1. What are the Chances Dr? Nick Pendleton

2. Can I have a Prostate Check? ?

4. Prevalence vs Incidence Prevalence: How much of a disease or condition there is in a population at a given point in time. Eg 181,463 men were alive with prostate cancer on 31 st December 2006 in UK Incidence: the rate of occurence of new cases of a disease or condition in a time period 2008 new cases of prostate cancer = 37,051 = rate of 97.9 per 100,000 population/year

5. The Digital Rectal Exam How good a test is it at determining whether a man has prostate cancer or not? If it was normal would that be reassuring?

6. How good a test is DRE? Meta-analysis 1999, Hoogendam et al. 14 studies, compared and pooled results Answer: High specificity and negative predictive value, low sensitivity and positive predictive value Neither a positive or negative test is enough to enable conclusions with out further confirmation

7. Specificity Sensitivity Positive predictive value (PPV) Negative predictive value (NPV)

8. Terrorists on a Plane http://understandinguncertainty.org/dishonesty

9. The Scanner The government have developed a scanner that can identify terrorists with 95% accuracy An informant says that 1 person on the plane is a terrorist out of the 100 passengers aboard

10. The man sat next to you tests positive! What are the chances that you really were sat next to a terrorist?

11. How sure are you? The scanner is 95% accurate and very sensitive So when the terrorist is scanned he will probably test +ve Of the 99 people who are not terrorists 5% (approx 5 people) will also incorrectly test +ve 6 people have tested +ve Therefore there is only a 1 in 6 chance that the man sat next to you is actually a terrorist!

12. The scanner was very sensitive but not very specific The proportion of positive tests that were accurate was low (low PPV) But the proportion of negative tests that were accurate was high (high NPV)

13. Meta-analysis What is it? What are the advantages? What are the challenges for those undertaking Meta-analysis?

14. A Forest Plot of Meta-analysis Results Keech et al. Results from the LIPID trial. 2003. Diabetes Care

15. RISK RATIO A measure of a certain event happening in one group compared to another group Eg coronary events in statin group vs placebo group = 1 there is no difference between statin & placebo >1 exposure to statin increases risk <1 the statin decreased the risk

16. A Forest Plot of Meta-analysis Results Keech et al. Results from the LIPID trial. 2003. Diabetes Care

17. 95% confidence interval How accurate is the result? P value: whats the chance the results occurred by chance?

18. A Forest Plot of Meta-analysis Results Keech et al. Results from the LIPID trial. 2003. Diabetes Care

19. PSA Counselling What are the risks? How sensitive is the test? How specific is it? Why do we not screen every man?

20. Conditions which may have elevated PSA Causes include: Acute urinary retention Benign prostatic hyperplasia Old age Prostatitis Prostate carcinoma Transurethral resection of the prostate Urinary catheterisation

21. Wilson-Jungner Screening Criteria The condition being screened for should be an important health problem The natural history of the condition should be well understood There should be a detectable early stage Treatment at an early stage should be of more benefit than at a later stage A suitable test should be devised for the early stage The test should be acceptable to patients

22. Wilson-Jungner Screening Criteria Intervals for repeating the test should be determined Adequate health service provision should be made for the extra clinical workload resulting from screening The risks, both physical and psychological, should be less than the benefits The costs should be balanced against the benefits

24. The PSA Test Prostate cancer is but one of several causes of a raised PSA test Because the test is non-specific, all patients with a significantly raised PSA should have a prostate biopsy One in five men with a normal PSA will have prostate cancer Two out of three men with a raised PSA will not have cancer cells in their biopsy

25. The PSA Test There is no conclusive evidence that detection of early prostate cancer leads to longer survival The test cannot distinguish between aggressive and slow-growing cancers and may detect tumours that would not otherwise become evident in the patient's lifetime The test is of most value in patients who are 'high- risk' - i.e: – Aged above 70 years – Afro-Caribbeans – Patients with a positive family history

26. The PSA result comes back PSA Cut-off Values Age (years)PSA Cut-off (ng/mL) 50-59≥3.0 60-69≥4.0 70 and over>5.0

27. What are the next steps? What do you say to him? What are the risks?

28. Ulrtasound-Guided Needle Biopsy

29. What is the chance of having an MI? We can work out the absolute risk using risk calculators. Framingham, Edinburgh, JBS2, Q risk Relative risk compares the effects of exposure to a risk factor eg. MI risk in smokers vs non-smokers

30. Relative risk reduction What is the reduction in risk of MI experienced by stopping smoking compared to someone who continues to smoke? Consider the reduction in risk of MI in treating an at risk patient with a statin versus someone of the same risk who does not receive a statin

32. Treatment vs Harm Numbers needed to Treat (NNT) How many people do we need to treat to prevent 1 MI Numbers needed to Harm (NNH): How many people do we need to treat to see a harmful side effect?

33. Explaining risk to Patients Is easier if you understand the risks Keep it simple Appropriate language for the patient Give examples Give meaningful comparisons Draw or show graphs or illustrations Use other resources Document explanation of risk

35. Small numbers 0.8% risk this means the risk is less than 1 in 100 0.008% risk is 8 in 100,000 0.0008 % risk is 8 in 1 million

36. ‘What difference does it make?’ Risk of MI 2% over 5 years 1% over 5 years with Aspirin

37. Resources 2 different but complementary statistics handouts will be uploaded to Bolton Medical Learning Zone – Read them! Next session: Malcolm Brown & Chris Lobo 28 th Feb