# confidence interval

• December 14th 2009, 11:29 PM
superman31
confidence interval
A principal randomly slected 6 students to take an aptitude test, their scores were 83, 84.1, 83.5, 83.7, 84.1, and 73.5. construct a 90% confidence interval for the mean score for all students. Assume the population has a normal distribution.
• December 15th 2009, 04:16 AM
CaptainBlack
Quote:

Originally Posted by superman31
A principal randomly slected 6 students to take an aptitude test, their scores were 83, 84.1, 83.5, 83.7, 84.1, and 73.5. construct a 90% confidence interval for the mean score for all students. Assume the population has a normal distribution.

Compute the sample mean $m$ and the unbiased estimate from the sample of the population SD $s$.

Then the interval you require is: $(m-\lambda s, m+\lambda s)$ where $\lambda$ is the $95 \%$ point for the cumulative t-distribution with $n=5$ degrees of freedom.

CB