Title: Confidence Interval (CI)
Headings: Confidence Interval
Confidence Interval
Sample Size
Point Estimate
CI = POINT ESTIMATE +/- (Reliability Factor) (Standard Error)
Confidence Interval for the MEAN
= sample mean +/- (confidence factor) (measure of variability)
Confidence Interval MEAN with KNOWN σ
EXAMPLE:
What does this tell us?
Confidence Interval MEAN with UNKNOWN σ
EXAMPLE:
What does this tell us?
Excel - Confidence Interval for MEAN
Confidence Interval for the STANDARD DEVIATION
Confidence Interval for PROPORTIONS
Confidence Interval for CAPABILITY
Confidence Interval Download
Confidence Interval Roadmap
Asymmetric Confidence Interval
Relationship with Margin of Error (ME)

Content: Most common confidence interval selections are 90%, 95%, or 99% but are dependent on the voice of the customer, your company, project, and other factors. Sample statistics such as the mean, standard deviation and proportion (x-bar, s, p-bar) are only estimates of the population parameters. Confidence Intervals are used to quantify the uncertainty by providing a lower limit and upper limit that represent a range of values that will represent the true population parameter with a specified level of confidence. Selecting a 99% CI suggests that approximately 99 out of 100 CI's will contain the population parameter. A 0.99 confidence interval states that there is 99% probability that the interval contains the population parameter, and that there is a 1.0% risk that the population parameter is not contained within the interval. Confidence Interval = CI = 1 - alpha risk
(1 - alpha-risk) is called the probability content or level of confidence. Alpha-risk is known as the significance level; the probability of being making an incorrect decision, in other words, being wrong. A specified value of the CI signifies that probability of the interval containing the population parameter, and that there is an alpha-risk (1-CI) that the population parameter is not contained within the interval. CI's are applied in statistical test for means, standard deviations, proportions, capability indices, regression analysis, and upper/lower control limits on control charts.