Reporting drugs and treatments

Reporting drugs and treatments

Thomas AbrahamJMSC 6090

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)

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

The results were impressiveFor 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

A7.9%

B5.5%

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%

AControl group

BTreatment

Group

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

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

Death from coronary heart disease

Series1

AControl1.7 %

BTreatment1.2%

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

AControl6.5% B

Treatment 4.6%

Non fatal Myocardial Infarction

Absolute Risk Reduction = ? Relative risk Reduction= ?

What were the different outcomes the study measured?

Which outcome was the treatment the most effective in?

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

00.20.40.60.8

11.21.41.61.8

Death from coronary heart disease

Control1.7 %

BTreatment1.2%

A

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

AControl6.5% B

Treatment 4.6%

Non fatal Myocardial Infarction

Absolute Risk Reduction = A-B= 2.9%Number needed to treat 100 people, 2.9 heart attacks preventedTo prevent one heart attack= 100/ARR%= 100/2.9Over 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

Ask ( or calculate) number needed to treat

Ask about possible harms Ask about costs

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

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

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.

http://www.youtube.com/watch?v=lNFuEcy5ekg&feature=related

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)