Title: 10 Things to know about Confidence Intervals – MeasuringU
Headings: 10 Things to know about Confidence Intervals
10 Things to know about Confidence Intervals
Content: Confidence intervals don’t tell you the likely range of all values, just how much the average value is likely to fluctuate. Confidence intervals provide both the location and precision of a measure: For example, the graphs below show the 95% confidence intervals around the average System Usability Scale (SUS) score. The only difference between the graphs is the sample size. Even though they both show the same location (a mean score of 83), the one on the right has a larger sample size (60), making it a more precise estimate of the population SUS score than the sample with only 12. Three things impact the width of a confidence interval
Confidence level: This is the 95% part of the 95% confidence interval and also typically takes values of 90%, 99%, 80% and 85%. Confidence levels are the “advertised coverage” of a confidence interval. If we were to sample from the same user population 100 times, we’d expect the average to fall within the interval 95, 90 etc., times out of 100.