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[Instructor] Dear students.

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Today, we are going to go
over practice problem 13

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from Chapter 3.

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First, I will read the problem

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so we can understand what
information is given to us.

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Then, we will determine
how to answer the question.

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Problem 13 states a
randomized control trial

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was conducted to evaluate the
effect of hydroxychloroquine

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as a potential therapy

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to prevent COVID-19
infection following exposure.

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Exposed participants were randomized

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to receive hydroxychloroquine
or usual care

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and the primary outcome
was COVID-19 infection.

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The investigators also assessed

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the adverse event in each group

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and found that 56.1% of the patients

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in the hydroxychloroquine group

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experienced adverse events

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as compared to 5.9% in
the usual care group.

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So the problem is right now asking us

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to calculate the relative
risk of adverse event.

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To answer this question,

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first, we need to calculate
the relative risk,

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and for that, we have to use the formula.

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Again, relative risk is abbreviated as RR.

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Here,

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the numerator is PP exposed,

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and PP is our point prevalence,

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and the denominator is
point prevalence unexposed.

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So what is our exposure here?

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Our exposure is hydroxychloroquine.

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And PP, again, is our point prevalence.

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And our secondary outcome
here is the adverse event.

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So now as we try to calculate the RR,

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we have to insert the proper information

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that were provided to us.

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So the point prevalence
exposed will be 56.1%

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and the point prevalence
unexposed will be 5.9%.

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So the answer here will be 9.5,

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our c.

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Now, what does this mean?

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Anytime our relative risk
is different from one

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means that there is a
dissimilarity between the groups.

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So here, the group treated
with hydroxychloroquine

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is 9.5 times more likely

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to suffer from adverse events

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compared to the group
that received usual care.