🟢 Stats: Confidence Intervals — What They Really Mean

z-values: 90% → 1.645, 95% → 1.96, 99% → 2.576

What 95% CI means: "If we repeated this experiment 100 times, about 95 of the resulting intervals would contain the true population parameter."

What it does NOT mean: "There's a 95% probability the true value is in this interval." The true value is fixed — it either is or isn't. The confidence is about the procedure.

For proportions: CI = p̂ ± z × √[p̂(1-p̂)/n]