CMS Hospital Quality & Patient-Outcome Metrics (Care Compare)

CMS hospital quality and patient-outcome metrics are the publicly reported performance measures behind Medicare’s Care Compare (formerly Hospital Compare): risk-adjusted mortality and readmission rates, complication rates, healthcare-associated infections, timely/effective-care process measures, and HCAHPS patient-satisfaction survey results, reported per hospital. The data is free and public. Used in, for example, Lewellen, where CMS patient-outcome metrics (mortality, readmissions, patient satisfaction) are nonfinancial hospital-performance proxies in supplementary tests.

• Cost: free, public.
• API key: none required.
• Coverage: all Medicare-certified hospitals (~4,000-5,000 facilities); many measures published from 2008-2009 onward, refreshed roughly quarterly.
• Home: https://data.cms.gov/provider-data/

Access

The Provider Data Catalog exposes a DKAN/metastore API. List datasets, then pull a dataset’s CSV distribution. No authentication:

# 1. List all provider-data datasets (titles + identifiers)
curl -sL "https://data.cms.gov/provider-data/api/1/metastore/schemas/dataset/items?show-reference-ids=false"

# 2. Resolve one dataset's CSV download URL (e.g. Complications and Deaths - Hospital)
curl -sL "https://data.cms.gov/provider-data/api/1/metastore/schemas/dataset/items/ynj2-r877?show-reference-ids=true"

# 3. Download the CSV using the downloadURL from the step-2 response.
#    The resources/<hash>_<id>/ subdirectory is in that response and changes
#    each refresh, so read it from the API rather than hard-coding it:
curl -sL -o complications_deaths_hospital.csv \
  "https://data.cms.gov/provider-data/sites/default/files/resources/6af7c44d77436e5a1caac3ce39a83fe9_1777413950/Complications_and_Deaths-Hospital.csv"

Each measure family is published at three grains as separate datasets, suffixed - Hospital, - State, and - National (for example ynj2-r877 Complications and Deaths - Hospital, dgck-syfz Patient survey (HCAHPS) - Hospital, 77hc-ibv8 Healthcare Associated Infections - Hospital). A hospital row carries Facility ID (the CMS Certification Number, CCN), Measure ID, Score, Denominator, Lower Estimate, Higher Estimate, and a Compared to National flag.

Load in Python

import pandas as pd

df = pd.read_csv("complications_deaths_hospital.csv", dtype={"Facility ID": str})
# Long format: one row per (Facility ID, Measure ID). Pivot to a hospital panel:
wide = df.pivot_table(index="Facility ID", columns="Measure ID",
                      values="Score", aggfunc="first")

Gotchas (the ones that bite pipelines)

• Scores are risk-adjusted, not raw rates. Mortality, readmission, and complication measures are CMS risk-standardized rates (RSMR/RSRR), modeled to adjust for patient case mix. They are not raw counts divided by admissions, and the adjustment model changes over time. Do not compare a CMS risk-adjusted rate to a hand-computed raw rate as if they measure the same thing.
• Score is text with footnote codes, not always a number. Cells for suppressed or not-applicable measures hold footnote codes (for example “Not Available”, “Number of Cases Too Small”) rather than a value. Parse the companion footnote columns and coerce Score to numeric explicitly; a naive float() will choke or silently drop rows.
• Small-volume hospitals are suppressed. Measures are withheld when the denominator is below a threshold (commonly 25 cases). This censors small and rural hospitals non-randomly, so a sample of hospitals with non-missing scores is selected toward larger facilities. Account for this before treating missing as random.
• Measures and reporting periods change across refreshes. CMS adds, retires, and re-specifies measures, and each measure covers a rolling multi-year window (often three years of discharges) that is not the calendar year of the file. Two vintages can have different Measure ID sets and different underlying periods; pin the refresh date and read the measure’s data-collection window, do not assume the file year is the data year.
• Join key is the CCN, and it is a string. Facility ID is the 6-character CMS Certification Number. For the acute-care, critical-access, and psychiatric hospitals in Care Compare it is all digits with leading zeros (for example 140010), so read it as a string or the leading zeros are lost. It is not the NPI, not the AHA ID, and not an EIN; crosswalking to AHA or HCRIS requires the CCN explicitly.
• HCAHPS is survey-based and differently scaled. Patient-satisfaction (HCAHPS) measures are “top-box” percentages from a sampled survey with their own response-rate and mode adjustments, on a different scale from the clinical outcome measures. Do not pool HCAHPS percentages with risk-adjusted rates without rescaling.

Measure families (per-hospital datasets)

Family	Example dataset id	What it reports
Complications and Deaths	ynj2-r877	Risk-adjusted mortality and complication rates
Unplanned Hospital Visits	(readmissions)	Risk-adjusted readmission / return rates
Healthcare Associated Infections	77hc-ibv8	CLABSI, CAUTI, SSI, MRSA, C. diff
Patient survey (HCAHPS)	dgck-syfz	Patient-experience top-box percentages
Timely and Effective Care	(process)	Process-of-care / timeliness measures

(Each also has - State and - National siblings for the benchmark levels.)

Citation

Cite CMS, Care Compare / Provider Data Catalog, the dataset name and identifier, the refresh date, and the access date, for example: Centers for Medicare and Medicaid Services, Care Compare: Complications and Deaths - Hospital (data.cms.gov/provider-data, dataset ynj2-r877), accessed YYYY-MM-DD. Record the dataset identifier and refresh date, since measures and periods change between vintages.