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We asked members of the PHARMA-MKTING online discussion forum to solve the following clinical trial “brain teaser”: Sometimes, not all the critical data from a trial are available and you need to do some math to calculate risk. Here’s an example:
• There were 2,643 people in a study comparing naproxen to Celebrex. 702 took naproxen, 1057
• There were a total of 70 cardiovascular events among all the study participants. • The proportion of people having an event was 50% higher in the naproxen group compared to
• There was no increased risk for people taking Celebrex compared to placebo. You can assume that
the Celebrex risk was the same as the placebo risk.
Using the above information, please answer the following questions.
1. Calculate the likely magnitude of the naproxen risk, i.e., what percent of people taking naproxen
experienced a cardiovascular event compared to people taking placebo?
A: Naproxen % Risk of CV event? B. Placebo % Risk of CV event?
2. What would these numbers be if no (0) people taking Celebrex in this trial experienced a
A: Naproxen % Risk of CV event? B. Placebo % Risk of CV event?
See the table below, which shows responses (each row represents the answers from a single respondent). Only 1 respondent got it right. See the next page for the math and correct answers.
Q1A Q1B Q2A Q2B
0.0% 0.0% 0.0% 0.0% 0.3% 0.1% 0.3% 0.1% 1.7% 1.1% 6.5% 2.1% 2.0% 2.0% 2.0% 2.0% 3.0% 2.0% 5.0% 3.5% 3.7% 2.4% 3.7% 4.1% 3.7% 2.5% 5.0% 3.3% 3.9% 2.6% 5.4% 3.6% 4.4% 2.2% 5.7% 2.8% 4.9% 2.5% 0.0% 0.0% 5.0% 2.0% 5.0% 2.0% 5.0% 1.6% 0.0% 0.0% 5.0% 3.0% 4.0% 2.0%
20.0% 10.0% 42.0% 28.0% 50.0% 0.0% 50.0% 0.0%
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The chart on the right—taken from the INPUT 1: There were a total of 2,463 people in the study. naproxen celebrex
for calculating the number of people experiencing a CV event in each arm of the
study: Let X=number of people taking naproxen,
INPUT 2: There were a total of 70 events in the 3 groups.
in naproxen group
in placebo group
in celebrex group
26 (X) people taking naproxen experienced a
CV event; this represents 3.7% of the 704 people in the study taking naproxen. This is the correct answer for Q1A.
INPUT 3:The proportion of people having an “event” was 50% higher in the naproxen group
Y, which is the number of people taking placebo
who experienced a CV event, is also 26. Since
there were 1057 people in this group, the
naproxen
percent experiencing a CV event is 26/1057 =
2.5%. This is the correct answer to Q1B.
Note that 3.7% is 50% greater than 2.5%, which
satisfies one of the initial conditions. Many respondents obviously did not check their math by confirming that their results satisfied this
INPUT 4: There was no increased risk for people taking celecoxib compared to placebo.
For Q2, we assume no people taking Celebrex
experienced a CV event. Therefore, Z=0 and
celebrex
X+Y=70. X still equals 0.996Y to satisfy the 50%
condition, which still applies. Therefore,
substituting 0.996Y for X in the X+Y=70 equation gives us 1.996Y=70 and
Y=70/1.996=35, which represents 5.0% of the people taking naproxen (35/704). Rounding off, X also equals 35, which represents 3.3% of the people taking placebo.
CALCULATION: Substituting into original equation and solving for Y
The correct answers, therefore, are as follows:
Q1A: 3.7% Q1B: 2.5% Q2A: 5.0% Q2B: 3.3%
We round the values as follows: X = 26 Y = 26 Z = 18

Om artikelförfattaren Artikelförfattaren Christer Svensson är utbildad civilingenjör i kemiteknik från Chalmers Tekniska Högskola i Göteborg. Han har också arbetat och undervisat på samma ställe. Han har varit verksam inom batteribranschen i nästan 30 år och har haft ansvar för olika uppgifter inom produktion och utveckling av batterier. Detta gäller bland annat batterier

The pharmacological treatment of epilepsy in adults Lancet Neurol 2011; 10: 446–56 Treatment decisions in epilepsy need to be individualised on the basis of careful analysis of the risk-beneﬁ t ratio of Clinical Pharmacology Unit, each available option. Key decision steps include the time at which antiepileptic drug treatment should be started, Department of Internal