1. What degree of confidence should I use when constructing a confidence interval?
Usually in a question for an examination the required degree of confidence is given.
In situations involving important issues such as medical matters or large amounts of money it is better to be cautious and use high levels of confidence e.g. 99%. This provides a wider interval.
2. What do I use for constructing a confidence interval when the population standard deviation is not available?
Providing the sample size is large the standard deviation of the sample can be used.
Remember that when finding the standard deviation of a sample on a calculator the divisor (n − 1) is used.
