Back to top
What is the CMS cell size suppression policy?

As outlined for researchers in the data use agreement (DUA), the CMS cell size suppression policy sets minimum thresholds for the display of CMS data. The policy stipulates that no cell (e.g. admissions, discharges, patients, services, etc.) containing a value of 1 to 10 can be reported directly. A value of zero does not violate the minimum cell size policy. In addition, no cell can be reported that allows a value of 1 to 10 to be derived from other reported cells or information. For example the use of percentages or other mathematical formulas that, in combination with other reported information, result in the display of a cell containing a value of 1 to 10 are prohibited. The cell suppression policy also applies to the reporting of excluded cases.

CMS standards for minimum cell sizes aim to protect the confidentiality of Medicare and Medicaid beneficiaries by avoiding the release of information that can be used to identify individual beneficiaries. The policy applies to any output in tables and texts describing any of the following: beneficiaries, procedures, and diagnoses. The CMS policy applies to the use of CMS research identifiable files (RIF) and limited data sets (LDS). Any documents (manuscript, table, chart, study, report, etc.) created using CMS data must adhere to the minimum cell sizes set forth in this policy.

How to avoid violating the CMS cell size suppression policy

There are several options that researchers can employ to comply with the minimum cell size requirements outlined in the CMS cell size suppression policy. Common strategies to avoid displaying a cell of 1 to 10 include collapsing cells, coarsening data, and cell suppression.

The remainder of this document presents three common scenarios that would violate the CMS cell size suppression policy and provides examples of strategies that can be undertaken to comply with the CMS cell size suppression policy.

  1. Table displays a cell with a value between 1 and 10
  2. Information from multiple tables can be used to derive values between 1 and 10
  3. Table displays a value for excluded patients that is between 1 and 10

 

Scenario 1

A value of 1 to 10, representing admissions, discharges, patients, services, etc., is directly displayed.

Table 1a violates the CMS cell suppression policy because the age category 85+ years displays a value of 6. 

Violates CMS policy: Displays cell value of 1 to 10
Beneficiary age group Procedure A (N=2,690), N (%)
60-69 years 1,900 (71)
70-74 years 400 (15)
75-79 years 290 (11)
80-84 years 94(3.5)
85+ years 6 (0.22)
Table 1a. Age Distribution of Patients with Procedure A
Does not violate CMS policy: Collapse data to achieve cell value 10
Beneficiary age group Procedure A (N=2,690), N (%)
60-69 years 1,900 (71)
70-74 years 400 (15)
75-79 years 290 (11)
80+ years 100 (3.7)
Table 1b. Age Distribution of Patients with Procedure A

Table 1b corrects the problem of the cell value for the 85+ age category by collapsing the age categories 80-84 years and 85+ years to achieve a displayed cell value that is greater than the CMS minimum threshold of 10.

Table 1c corrects the problem of the cell value for the 85+ age category by coarsening the data for 85+ years as well as for another age category:

  • Add the value that is between 1 and 10 to any of the other cell values, e.g. for the 60-69 years category: 1900 + 6 = 1906
  • Subtract 11 from the total for the 60-69 years category: 1906 -11 = 1895
  • Mask the 60-69 years category cell as > 1895 and the 85+ cell as <11.
Does not violate CMS policy: Coarsen data to prevent cell value of 1 to 10
Beneficiary age group Procedure A (N=2,690), N (%)
60-69 years >1,895 (>70.4)
70-74 years 400 (15)
75-79 years 290 (11)
80+ years
Table 1c. Age Distribution of Patients with Procedure A
Violates CMS policy: Insufficient suppression
Beneficiary age group Procedure A (N=2,690), N (%)
60-69 years 1,900 (71)
70-74 years 400 (15)
75-79 years 290 (11)
80-84 years 94 (3.5)
85+ years **
Table 1d. Age Distribution of Patients with Procedure A

Table 1d suppresses the cell that displayed a value of 1 to 10, but since the column total is known, the value for the age category 85+ can be derived [** = 2690 – (1900+400+290+94) = 6], which still violates the CMS policy.

Adequate suppression for the 85+ age category requires counter-suppression of another cell. In Table 1e, the age category with the next lowest value (80-84 years) is suppressed, but users can choose which other cell to suppress.

Does not violate CMS policy: Sufficient suppression
Beneficiary age group Procedure A (N=2,690), N (%)
60-69 years 1,900 (71)
70-74 years 400 (15)
75-79 years 290 (11)
80-84 years **
85+ years **
Table 1e. Age Distribution of Patients with Procedure A