Adjusted Ranking Metric (ARM)
Accounting for Differences in Exposure
What is the ARM?
- The Adjusted Ranking Metric (ARM) is a new measure available for Acute Care Hospitals (ACHs).
- The ARM accounts for differences in volume of exposure (specifically denominator) between facilities and is preferable for ranking facilities.
- Annual, facility-specific Reliability-Adjusted Rankings based on the ARM are displayed as percentiles on the Reliability-Adjusted Ranking dashboard within NHSN.
- Reliability-Adjusted Rankings for CLABSI, CAUTI, MRSA, CDI, SSI-COLO and SSI-HYST will be displayed only for acute care hospitals at this time.
How is the ARM different from the SIR?
The ARM provides complimentary information to NHSN’s primary summary measure, the Standardized Infection Ratio (SIR). The ARM and SIR are separate measures that serve different purposes in HAI analysis.
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Methods
The ARM is calculated as a ratio of numerator divided by denominator, where the ARM denominator is identical to that of the SIR. Explicitly, the ARM is the reliability-adjusted number of events divided by the risk-adjusted predicted number of events, whereas, the SIR is the number of events divided by the risk-adjusted predicted number of events.
ARM
SIR
ARM
SIR
Reliability-Adjustment
The type of reliability-adjustment incorporated into the ARM relies on methodological concepts dating back to 1977, and more specifically, has been used in CMS performance measurement since 2007 (for instance hospital 30-day mortality following acute myocardial infarction). Furthermore, the need for reliability-adjustment in assessing hospital performance has been recommended in a white paper published by a Committee of Presidents of Statistical Societies commissioned and published by CMS.
Statistical Issues In Assessing Hospital Performance pdf icon[PDF – 700 KB]external icon
Calculation of ARM Scores
NHSN calculates ARM scores from all acute care hospitals for six HAIs (CLABSI, CAUTI, MRSA, CDI, SSI-COLO, SSI-HYST). Individual hospitals are ranked against all other acute care hospitals for the same year. The ARM is presented as a percentile, called the Reliability-Adjusted Ranking and is available to hospitals within the NHSN application.
Facilities with No ARM Score
Facilities predicted to have fewer than one event in five years (based on the expected number of events for that HAI) are currently not given an ARM for that HAI because this suggests that the facility should have zero events in the current year. Instead, the number of events for that year is shown.
Implementation
Beginning in December 2019, the “Reliability-Adjusted Ranking” dashboard will be available for ACHs. The new dashboard is accessible underneath the existing “TAP Strategy Dashboard” on the NHSN home page in the NHSN Application.
This initial release will include data for 2018, with additional years added in future releases. Reliability-adjusted rankings for six HAIs (CLABSI, CAUTI, MRSA, CDI, SSI-COLO, SSI-HYST) will be displayed in a bar graph (example below). During this initial release, the rankings are available for use by ACHs only and are not made available to groups within NHSN, nor used by CMS pay-for-reporting or pay-for- performance programs.
ACHs are encouraged to review their reliability-adjusted rankings.
For more information, please contact NHSN@cdc.gov.
