A *confidence interval* is a specific interval estimate of a parameter determined by using data obtained from a sample.

Concept #1: The percentage in a *confidence interval* represents the level of certainty that we have for the mean lying within a given range.

Example #1: Construct a 95% confidence interval for an experiment that found the mean temperature for a given city in July as 103.5 ** ^{o}**C with a standard deviation of 1.8 from 10 measurements.

Example #2: The barium content of a metal ore was analyzed several times by a percent composition process.

**0.010 0.011 0.004 0.011**

Calculate the mean, median and mode.

Example #3: From EXAMPLE 1, calculate the standard deviation.

Practice: From the examples given above, find the 90% confidence interval.