A clinical trial is conducted to compare ans experimental medication to placebo
ID: 2960219 • Letter: A
Question
A clinical trial is conducted to compare ans experimental medication to placebo to reduce the symptoms of asthma. Two hundred participants are enrolled in the study and randomized to receive either the experimental medication or placebo. The primary outcome is a self-reported reduction of symptoms. Among 100 participants who received the experimental medication, 38 reported a reduction of symptoms as compared to 21 participants of 100 assigned to the placebo.a. Generate a 95% CI for the difference in proportions of participants reporting a reduction of symptoms between the experimental and placebo groups.
b.Estimate the RR for reduction in symptoms between groups.
c. Estimate the OR for reduction in symptoms between groups.
d. Generate a 95% CI for the RR.
CI is Confidence Interval
OR is Odds ratio
RR is relative risk
Explanation / Answer
Percentage of people who reported a reduction of symptoms after receiving the experimental medication = 38% = 0.38
Percentage of people who reported a reduction of symptoms assigned to the placebo = 21% = 0.21
Difference in proportions of participants reporting a reduction of symptoms between the experimental and placebo group = 0.38 - 0.21 = 0.17
? = sqrt[ P * ( 1 - P ) / n ]
n = 100
P = 0.17
Thus, ? = 0.037
z = (p - P) / ?
At 95% confidence , Z =+1.96 and -1.96
+1.96 = (p - 0.17)/0.037
p = 0.243
-1.96 = (p - 0.17)/0.037
p = 0.096
Thus the 95% confidence interval is 0.096 < 0.17 < 0.243
b)The relative risk is the ratio of the proportions of cases having a positive outcome in two groups
RR = 0.38/0.21 = 1.809
c) Odds Ratio = (0.38/(1-0.38) / (0.21/(1-0.21)) = 2.305
d) 95% CI for RR is = 1.809 + 1.96 * ?/sqrt n = 1.816
= 1.809 - 1.96 * ?/sqrt n = 1.801
Thus the 95% confidence interval is 1.801< 1.809 < 1.816
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