Explanation of Star Ratings

For STS Congenital Heart Surgery Database (CHSD) participants, the star rating is based on the overall risk-adjusted observed-to-expected (O/E) operative morality ratio for all patients undergoing pediatric and/or congenital cardiac surgery, using the STS CHSD Mortality Risk Model.

Operative mortality is defined as (1) all deaths occurring during the hospitalization in which the procedure was performed, even after 30 days (including patients transferred to other acute care facilities), and (2) those deaths occurring after discharge from the hospital, but within 30 days of the procedure.

The three categories of ratings are based on a participant’s overall risk-adjusted O/E operative morality ratio:

  • One star: higher than expected operative mortality; the 95% confidence interval (CI) for a participant’s risk-adjusted O/E mortality ratio was entirely above the number 1.
  • Two stars: as expected operative mortality; the 95% CI for a participant’s risk-adjusted O/E mortality ratio overlapped with the number 1.
  • Three stars: lower than expected operative mortality; the 95% CI for a participant’s risk-adjusted O/E mortality ratio was entirely below the number 1.

Examples of star ratings and 95% CI

Overall
Star Rating
Description Examples of
O/E (95% CI)
One Star Lower and upper
limits of CI > 1.0
1.2 (1.1, 1.4)
Two Stars CI includes 1.0 0.8 (0.7, 1.0)
Three Stars Lower and upper
limits of CI < 1.0
0.6 (0.2, 0.9)

In addition to the overall star rating, congenital heart surgery public reporting includes the overall operative mortality rate over a 4-year period for patients of all ages, as well as the operative mortality rate in each of the five Society of Thoracic Surgeons - European Association for Cardio-Thoracic Surgery Congenital Heart Surgery Mortality Categories (STAT Mortality Categories)

STAT Mortality Categories are a multi-institutional, validated complexity stratification tool for pediatric and congenital heart surgery. Operations were sorted by increasing risk and grouped into 5 categories (the STAT Mortality Categories). STAT Category 1 is associated with the lowest risk of mortality and STAT Category 5 is associated with the highest risk of mortality. The STAT Mortality Categories allow outcomes to be assessed in relation to the complexity of the operations being performed. 

The components include:

#/Eligible — a fraction with the numerator representing the number of observed patient deaths and the denominator representing the number of patients included in the calculation of operative mortality

Observed —the observed operative mortality rate as a percentage. This percentage is calculated by dividing the number of observed deaths by the number of eligible patients included in the calculation.

Expected — the expected operative mortality rate as a percentage. The 2014 STS CHSD mortality risk model is used to estimate the number of expected patient deaths when considering the unique case mix of an STS CHSD participant or the mix of patients treated as defined by all of the variables listed in the above table.

O/E (95% CI) — the observed-to-expected (O/E) ratio is the number of observed deaths divided by the number of expected deaths. An O/E ratio greater than 1 means that the STS CHSD Participant had more deaths than expected based on the actual case mix of that STS CHSD participant. An O/E ratio of less than 1 means that the STS CHSD participant had fewer deaths than expected based on the actual case mix. Small differences in the O/E ratio are usually not statistically significant, which is why the O/E ratio is reported along with 95% confidence intervals (CIs).

The 95% CIs provide a range of O/E ratios that could represent a STS CHSD participant’s underlying true O/E ratio, which is the ratio that would be observed hypothetically if the STS CHSD participant operated on a very large number of patients. If the CI is very wide, it means that the O/E ratio is a less exact estimate of the true underlying O/E ratio of the STS CHSD participant. In general, the width of the CI decreases as the number of patients included in the calculation increases.

Adjusted Rate (95% CI) — the adjusted mortality rate (AMR) is an estimate (based on a statistical model) of what the hospital’s mortality rate would be if its observed performance was extrapolated to the overall STS case mix (specifically, the mix of age, weight, procedure types, and other model-specific variables including prior cardiothoracic operations, non-cardiac congenital anatomic abnormalities, chromosomal abnormalities, syndromes, and preoperative risk factors). It is calculated by the following formula: AMR of hospital = O/E ratio of hospital x overall observed STS mortality rate.

The 95% CIs provide a range of mortality rates that could represent the underlying true adjusted operative mortality rate of a given STS CHSD participant, which is the rate that would be observed hypothetically if the STS CHSD participant operated on a very large number of patients. If the CI is very wide, it means that the adjusted operative mortality rate of the STS CHSD participant is a less exact estimate of its true underlying adjusted operative mortality rate. In general, the width of the confidence interval decreases as the number of patients included in the calculation increases.