Guided Notes

Comparing Groups: Rates, Confidence & Significance

Compare rates between clinics, time periods and populations — confidence intervals for proportions, chance variation, statistical vs practical significance, and common traps.

Every rate has uncertainty

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If a clinic's readmission rate is 18% from 50 discharges, the 'true' long-run rate could plausibly be quite different — 9 vs 10 readmissions changes it by 2 points. A 95% confidence interval (CI) shows the plausible range. For a proportion p with n cases (normal approximation): CI = p ± 1.96 × √(p(1−p)/n) Example: 18% of 50 → ±10.6 points → 7.4% to 28.6%.