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Reporting drugs and treatments Thomas Abraham JMSC 6090

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What we will learn today How to evaluate and report on studies The difference between absolute and relative risk reduction Number needed to treat (NNT) A basic way to interpret P values and CI (confidence intervals)

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Nov 1995, results of a new drug trial 6,595 men in the west of Scotland with elevated cholesterol levels participated in trial that lasted 5 years One group (treatment group) was given a cholesterol lowering drug, pravastatin Another group (control group) was given a placebo

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The results were impressive For those who took the drug: 31 % reduction of risk from heart attacks 28 % reduction of risk of death from coronary heart disease 31 % reduction of risk from heart attack, or death from heart disease

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7.9% 5.5% Combined risk from heart attacks and death from heart disease

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A 7.9% B 5.5% Control groupTreatment group How do you measure the difference between these two groups? Risk from heart attack and death from heart disease

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Absolute and relative risk reduction Absolute risk reduction looks at the difference between the treatments: A-B =2.4% Relative risk reduction looks at how much better one treatment is than the other (A-B/ A) x 100=30.37% A Control group B Treatment Group 7.9% 5.5%

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Absolute and relative risk Absolute risk is your risk of getting a particular disease, or condition Relative risk measures how much your risk is reduced with the new treatment, or procedure, compared with the old. Relative risk figures tend to look dramatic

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Control: 1.7%; treatment 1.2% Absolute risk reduction= Relative risk reduction=

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A Control 6.5% B Treatm ent 4.6% Non fatal Myocardial Infarction Absolute Risk Reduction = ? Relative risk Reduction= ?

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What were the different outcomes the study measured? Which outcome was the treatment the most effective in?

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Number needed to Treat (NNT) The number of persons who needed to be treated with a drug, to prevent one person from getting the disease. Calculated as the inverse of the absolute risk reduction percentage

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Absolute Risk Reduction = A-B=.5%. 5% means out of 100 people,.5 death was prevented To prevent one death: 200 people need to be treated ( 100/ARR%) Time-5 years. Therefore 200 people over 5 years to prevent 1 case

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A Control 6.5% B Treatm ent 4.6% Non fatal Myocardial Infarction Absolute Risk Reduction = A-B= 2.9% Number needed to treat 100 people, 2.9 heart attacks prevented To prevent one heart attack= 100/ARR%= 100/2.9 Over 5 years

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Check list When you hear about a new drug or treatment, check both absolute and relative risk reduction figures. http://www.bbc.co.uk/news/health- 16961112 http://www.bbc.co.uk/news/health- 16961112 Ask ( or calculate) number needed to treat Ask about possible harms Ask about costs

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P values and Confidence Intervals ( CI) P value or probability value= “The probability of obtaining result at least as extreme if the null hypothesis was true” P <.05 means a less than 95 percent of the time you will get a similar result P<.01 means a less than 99% percent of the time you would get a similar result P values of.05 and less are acceptable

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According to scientific convention, P<.05 is significant, and P<.01 is highly significant.

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Confidence intervals (CI) The confidence level tells you the range within which a true value will lie. It is generally measured at the 95% level. For example, 31 ( 17-43) 95% CI would indicate that 95% probability that the real value is between 17 and 43.

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http://www.youtube.com/watch?v=lNFuEcy 5ekg&feature=related

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From last week When evaluating research findings - Published or not published? - Quality of study: numbers of people or cases studied, methodology of study - Newsworthiness

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Your course work Three news stories from journal articles Due Feb 28, March 28 and March 17(you can turn them in earlier if you wish) Length: 400-500 words Go to Eureka alert, as well as Jama and BMJ Links to press releases on our course website Find an article that you think might be newsworthy and interesting.

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Do some background research on the topic. Go to Pubmed for earlier studies Contact authors of paper, as well as people in Hong Kong who might have comments. Give yourself one week for each

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Contacting paper authors Why? Not to “get a quote” To help bring out the significance, or importance of study To help you understand things you do not understand Read the paper and do research before getting in touch, so you do not ask basic questions

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What I will look for Is the story newsworthy? Have you explained the research well? Have you looked at the costs and benefits (Look at the health news review website for an idea of what I will be looking for)

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Copyright © 2013, 2009, and 2007, Pearson Education, Inc. Chapter 10 Comparing Two Groups Section 10.1 Categorical Response: Comparing Two Proportions.

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