Reporting drugs and treatments

Thomas Abraham

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

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 B

Treatment7.9%

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

0.1

0.3

0.5

0.7

0.9

1.1

1.3

1.5

1.7

Death from coronary heart disease

Series1

AControl1.7 %

BTreatment1.2%

Absolute risk reduction= Relative risk reduction=

AControl6.5% B

Treatment 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<.1B. P<.001C. P<.01D. P<.4E. P<.04F. P<.5G. P<.0001H. 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

0.1

0.3

0.5

0.7

0.9

1.1

1.3

1.5

1.7

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

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)