Sample Size
B. Sample Size
In October 2012, Environics Research asked Albertans which political party they would support and then published the following table and statement.
The report also included the number of people in each group within the sample and the margin of error for each group.
Can you see a relationship between the sample sizes and the margins of error?
There is a connection between the sample size and confidence interval for a particular confidence level. The Confidence Interval applet will allow you to explore the relationships further.
Open the Confidence Interval applet (14 March 2013, Created with GeoGebra) and use it to answer the following:
- How does the confidence interval change when the sample size is increased? Decreased?
- Which affects the confidence interval more, changing the sample size from 10 to 20 or from 90 to 100?
- How are the confidence level and confidence interval related?
- Many studies use a sample size of near 1000 and a confidence level of 95%. If a sample size of 100 was used instead, what confidence level must be used to give the same size of confidence interval?
Move the sliders to see how a confidence interval is affected by different parameters. Fine adjustments to the sliders can be made using the left and right arrow keys.
Please note that confidence intervals can be calculated various ways depending on available information; this applet uses a t-distribution.