Max Rady College of Medicine
Concept: Undercounting Hospital Visits
Last Updated: 2004-06-04
Ambulatory visits definition has been simplified and can be generated using a SAS macro on MCHP systems. Most of this concept is retained for historical purposes. See the
Ambulatory Visits - Physicians
concept for more recent information.
Service Date falls between or on Admission and Separation date irrespective of what hospital is coded.
If there is an OPD/ER flag set to 'O','E' and the physician service is on the date of admission or separation it is counted as an ambulatory visit not in-hospital.
- See SAS code below (internal access only) for linking with hospital data and defining ambulatory visits.
In-patient visits are defined as a contact with a physician that occurs during a time period where a patient has been admitted to a hospital.
- Hence a true in-patient contact should have a corresponding hospital discharge abstract.
We linked the in-patient visit definition from the medical services/physician claims data against the hospital discharge abstracts data. Those occurring during a hospital stay are true in-patients.
Those without a corresponding hospital discharge abstract are visits that we have neglected in all our analysis.
- Throughout the years we have under-estimated the number of visits.
Based on a March 27, 2002 researchers meeting, the following definition for hospital visit was accepted.
The current ambulatory visits (ambvis='1') misses hospital visits for outpatient cases. These visits are misclassified as in-patient visits.
In 1992, it was noted that "we may miss visits that did not occur when the patient was admitted to hospital". It was estimated that "this may represent a 2% under-estimation of ambulatory claims overall".
Hospital visits and magnitude of the under-estimation
Overall visits: The proportion of the missing hospital visits is growing over-time. While it was 2% in 1992 it reached 4 + % in 1998.
Specialist Visits: The bulk of the missing visits correspond to outpatient visits to specialist. In 1998 the under-estimate reached 14%.
Consults visits: For the period 1993-1998 the under-estimate for consults was between 16 to 23%.
- GP visits: less than 1% under-estimate throughout the period.
Special attention should be paid to the effect of the under-estimate when dealing with income quintiles.
The lower the income, the higher the proportion of missing visits:
Income Quintile % Missing
% Missing Specialist
Visits in dollars
% Missing Consult Visits
Q1 (poorer) 16.7 20.5 24.1 Q2 15.3 18.2 20.4 Q3 14.6 17.4 20.4 Q4 13.7 16.1 19.6 Q5 (wealthier) 13.5 15.3 19.7
- Analysis such as utilization rates or diagnosis analysis need to incorporate these hospitals visits.
- Data sets are available for the period 1993-1998 (hospvis93 to hospvis98)- contact Bogdan for more information.
- Health Measures
Manitoba Centre for Health Policy
Community Health Sciences, Max Rady College of Medicine,
Rady Faculty of Health Sciences,
Room 408-727 McDermot Ave.
University of Manitoba
Winnipeg, MB R3E 3P5 Canada