In 2020, CMS contracted an expert panel to validate the 27 CCW Chronic Conditions algorithms following the change from International Classification of Diseases (ICD)-9 to ICD-10-CM. CMS also asked the expert panel to refine these algorithms and identify additional conditions to add to the CCW, resulting in the 30 CCW Chronic Conditions algorithms.

The objectives of this document are to: 1) provide a high-level description of the condition definition and algorithm differences between the 27 CCW Chronic Conditions and the 30 CCW Chronic Conditions, 2) compare the prevalence of the 27 CCW Chronic Conditions to the prevalence of the 30 CCW Chronic Conditions in the Medicare fee-for-service (FFS) data, 3) identify the impact of the updated condition definitions on the first occurrence dates (also referred to as “ever” dates), and 4) discuss implications for researchers in terms of switching to the 30 CCW Chronic Conditions file.

On October 1, 2015, CMS converted from the International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM) to the 10th Revision, Clinical Modification (ICD-10-CM) and Procedure Coding System (ICD-10-PCS).

The objectives of this document are to: 1) verify that the CCW received Medicare claims after the ICD-10 conversion without disruption and demonstrate the impact on claims volume in the initial months of the conversion and 2) evaluate the impact of the conversion from ICD-9 to ICD-10 codes on prevalence estimates for the CCW condition algorithms.

As of May 2017, the Master Beneficiary Summary File (MBSF) includes Medicare enrollment information from the CMS Common Medicare Environment (CME) rather than the CMS Enrollment Database (EDB). The CME improves the identification of Medicare Part B enrollment and also allows for more timely release of the MBSF.

While investigating the accuracy of the MBSF, CMS discovered that under rare sets of circumstances, there were changes to a beneficiary's enrollment record that were not reflected in the monthly EDB loads to the CCW. There were times when an enrollment record in the CCW EDB should have been marked as no longer current, but was mistakenly retained as a current record (i.e., enrollment record should have been marked as no longer active for certain months - and this did not occur).

Medicare administrative claims data are useful for monitoring service utilization – including hospitalizations, home health and physician office visits. Claims generally take many months to be considered ‘final' – and be mature enough that the data produce stable estimates of service use, reasons for service, and payments. However, timely information allows investigators to monitor the progress of programs and interventions, enabling mid-course adjustments to improve results.

The objective of this document is to describe the completeness of Medicare Institutional fee-for-service (FFS) claims, Medicare Non-Institutional FFS claims, and Part D Events (PDEs) at different levels of claims maturity (i.e., after different amounts of time have elapsed from the service date to the claim processing date).


This overview provides background information and considerations for users of the Chronic Conditions Warehouse's (CCW) Medicaid data. In this paper, we provide an overview of the characteristics of Medicaid, highlighting important points for researchers interested in cross-State or within-State comparisons. We describe some of the major types of variation across the States and provide topics for researchers to consider when designing studies using Medicaid data in general, and the CCW data in particular.

Previous studies have found that Medicaid enrollees have higher rates of emergency department (ED) utilization compared to Medicare, private insurance and uninsured populations. In an effort to provide a more comprehensive and nuanced understanding of ED utilization in Medicaid, we explore utilization patterns for different subpopulations of Medicaid.

In this report macro validation is used as a strategy to validate encounter data from the Chronic Conditions Warehouse (CCW). Metrics were calculated from the data and used to measure completeness across states and Medicaid populations.

The purpose of this data brief is to provide researchers with information on how to use the Centers for Medicare & Medicaid Services' (CMS) Chronic Conditions Warehouse (CCW) to analyze Medicaid long-term services and supports populations and their service utilization.

The purpose of this data brief is to illustrate how researchers and policymakers can use data from the Centers for Medicare & Medicaid Services' Chronic Conditions Warehouse (CCW) to assess Medicaid enrollees' utilization of ambulatory services.