SATAdvanced (700+)Frequency: 1 - 2 questions
Margin of Error & Confidence Intervals
Margin of error accounts for random sampling variability. To decrease margin of error, you must INCREASE sample size (n). The margin of error applies ONLY to the population from which the random sample was drawn, not to subgroups or different populations.
Core Formula & Concept Cheat Sheet
1Margin of error ∝ 1 / √n (Larger sample size reduces margin of error)
2Confidence interval = Sample estimate ± Margin of error
3Results generalize ONLY to the sampled population.
The 700+ Score Trap
Assuming that a larger total population size changes margin of error (it does not; only the SAMPLE size matters).
Test Your Mastery
Official Exam FormatLive Interactive Practice Drill
A random sample of 600 likely voters in an election revealed that 52% plan to vote for Candidate X, with an associated margin of error of 4%. Which statement is the most appropriate conclusion?
Frequently Asked Questions
Does doubling the sample size cut margin of error in half?
No! Because margin of error is proportional to 1/√n, you must quadruple (4x) sample size to halve the margin of error.