Confidence Interval Estimation - Discussion
When the results of a survey or poll are published, the sample size and the margin of error are both given. For example: 1000 voters were surveyed and 39±2% of the voters agree with the president. In this example N=1000 and the margin of error (MoE) is 2%.
This website lists several public opinion polls. Search the site and find a poll where the sample size and margin of error are given. Try to find a poll dealing with a topic in your profession or one in which you are really interested.
http://www.pollingreport.com
Determine the following information for the selected poll results and include in your initial post:
- URL for the website. State the poll question, the sample size N, and the margin of error (also known as sampling error).
- Interpret the results of your poll using your own words and full sentences. Note: Depending on the question asked, your poll may have more than one poll result - you only need to discuss one result.
- State the confidence interval using the MoE. What does this confidence interval estimate?
- Use this worksheet ( click to download CIE Proportion.xlsx ) to calculate the confidence interval based on the sample size and the number of successes (the proportion you are interested in). Use a confidence level of 95%.
- What is the calculated confidence interval? How does this compare to the interval in part 3 using the poll's MoE?
- Discuss potential biases that could skew sampling results.