Public reporting for the STS Congenital Heart Surgery Database (CHSD) presents hospitalspecific results over a 4year period.
Definitions and Explanation of CHSD Outcomes
Operative mortality (patient death) is defined as a death that occurs:

During the hospital stay in which the procedure was performed, no matter how long the patient remains in the hospital after the operation;

At another hospital because the patient is transferred but is never discharged; OR

Within 30 days of the operation even if the patient is discharged home.
The mortality rate (death rate) is calculated by dividing the number of deaths by the total number of patients undergoing surgery.
A hospital's case mix takes into account many different patient factors such as age, weight, procedure types, and existing health conditions (e.g., prior heart operations, noncardiac congenital abnormalities, chromosomal abnormalities, syndromes, and preoperative risk factors). Some hospitals may treat more patients with more complicated and higherrisk conditions than other hospitals and, therefore, operate on patients with a lower chance of survival.
Note: If Hospital A has a lower mortality rate than Hospital B, it does not necessarily mean that Hospital A is better; it could indicate that Hospital B treated patients with more severe problems.
To account for differences in case mix, a statistical method known as risk adjustment is used to analyze results in a way that incorporates how sick the patients were before treatment. The STS CHSD Mortality Risk Model may be found online here.
An STS Public Reporting page for a CHSD participant hospital shows the hospital's operative mortality (patient death) as an overall rate and by STAT Mortality Category over a 4year period.

Overall  This rate includes patients of all ages, diagnoses, and procedures. It takes into account additional factors such as patient age, the presence or absence of genetic abnormalities, syndromes, and noncardiac anomalies (e.g., airway or kidney anomalies), and the condition of patient going into the operation.

STAT Mortality Categories 15  Congenital heart operations are grouped by the complexity of the procedure in what is known as STAT Categories. STAT Category 1 includes the least complex operations, which are associated with the lowest risk of mortality STAT Category 5 includes the most complex operations, which are associated with the highest risk of mortality. Examples include:
STAT Category 1: Patch repair of Atrial Septal Defect (ASD) or Ventricular Septal Defect (VSD) pulmonic valve replacement
STAT Category 2: Ross procedure, Fontan procedure, tricuspid valve repair
STAT Category 3: Complete AV Canal (AVC) repair, Arterial Switch Operation (ASO), lung transplant
STAT Category 4: BlalockTaussig (BT) shunt, heart transplant, truncus arteriosus repair
STAT Category 5: Heart and lung transplant, Norwood procedure, truncus plus interrupted arch repair
How to Read the Outcomes Data Table
Population 

Neonates (0  30 days)

Infants (31 days  1 year)

Children (>1 year  <18 years)

Adults (18 years and older) with congenital heart disease
#Eligible = Actual number of patient deaths ÷ Actual total numbers of patients included in the calculation of operative mortality
Observed  the actual observed operative mortality rate. This is a percentage that is calculated by dividing the number of deaths by the number of eligible patients included in the calculation for each STAT Category.
Expected  a statistical formula is used to estimate the number of expected patient deaths when considering the unique case mix of a hospital participating in the CHSD.
O/E Ratio  the observedtoexpected (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 hospital had more deaths than expected based on the actual case mix of that hospital. An O/E ratio of less than 1 means that the hospital had fewer deaths than expected based on the actual types of cases treated at that hospital.
Confidence Interval (CI)  because each hospital's mortality rate varies, CIs provide predicted range of O/E ratios (the numbers in parentheses) that could represent a hospital's underlying true O/E ratio. If the spread of the CI numbers is really wide, it means that the O/E ratio is a less exact estimate of the true underlying O/E ratio. In general, the width of the CI decreases as the number of patients included in the calculation increases.
If the numbers in the 95% CI (numbers in parentheses) for a participant hospital's O/E ratio:

Are greater than 1, then the hospital has higher than expected mortality, which indicates lower than expected performance

Overlap with the number 1, then the hospital is performing as expected

Are less than 1, then the hospital has lower than expected mortality, which indicates higher than expected performance
Adjusted Rate (Adj. Rate)  an estimate of what the hospital's mortality rate would be if its observed performance was applied to the overall case mix included in the CHSD. The formula is:
Adj. Rate = O/E ratio of a hospital x the overall observed mortality rate for all hospitals in the CHSD
Access CHSD Public Reporting results