Case Mix Data

 Case Mix
Release and File Extract Status
(as of 7/08/2024)


Case Mix Overview

Case Mix Overview
(Updated December 2019)

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Case Mix Documentation 

Hospital Inpatient Discharge Database (HIDD)

Emergency Department Database (EDD)

Outpatient Observation Database (OOD)


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Information for Data Submitters


New! FY23 Hospital Inpatient Discharge Database (HIDD) Database

The Massachusetts Acute Hospital Case Mix Database is a database comprised of:

  • Hospital Inpatient Discharge Database (HIDD)
  • Emergency Department Database (EDD)
  • Outpatient Observation Database (OOD)


The Case Mix data includes detailed information on inpatient discharges, emergency department visits and observation stays. For each of these patient encounter types, hospitals submit detailed information, including: patient demographics, admission and discharge information, diagnostic and procedural coding, provider details and detailed charge information.

For comprehensive documentation on these data sets, please see the documentation manuals.

Government agencies, health care providers, payers, and researchers use CHIA's Case Mix databases for a wide variety of projects, including: public health initiatives, preventable hospitalizations, hospital market analysis, alternative care settings, and comparative costs and outcomes in acute care hospitals. To learn more about how Case Mix databases are used, view applications for data submitted by researchers and other entities. You can also review samples of both internal and external research using MA APCD and Case Mix data.


Annual Release Overview

CHIA’s Case Mix annual releases include one year’s worth of hospital data submissions. The annual release process includes:

  • Data Intake and Internal Processing
    CHIA works with approximately 70 Massachusetts hospitals throughout the year to ensure valid, high quality quarterly data submissions. Hospitals are required to deliver their submission files within 75 days after the end of each quarter. CHIA runs each file through a series of file- and field-level edits to confirm formatting and to check for data quality issues. CHIA has a strict limit on errors, expecting the files to be 99% error-free. CHIA notifies providers if their file(s) do not pass these intake edits and requires resubmissions.

  • Release Creation
    To prepare each annual release, CHIA compiles the four quarters of data submissions and completes a four week quality assurance validation process with the providers to test the completeness and quality of select fields. If data submission fixes are required, hospitals spend time fixing, validating and resubmitting data files. Following receipt of all files, CHIA loads the data into the Case Mix Data Warehouse and performs a series of steps including data cleaning and creation of derived fields. Release creation can take from eight to twelve weeks depending on whether we identify issues during testing.

  • Data Quality and Release Assurance Testing
    CHIA’s quality assurance team performs an eight to ten week quality assurance validation process to test the completeness and quality of select fields as well as any new product features and enhancements. If updates are required as a result of testing, CHIA performs comprehensive regression testing. After completing quality assurance testing, CHIA’s release assurance team validates the data creation process and ensures data completeness and accuracy. We then extract the most recent data to create the annual Case Mix Release Data Mart, which becomes the source for all data extracts.

  • Delivery of Data Extracts
    CHIA extracts data from the Case Mix Release Data Mart to create extract files for its customers. It can take from five to seven days to create an extract file. CHIA prioritizes delivery of extracts to Commonwealth agencies doing research in support of healthcare policy. Second priority is given to organizations that submit data. Third priority goes to independent researchers.