If a CLABSI SIR is 2 with p-value 0.01 and a confidence interval of 2.1-4, how should the IP interpret this data?

• A. SIR is better than the benchmark.
• B. SIR is worse than the benchmark.
• C. CI includes 1, implying no difference.
• D. Null hypothesis cannot be rejected.

Answer: (B)

A standardized infection ratio above 1 means more infections than expected. A SIR of 2 indicates observed infections are twice what the benchmark would predict. The confidence interval from 2.1 to 4 stays entirely above 1, which means we are 95% confident the true SIR is above the benchmark, not crossing the no-difference point. The p-value of 0.01 reinforces this, showing there’s only a 1% chance of seeing such a difference if the true rate were equal to the benchmark. Put together, these results show a statistically significant excess of infections, i.e., the rate is worse than the benchmark. The alternative that there’s no difference isn’t supported, since the interval excludes 1 and the p-value is well below the typical 0.05 threshold.