Confidence Interval for Baby Birth Weight Data

In this activity, you will be calculating the 95% confidence interval for the baby birth weight data set.  The data was collected from 44 babies born in a 24-hour period at the Mater Mothers' Hospital in Brisbane, Queensland, Australia on December 18, 1997.  The birth weight of the babies is in grams.

Using data set in Excel, determine the mean and the standard deviation for the baby birth weight data set. Using these two values, then calculate the 95% confidence interval for the baby birth weight data. Recall that the t-value that corresponds to 95% is 1.96. Record the confidence interval as the sample mean plus or minus the appropriate multiple of the standard error of the mean.

Answer the following questions on the same page as your Excel data, put your name and period in a header (flush right), and print the document sized to one page.

1. What is the mean?
2. What is the standard deviation?
3. What is the 95% confidence interval?
4. Would the confidence interval become wider or more narrow if the confidence level was raised to 99.7%?
5. Would the confidence interval become wider or more narrow if the sample size was doubled?
6. Why would doubling the sample size have the effect noted in question 5?

Original work on this document was done by Central Virginia Governor's School students Jennifer Rice, Eliza Evans, and Chris Earle (Class of '03).

Copyright © 2011 Central Virginia Governor's School for Science and Technology, Lynchburg, VA