Did I Get This – Confidence Intervals – Proportions #3

Published: February 16th, 2013

Category: Activity 2: Did I Get This?

The purpose of this activity is to use statistical software for calculating the sample proportion. 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 proportion using software.

Background: The U.S. federal ban on assault weapons expired in September 2004, which meant that after 10 years (since the ban was instituted in 1994) there were certain types of guns that could be manufactured legally again. A poll asked a random sample of 1,200 eligible voters (among other questions) whether they were satisfied with the fact that the law had expired. The datafile linked below contains the results of this poll (Data were generated based on a poll conducted by NBC news/Wall Street Journal Poll). We would like to estimate p, the proportion of U.S. eligible voters who were satisfied with the expiration of the law, with a 95% confidence interval.

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

If you prefer to skip this process and just answer the questions, you can reveal the value needed to continue.

This document is linked from Population Proportions.