Did I Get This – Confidence Intervals: Means #3

Published: February 16th, 2013

Category: Activity 2: Did I Get This?

Here is one final practice for these confidence intervals!!

The purpose of this activity is to use statistical software for calculating the sample mean. Software is particularly useful when all you have are the raw data (no summary has been calculated), which is what you encounter in practice. In all the examples and activities we looked at so far, the sample mean is given (rather than the whole data set), in which case it will often take you less time to calculate the confidence interval by hand than to launch a software program and ask it to do the calculation for you. To answer these questions, you will need to recall how to find the sample mean using software.

Background: Some studies suggest that women having their first baby at age 35 or older are at increased risk of having a baby with a low birth weight. A medical researcher wanted to estimate μ (mu), the mean weight of newborns who are the first child for women over the age of 35. To this end, the researcher chose a random sample of 125 women age 35 or older who were pregnant with their first child and followed them through the pregnancy. The datafile linked below contains the birth weight (in grams) of the 125 newborns (women pregnant with more than one child were excluded from the study). From past research, it is assumed that the weight of newborns has a standard deviation of σ = sigma = 500 grams. We will estimate μ (mu) with a 99% confidence interval.

The dataset is available in Excel format (birthweight.xls) and in CSV format (birthweight.csv).

If you prefer to skip this process and just answer the questions, you can reveal the sample mean for this data.


This document is linked from Population Means (Part 3).