Question

In a sample of 120 people in Finland, 26 (21.7%) were determined to have blood type B, while in a sample of 100 people in Norway, 12 (12%) of people were determined to have blood type B. Using the following R output, interpret the confidence interval, in terms of the biological question of interest.

       2-sample test for equality of proportions with continuity correction

data: c(26, 12) out of c(120, 100)
X-squared = 2.9226, df = 1, p-value = 0.08735
alternative hypothesis: two.sided
90 percent confidence interval:
0.005746442 0.187586892
sample estimates:
   prop 1    prop 2
0.2166667 0.1200000

Answer 1

The 90 percent confidence interval is given as

(0.005746442 , 0.187586892)

That means there is 90 percent chance that the confidence interval which has been calculated contains the true population mean. That is, 90% of the time, when we calculate a confidence interval, the true mean will be between 0.005746442 and 0.187586892.

10% of the time it will not. Because the true mean (Population mean) is an unknown value, we do not know if we are in the 10% or 90%.

We are 90% confident that the people were determined to have blood type B for Finland and Norway is between 0.005746442 and 0.187586892.