Question

The birth weights for two groups of babies were compared in a study. In one group the mothers took a zinc supplement during pregnancy. In another group, the mothers took a placebo. A sample of 128 babies in the zinc group had a mean birth weight of 3456 grams. A sample of 142 babies in the placebo group had a mean birth weight of 3358 grams. Assume that the population standard deviation for the zinc group is 748 grams, while the population standard deviation for the placebo group is 660 grams. Determine the 90% confidence interval for the true difference between the mean birth weights for "zinc" babies versus "placebo" babies.

Step 1 of 2: Find the critical value that should be used in constructing the confidence interval.

Step 2 of 2: Construct the 90% confidence interval. Round your answers to the nearest whole number.

Answer 1

Given that,

For zinc group :

For placebo group :

Step 1) A 90% confidence level has significance level of 0.10 and

=> Critical value = 1.645

step 2) The 90% confidence interval for (μ1 - μ2) is,

Therefore, required confidence interval is (-44, 240)