If you were told that a sample of 26 breast-fed infants had a mean hemoglobin le

Question

If you were told that a sample of 26 breast-fed infants had a mean hemoglobin level of x-bar = 13.9 grams/100 ml with a standard deviation of s = 1.7 g/100ml, give 95% confidence intervals for the mean hemoglobin level of breast-fed infants as indicated below.

a. Calculate the 95% confidence interval assuming that the standard deviation () of the breast-fed infants population (normal distribution) is = 2.1g/100ml.

b. Calculate the 95% confidence interval assuming that the standard deviation () of the breast-fed infants population is unknown.

Explanation / Answer

Here t table value is 2.060 for 25 df

a. Here sigma=2.1

So Margin of Error=E=(sigma*t)sqrt(n)=(2.1*2.060)/sqrt(26)=0.8484

Hence CI=mean+-E=13.9+-0.8484=(13.0516,14.7484)

b. Here sigma=s=1.7

So E=(1.7*2.060 )/sqrt(26)=0.6868

Hence CI=13.9+/-0.6868=(13.2132,14.5868)

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