## Zac Fact #16 (In The Land Of The Blind…)

I'm not a statistician by any means, but I will say an example from *High Yield Biostatistics* by Dr. Glaser really caught my attention. This stuff is pretty confusing, so I'm going to simplify his numbers a bit further.

There was a study called WOSCOPS that treated obese men with statins. WOSCOPS was a huge study, involving 6,000 men for 5 years. 3,000 of them were given the statin, and 3,000 were given placebo.

Over the course of the study, about **75** men in the placebo group died from heart attacks, while only **50** died in the statin group. We calculate the mortality rates for each group as 50/3000 = **1.6%**, and 75/3000 = **2.5%**.

Calculating the ** relative risk reduction** is easy:

**1 - (risk in the population of interest / risk in the population as a whole)**

1 - (1.6%/2.5%) =

**33%**

Therefore, the WOSCOPS study reported an incredible

*33% reduction in cardiovascular mortality from statins*. Amazing! Cardiologists everywhere rushed to put their patients on statins, right?

Not so fast.

The ** absolute risk reduction** is calculated by subtracting the 2 percentages. 2.5% - 1.6% =

**0.6%**. We then calculate the

**as**

*number needed to treat***1/ARR**. This comes out to

**166**... which means we would have to give 166 men statins for 5 years to prevent one of them dying from a heart attack. This reflects the fact that the heart attacks happened at a relatively low frequency in the study.

Multiply 166 people x $100 a month (the cost of the statin) x 60 months in the study... and you get roughly $1,000,000.

It costs **$1,000,000** to buy enough statins to save **one life** over a five year period. This is why healthcare costs so damn much.

AngelaJune 15th, 2007 - 07:40

Zac…I just want you to know that I read this post the night before my test, and I totally had a question about number needed to treat…which neither of our books went over! So, thanks!!

NellyJune 15th, 2007 - 11:22

Pretty good biostats analysis buddy!

NellyJune 18th, 2007 - 08:16

You typed the numbers into your calculator wrong. 2.5 – 1.6 = 0.9

NNT = ~ 111

P.S. Question: was there any decrease in morbitity noted in the study?