|VisitLink - Visit linkage variable
|State Specific Notes
The VisitLink data element is one of two data elements that are supplemental information created for HCUP States for which there are encrypted person identifiers. The visit linkage variable (VisitLink) can be used in tandem with the timing variable (DaysToEvent) to study multiple hospital visits for the same patient across hospitals and time while adhering to strict privacy regulations. Maps indicating the availability of the revisit variables provide detailed information regarding which States release this information in the Central Distributor SID, SASD, and/or SEDD by year. VisitLink is derived from encrypted person numbers provided by the HCUP Partner. Partners sometimes change their coding scheme between data years, which in turn causes a discontinuity in VisitLink.
Please note that the values of VisitLink are unique within a State and data year, but not across States. For example, a unique value of VisitLink will track a patient within a State, such as the 2010 California SID, SASD, and SEDD, but the same value of VisitLink may be also be used for a different patient in another State, such as 2010 New York SID, SASD, and SEDD.
The patient's date of birth and gender were used to qualify the encrypted patient numbers provided to HCUP. A new verified person number (visitLink) was assigned for each unique combination of the qualifying information (encrypted person number, date of birth, and gender). Consider the following example: Five records have the same encrypted person numbers, but two records have one date of birth and gender, and the remaining three records have a different, but consistent, date of birth and gender. The two records with identical identifying information have one value of visitLink, and the other three records have a different value of visitLink.
No verified person number is assigned if any of the three pieces of information was missing (i.e., visitLink is missing). Additionally, no verified person number is assigned if there were more than 40 hospital visits in a given calendar year with the same qualifying information. This second qualification excluded less than 0.5 percent of the person numbers and aimed to eliminate person numbers used for multiple people.
While the term "verified person number" is used to describe the HCUP data element visitLink, the values are not recognizable as specific patient information. VisitLink does not include the values of the encrypted person number, date of birth, or gender.
Beginning with the 2009 HCUP data, the revisit variables (VisitLink and DaysToEvent) are included in the Core file of the SID, SASD, and SEDD files, when possible. For 2003-2008 data, the revisit variables are in separate HCUP Supplemental Files for Revisit Analyses.
More information on the revisit variables VisitLink and DaysToEvent is available under the HCUP Supplemental Variables for Revisit Analyses.
|State Specific Notes
Alaska randomly assigns a re-identification number to reported person numbers. The number is not based on any systematically applied set of rules. The patient retains his/her re-identification number permanently, which allows for longitudinal analysis.
In Arkansas, the re-identified person number (PNUM_R) is based on encrypted social security numbers.
California reports encrypted social security numbers as person numbers.
Florida bases their person number on the patient's social security number. The supplied identifiers are encrypted during HCUP processing (PNUM_R). Because of changes in source-provided information, longitudinal analyses using PNUM_R across years are not always possible.
Beginning in 2005, Florida used a different masking method from the one in 2004. From 1998-2004 the coding of the person number is consistent across years. In 1997, source documentation indicated that the Florida encryption routine used to create PNUM from social security numbers was different than previous years. Source-supplied values in the 1996 inpatient data were the same length as prior years, but looked very different.
Staring in 2020, Georgia changed to use Cross Reference Code for HCUP PNUM. Therefore, this Identifiers prior to 2020, and 2020 and after are not consistent. Longitudinal analyses that cross 2020 are not recommended.
Beginning in 2010, Iowa provides a patient identification number. Social security number (SSN), birth date, and gender are used to create a patient identifier. A patient identifier is not assigned if any of the three fields are missing or invalid (e.g., the SSN is not nine digits or is filled with a recurring character).
Beginning in 2013, Iowa provides a new unique ID that is develop using probabilistic matching based on name, gender and date of birth.
Beginning 2017, Iowa changed their coding scheme for person numbers. Therefore, they cannot be used to track patients in prior years.
In 2013, Maryland began providing a new statewide encrypted unique patient identification number (CRISP_EID) to link patients across all hospitals.
Massachusetts supplied encrypted social security numbers. The supplied identifiers are encrypted again during HCUP processing (PNUM_R).
Because of the timing of HCUP data processing for the 1999 NIS, the Massachusetts source file provided to HCUP was an interim file that included records that had failed edit checks. The percent of failed records is very small, ranging from 0.0% to 1.5% (with a mean of 0.4%) for most hospitals. A handful of hospitals had a large percent of failed records. Failed records have one or more of the following errors:
* These errors would have been handled during HCUP data processing.
The Missouri person number (PNUM_R) cannot be used to track patients consistently over time because the coding scheme changed in 2002. Beginning in 2002, Missouri randomly assigns a re-identification number to reported person numbers. The number is not based on any systematically applied set of rules. Nonetheless, the patient retains his/her re-identification number permanently, which allows for longitudinal analysis from 2002 forward.
Beginning with the 2020 data, Nebraska used probabilistic matching based on patient name, gender, and date of birth to generate the patient linkage number. Therefore, the patient linkage numbers prior to 2020 and 2020 and after are not consistent. Longitudinal analyses that cross data year 2020 are not recommended.
From 2002 through 2019, Nebraska provides a patient re-identification number. The Nebraska person number (PNUM/PNUM_S) cannot be used to track patients consistently over time because the coding scheme changed in 2002. Prior to 2002, Nebraska created their unique patient identifier through a 256 byte one-way hashing of the patient's first name, patient's last name, date of birth, and social security number. Beginning in 2002, Nebraska randomly assigns a re-identification number to the individual. The number is not based on any systematically applied set of rules. Nonetheless, the patient retains his/her re-identification number permanently, which allows for longitudinal analysis from 2002 forward.
The New York person number (PNUM/PNUM_R) cannot be used to track patients consistently over time because the coding scheme changed. Beginning in 2005, New York started using a new encryption key which is 22 characters in length. In 2004, New York used a hexadecimal format to mask person numbers. Prior to 2004, a 10-digit encrypted person number (PNUM) was created by New York using the first 2 characters of the last name, the last 2 characters of the last name, the first 2 character of the first name, and the last 4 digits of the person's SSN.
Beginning with the 2008 data, the HCUP data element PNUM_R is missing (.) for AIDS/HIV patients. New York identifies AIDS/HIV records by ICD-9-CM diagnosis code, DRG, or MS-DRG:
Please note that the admitting diagnosis is not retained in the HCUP databases prior to 2012.
North Carolina provides an encrypted social security number. Reporting of the patient's social security number is optional for hospitals in North Carolina. Beginning in the 2000 data, this data element is frequently missing. During HCUP processing, this identifier is re-encrypted.
Utah supplied source-encrypted social security numbers as person numbers. These identifiers are encrypted again during HCUP processing (PNUM_R). Three-digit codes may indicate:
After 7/1/90, it is possible that more than one person could have the same PNUM_R value. Wisconsin derives the identifier from the patient first and last names, making it possible for people with similar names to have the same identifier. This data element, however, can be used in combination with other data elements to track transfers and readmissions. Prior to 7/1/1990 PNUM_R was not available.
|Internet Citation: HCUP Central Distributor SEDD Description of Data Elements - All States. Healthcare Cost and Utilization Project (HCUP). September 2008. Agency for Healthcare Research and Quality, Rockville, MD. www.hcup-us.ahrq.gov/db/vars/sedddistnote.jsp?var=visitlink.
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|Last modified 9/11/08