Presentation on theme: "Reporting drugs and treatments Thomas Abraham. What we will learn today The difference between absolute and relative risk reduction A basic way to interpret."— Presentation transcript:
What we will learn today The difference between absolute and relative risk reduction A basic way to interpret P values and CI (confidence intervals) Number needed to treat (NNT) All of these are to help you evaluate and report on studies
Nov 1995, results of the trial of a drug announced 6,595 men in the west of Scotland with elevated cholesterol level 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
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
7.9% 5.5% Combined risk from heart attacks and death from heart disease
A 7.9% B 5.5% Control group Treatment group How do you measure the difference between these two groups? Risk from heart attack and death from heart disease
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 B Treatment 7.9% 5.5%
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
A Control 6.5% B Treatm ent 4.6% Non fatal Myocardial Infarction Absolute Risk= ? Relative risk= ?
What were the different outcomes the study measured? Which outcome was the treatment the most effective in?
P values and Confidence Intervals ( CI) P value or probability value= The probability that a result could have occurred by chance P <.05 means a less than 5 percent probability that this result could have occurred by chance P<.01 means a less than 1 percent probability that this could have occurred by chance P <.001 means ? (move decimal point two places to the right)
According to scientific convention, P<.05 is significant, and P<.01 is highly significant.
Rank the following P values in terms of significance A. P<.1 B. P<.001 C. P<.01 D. P<.4 E. P<.04 F. P<.5 G. P<.0001 H. P<.05
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.
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
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
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
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
From last week When evaluating research findings - Published or not published? - Quality of study: numbers of people or cases studied, methodology of study - Newsworthiness
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.
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
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
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)