Confidence Interval Calculator

Calculate and interpret confidence intervals for means, proportions, and other parameters. Covers z-intervals, t-intervals, and bootstrap methods with proper interpretation.

Usage

Provide your sample data and desired confidence level to get a confidence interval with interpretation.

Examples

• "Calculate a 95% confidence interval for a sample mean of 42 with SD 5 and n=30"
• "What sample size do I need for a margin of error of 3%?"
• "Explain what a confidence interval actually means"

Guidelines

• Use t-intervals for small samples or when population SD is unknown
• A 95% CI means 95% of such intervals would contain the true parameter
• Report the confidence level and sample size alongside the interval
• Wider intervals indicate more uncertainty, not less precision
• Consider bootstrap methods when parametric assumptions are not met