1. Biostatistics Board Review Parul Chaudhri, DO Family Medicine Faculty Development Fellow, UPMC St Margaret March 5, 2016

2. Review key biostatistics concepts Understand 2 X 2 tables

3. Objectives By the end of this session, active participants will be able to: Identify key biostatistics concepts Break down the question into 2 X 2 tables Apply the key concepts to solve problems

4. It’s all about the 2X2 Association between Exposure and Outcome EXPOSURE DISEASE NO YES A/B = AD C/D BC A/ (A+B) C/ (C+D) RR= OR=

5. TEST DISEASE NO YES Sn TP (TP+ FN) TN (TN+ FP) Sp SpIN SnOUT

6. Which one of the following reflects the percentage of patients with a disease who have a positive test for the disease in question? 1.Likelihood ratio 2.Sensitivity 3.Specificity 4.Positive predictive value 5.Negative predictive value

7. In a study to evaluate a test as a screen for the presence of a disease, 235 of the 250 people with the disease had a positive test and 600 of the 680 people without the disease had a negative test. Based on this data, the specificity of the test for the disease is 1.235/250 = 94% 2.15/250 = 6% 3.600/680 = 88% 4.80/680 = 12% 5.15/80 = 19%

8. TEST DISEASE NO YES Sn Sp 600 (80+600) TP (TP+ FN)

9. PPV TEST DISEASE NO YES TP (TP+ FP) TN (TN+ FN) NPV Sn (1- Sp ) (1- Sn) Sp +LR = -LR =

10. A study finds that PPV of a new test for breast cancer is 75%, which means 1.If 100 patients with breast CA have the test, 75 (75%) will have a + result 2.If 100 patients without breast CA have the test, 75 (75%) will have a – test 3.75% of patients who test + actually have breast CA 4.75% of patients who test – don’t have breast CA

11. A home urine test is designed to detect a type of cancer. The gold standard for this cancer is a biopsy. The biopsy is more costly, invasive, and associated with lots of adverse side effects. To test the effectiveness of the home urine test, 104 people took the test and then agreed to a biopsy. When the study was concluded, 77 people tested negative and 27 tested positive on the urine test. Biopsies were positive in 18 individuals, 8 of whom tested negative on the urine test. What is the NPV of the home urine test, rounded to a whole number? 1.20% 2.37% 3.56% 4.80% 5.90%

12. TEST DISEASE NO YES NPV= 69/ 77= 89.6 %

13. A 69 year-old female with postmenopausal bleeding. You consider whether to do a vaginal US to assess the thickness of her endometrium. In evaluating the usefulness of this test to either support or exclude a diagnosis of endometrial cancer, which one of the following statistics is most useful? 1.Likelihood ratio 2.Number needed to treat 3.Prevalence 4.Incidence 5.Relative risk

14. Prevalence is the existence of a disease in the current population Incidence describes the occurrence of new cases of disease in a population over a defined time period Relative risk is the risk of an event in the experimental group versus the control group in a clinical trial The number needed to treat is useful for evaluating data regarding treatments, not diagnosis Other Terms

16. It’s all about the 2X2 Association between Exposure and Outcome TEST DISEASE NO YES Type I error Type II error Power= 1- Type II error

17. The results of a given study are reported as achieving significance at a p-value of <0.05 (the 5% level). True statements about this finding include which one of the following? 1.5% likelihood of the results having occurred by chance alone 2.If the study were replicated 100 times, 95 studies would repeat this finding and 5 would not 3.The confidence interval is 0%-10% 4.The null hypothesis has a 5% chance of being true 5.The β (type II) error is <5

18. A 95 % Confidence Interval Means 1.At least 95% of patients with a disease have a positive test for that disease 2.At least 95% of patients without a disease have a negative test for the disease 3.There is a 95% difference in risk between the treatment and control groups 4.It is 95% certain that the true value lies within the given range 5.At least 95% of the patients need to receive an intervention instead of the alternative in order for one additional patient to benefit

19. 95% confidence interval There is 95% certainty that the true value lies within the given interval range. P-value The probability of obtaining a result equal to or "more extreme" than what was actually observed, assuming that the null hypothesis is true OR Likelihood of achieving that result by chance alone

20. When a screening test identifies a cancer earlier, thereby increasing the time between diagnosis and death without prolonging life, this is called 1.Length-time bias 2.Lead-time bias 3.False-positive screening test 4.Increasing the positive predictive value of the screening test 5.Attributable risk

21. Bias Lead-time bias is when a screening test identifies a cancer earlier, thereby increasing the time between diagnosis and death without actually prolonging life. Length-time bias is when a screening test finds a disproportionate number of cases of slowly progressive disease and misses the aggressive cases, thereby leading to an overestimate of the effectiveness of the screening. Attributable risk is the amount of difference in risk for a disease that can be accounted for by a specific risk factor.

22. Results of a clinical study show a relative risk reduction (RRR) of 33% and an absolute risk reduction (ARR) of 20%. There are 1000 patients each in the treatment and control groups. To help determine the potential benefit of the treatment it is necessary to identify the number needed to treat (NNT). Which one of the following is the NNT for this clinical study? 1.3 2.5 3.13 4.130 5.The number cannot be determined from the information provided

23. Risk Reduction and Number Needed to Treat Number Needed to Treat (NNT): number of patients necessary to treat in order for one patient to benefit. Absolute Risk Reduction (ARR): Absolute adverse event rate for placebo minus the absolute adverse event rate for treated patients – Relative risk reduction (RRR): often quoted in the press or by those promoting a treatment, can be misleading to both the general public and to physicians. NNT= 1/ARR

24. Questions

25. References: Fletcher RW, Fletcher SW: Epidemiology: The Essentials, ed 4. Lippincott Williams & Wilkins, 2005 http://www.medpagetoday.com/lib/content/Medpa ge-Guide-to-Biostatistics.pdf http://www.medpagetoday.com/lib/content/Medpa ge-Guide-to-Biostatistics.pdf http://www.musc.edu/dc/icrebm/2x2table.html

26. Thank You Dr. Stephen Wilson UPMC St Margaret Faculty Development Fellows