Confidence Interval

Also known as: CI, Confidence Interval, Margin of Error, Error Range

Range of values within which the true population value is estimated to fall, with a 95% confidence level.

A Confidence Interval (CI) is a range of values calculated from sample data within which the true value of the population parameter (e.g., the real proportion of people preferring a brand) is estimated to fall, with a given probability (typically 95%).

For example: if 55% of respondents prefer Brand A, with a 95% CI of [51%, 59%], this means we have 95% confidence that the true preference percentage in the population is between 51% and 59%.

The confidence interval is more informative than the p-value alone because it shows both the estimated magnitude of the effect and its precision. In market research, CIs are fundamental for comparing groups and deciding whether observed differences are real or likely due to sampling chance.