316 A randomized cinical trial compared aspirin to placebo for the prevention of
ID: 3359826 • Letter: 3
Question
316 A randomized cinical trial compared aspirin to placebo for the prevention of heart attacks (Mls) and strokes Out of a total of 1,000 subjects on aspirin, there were 80 heart attacks and 65 strokes out of a total of 2,000 subjects on placebo, there were 240 heart attacks and 165 strokes Is there a significant benefit for aspirin therapy for heart attacks and strokes? What is the RR for aspirin use for each of these two outcomes? (Careful here, you are given the total number of subjects in each group and the number of complications)Explanation / Answer
as we are interested in reducing the heart attacks hecne this would be a directional test for proportions with the lesser sign
The R functions prop.test() can be used as follow:
prop.test(x, n, p = NULL, alternative = "two.sided",
correct = TRUE)
The R snippet is as
res <- prop.test(x = c(80, 240), n = c(1000, 2000),alternative ="less")
# Printing the results
res
The reuslts are
res
2-sample test for equality of proportions with continuity correction
data: c(80, 240) out of c(1000, 2000)
X-squared = 10.778, df = 1, p-value = 0.0005135 ## as the p value is less than 0.05 , hence we reject the null hypothesis in favor of alternate hypothesis to conclude that the aspirin has significantly reduced the heart attacks
alternative hypothesis: less
95 percent confidence interval:
-1.00000000 -0.02075728
sample estimates:
prop 1 prop 2
0.08 0.12
The risk ratio is
install.packages("fmsb")
library(fmsb)
riskratio(80, 240, 1000, 2000, conf.level=0.95)
Disease Nondisease Total
Exposed 80 920 1000
Nonexposed 240 1760 2000
Risk ratio estimate and its significance probability
data: 80 240 1000 2000
p-value = 0.0008223
95 percent confidence interval:
0.5236977 0.8486660
sample estimates:
[1] 0.6666667
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