

13. Estimation: How big is it?
Mean
Median
Proportion

15. 10% reduction in breast cancer incidence P=0.07
Trial Results
10% reduction in breast cancer incidence P=0.07

16. Messi beats me 5 – 1 P = 0.08 by binomial test
Error 2
Messi beats me 5 – 1 P = 0.08 by binomial test

17. I could play for Barcelona!
Error 2
I could play for Barcelona!

18. State a null hypothesis
Inference 101
State a null hypothesis

19. State a null hypothesis Get your data, calculate p value
Inference 101
State a null hypothesis Get your data, calculate p value

20. Inference 101
State a null hypothesis Get your data, calculate p value If p<5%, reject null hypothesis If p ≥5%, don’t reject null hypothesis

21. Inference 101
Don’t accept the null hypothesis In a court case: guilty or not guilty In a statistical test: reject or don’t reject

22. Barcelona still hasn’t called.
Error 2
Barcelona still hasn’t called.

23. Which is bigger?

24. Error 3
“At randomization, there was a statistically significant difference in age between the drug and placebo group (p=0.04).” “Erectile function decreased in older men during the two-year follow-up period (p<0.0001).”

25. Don’t run a statistical test if you already know the answer
Error 3
Don’t run a statistical test if you already know the answer

26. Error 4
Erk3, ECAD, P21, P53, Cadherin, il 6, il12 and Jak had no association with outcome (p>0.2 for all), Ki67 was a predictor of recurrence (p=0.03). We recommend that Ki67 be measured to determined eligibility for adjuvant chemotherapy.

27. Looked at 9 different biomarkers.
Error 4
Multiple testing:
Looked at 9 different biomarkers.
35% chance of at least one marker with p<0.05.
1 significant p-value is not grounds to change practice.

28. Error 4
Every single p value tests a hypothesis Think carefully about every scientific question you want to ask

29. Error 5
RESULTS: Compared with a BMI of 18.5 to 21.9 kg/m2 at age 18 years, the hazard ratio for premature death was 2.79 (CI, 2.04 to 3.81) for a BMI of 30 kg/m2 or greater. CONCLUSION: Moderately higher adiposity at age 18 years is associated with increased premature death in younger and middle-aged U.S. women

30. A RESULT IS NOT A CONCLUSION!
Error 5
A RESULT IS NOT A CONCLUSION!

31. Biostatistics
Biology
Math

32. Error 5
OLD CONCLUSION: Moderately higher adiposity at age 18 years is associated with increased premature death in younger and middle-aged U.S. women NEW CONCLUSION:

33. Error 5
OLD CONCLUSION: Moderately higher adiposity at age 18 years is associated with increased premature death in younger and middle-aged U.S. women NEW CONCLUSION: Public health interventions should relay the risks of premature death among overweight women to encourage teen girls to avoid obesity.

34. Error 6
Mean gestational time was weeks in the experimental group compared to weeks in controls (p=0.6945).

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45. Simple Statistical Errors
Melissa Assel Research Biostatistician Memorial Sloan Kettering Cancer Center