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Commit e940cbaa authored by Robert Ricci's avatar Robert Ricci

Fix the upper/lower bound problem in the final problem

parent 34a52b4e
......@@ -111,20 +111,20 @@ Part A: Graph the CIs
Part B: How many measurements does it take to get a difference at 90%
confidence?
Bottom end of 90% confidence interval for A:
Top end of 90% confidence interval for A:
mean(A) - (qnorm(.95)*sd(A))/sqrt(length(A))
mean(A) + (qnorm(.95)*sd(A))/sqrt(length(A))
Upper end of CI for B:
Bottom end of CI for B:
mean(B) + (qnorm(.95)*sd(B))/sqrt(length(B))
mean(B) - (qnorm(.95)*sd(B))/sqrt(length(B))
So, we need:
mean(A) - (qnorm(.95)*sd(A))/sqrt(n)) >= mean(B) + (qnorm(.95)*sd(B))/sqrt(n)
mean(A) + (qnorm(.95)*sd(A))/sqrt(n)) >= mean(B) - (qnorm(.95)*sd(B))/sqrt(n)
Which becomes:
((qnorm(.95)*(sd(A) + sd(B)))/(mean(A) + mean(B)))^2
n = ((qnorm(.95)*(sd(A) + sd(B)))/(mean(A) + mean(B)))^2
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