Why this chapter matters
Confidence intervals report plausible ranges for unknown population values, which is often more informative than a single estimate.
What you will learn
- Build one-sample confidence intervals for means and proportions under stated conditions.
- Interpret interval meaning correctly in repeated-sampling terms.
- Analyze how confidence level and sample size affect margin of error.
Lessons in this chapter
- Point estimates and margin of errorSeparate center estimate from uncertainty width.
- Intervals for meansConstruct and read t-based intervals when population spread is unknown.
- Intervals for proportionsConstruct and interpret one-proportion confidence intervals.
- Choosing confidence and sample sizeUse design goals to balance precision and certainty. Read the full guide →
Study task
Design a poll for a binary opinion question with target margin of error 3 percentage points at 95% confidence, and explain your sample size logic.
Chapter checkpoint
What changes first if you increase confidence level from 90% to 99% with the same data?
The critical value increases, so margin of error increases and the interval becomes wider.