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Expert: - 2/13/2009


Question
Please answer the below mentioned question, as i m unable to find the answer of it anywhere.

A study of iron deficiency among infants compared samples of infants following different
feeding regimens. One group contained breast-fed infants, while the children in other group
were fed a standard baby formula without any iron supplements. Here are summary results
on blood hemoglobin levels at 12 months of age.

Group            n   mean   S
Breast-fed   23   13.3   1.7

Formula           19   12.4   1.8


a. Is there significant evidence that the mean hemoglobin level is higher among breastfed
babies? State null hypothesis and alternate hypothesis and conduct a t-test.
b. Give a 95% confidence interval for the mean difference in hemoglobin level between
the two populations of infants.


Answer
I would calculate the standard deviation on the entire set of
numbers.  I would then average the breast fed and the formula
groups separately.  Using the standard deviation, divide the
difference in the average by that number.  The would give you
how many standard deviations there are between the two.

Using a one-sided normal table, you can look up the number of standard deviations you have as a probability of getting this
difference.

a. The null hypothesis is that the mean globulin level is
higher among breast-fed babies.  The alternative hypothesis
is that there is that there is no difference.

b. Find a one side normal table and look up the probability.
In case you need a table, here it is.

http://www.math.unb.ca/~knight/utility/NormTble.htm

Also, 95% puts you at about 1.645 standard deviations.

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