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about emergency department visit data

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  • For each data source, information about data collection and analytical methods, limitations, the citation and additional resources can be found on the Data Sources and Methods page.


Original Source: Canadian Institute for Health Information (CIHI)
Cite as: National Ambulatory Care Reporting System Data, 2003-2017, Canadian Institute for Health Information (CIHI). IntelliHEALTH Ontario, Ministry of Health and Long-Term Care.


Data Collection Methods

  • Hospital emergency departments report patient visit information into the National Ambulatory Care Reporting System (NACRS), which began in July 2000. Data are not considered to be reliable until the fiscal year 2002/2003.
  • The first areas or visit functional centres (VFCs) to report to NACRS were the hospital Emergency Rooms in fiscal year 2002/2003. In fiscal year 2003/2004 other major ambulatory VFCs within the hospital such as Day Surgery, Medical Day/Night Care and specified high-cost clinics such as renal dialysis and cancer clinics were also included.
  • The main diagnostic code used for emergency department visits is based on the patient’s main problem or diagnosis as determined by the emergency department.
  • The main problem variable is coded using International Statistical Classification of Diseases and Related Health Problems, Canada, Version 10, 2007 (ICD-10-CA) codes starting with A through U.
  • A second set of codes for external causes (those starting with V, W, X or Y) are used in the case of an injury to classify the environmental events, circumstances and conditions that caused the injury (e.g., a motor vehicle traffic injury). External cause codes are the principal means of classifying injury deaths but are not used as a main problem for emergency department visits, so they need to be examined separately.
  • The ICD-10-CA codes used for analyses on the Health Status Data website can be accessed here.

Data Analysis Methods

  • The counts presented on the Health Status Data website represent the number of distinct visits and not the number of distinct individuals, as an individual may have multiple visits during the time period examined.
  • ICD-10-CA Chapter 15: Pregnancy, Childbirth and the Puerperium and Chapter 21: Factors influencing health status and contacts with health services were excluded from analysis.
  • Beginning in 2003/2004 an indicator was added that identifies the problem code that was considered to be the ‘Reason for the Visit’ or the reason or symptom that caused the patient to visit the hospital in the first place (e.g., if a patient complains of chest pain on arrival at the emergency department and is found to be suffering from a myocardial infarction/heart attack (MI), the MI would be coded as the ‘main problem’ and the chest pain as one of the other problems and the Reason for the Visit).
  • The main problem codes are grouped into categories based on ICD-10-CA coding. A mutually exclusive sub-set of these groupings are defined as “leading causes of emergency department visits”, which represent specific diseases or conditions of public health interest. ICD groupings which include all residual codes within a chapter not elsewhere classified are not presented on the Health Status Data website as leading causes of emergency department visits. Therefore, the leading causes of emergency department visits include only a selected list of specific diseases or conditions. The ICD-10-CA codes used for these analyses can be accessed here.
  • Within the leading cause of emergency department visits, main problems related to injuries were coded based on Chapter 19 (S & T codes). In contrast, the leading causes of injuries are defined based on the external cause codes. Since multiple external cause codes can be assigned for each emergency department visit record, the count within the leading causes of injuries will be higher than the count of injuries within the leading causes of emergency department visits.
  • Emergency department visit rates are calculated using crude and age-standardization methods. Age-standardized rates are calculated using the direct method of standardization with the 2011 Canadian population as the standard population.


  • Data are not considered to be reliable until 2002/2003.
  • Ambulatory visit data provide only a crude measure of the condition being quantified since a person may not seek care at an emergency department, may visit several times for the same disease or injury event, or may visit more than one hospital for the same disease or injury event.
  • Data are influenced by factors that are unrelated to health status such as availability and accessibility of care, and administrative policies and procedures. This may influence comparisons between areas and over time.
  • Ontario residents visiting hospitals outside of the province are excluded. Areas bordering other provinces may be more affected.


  1. Association of Public Health Epidemiologists in Ontario – National Ambulatory Care Reporting System (NACRS)

Last updated: June 21, 2019

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