Statistical analysis Christian Gratzke LMU Munich Outline for 2017 - Cathy Hier Foto Ausgabe EU Focus Christian Gratzke LMU Munich Department of Urology London, March 2017

Urologists usually have a limited training in biostatistics Statistical Analysis Urologists usually have a limited training in biostatistics Statistics departments offer introductory courses to the world of biostatistics These courses are recommended before / when starting to conduct research

I usually do my statistics myself Statistical Analysis I usually do my statistics myself However, I always contact my biostatistician to double-check the results

Very complex statistical tests are seldom useful Statistical Analysis Very complex statistical tests are seldom useful Whenever used, they should be explained and referenced Fancy statistics are meaningless if not strictly related with the clinical problem What might be hard for an experienced reviewer will be impossible to understand for most of the readers

Statistical Analysis

Statistical Analysis

Slip Ups – and how to avoid them Dr. Andrew Vickers, Ph.D. Attending Research Methodologist MSKCC

Slip Up 1 It is not only about producing p values

Statistical Methods Inference Is something there? Hypothesis testing: p values Estimation How big is it? E.g. means, correlations, proportions, differences between groups

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

Inference State a null hypothesis

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

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

Slip Up 2 Don’t accept the null hypothesis In a court case: guilty or not guilty In a statistical test: reject or don’t reject

Slip up 3 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

Slip up 3 A result isn’t a conclusion

Slip up 4 Mean gestational time was 36.345 weeks in the experimental group compared to 36.229 weeks in controls (p=0.6945).

Slip up 4 Every number you write down means something

Slip up 5 Whereas 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.

Slip up 5 Multiple testing. Looked at 9 different biomarkers. 35% chance of at least one marker with p<0.05. A statistical association isn’t grounds for a change in practice.

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