Definition of Reported Measures 

  • Hospitalizations due to Asthma represents California residents who were hospitalized due to Asthma; expressed as a rate per 10,000 California residents.
  • Emergency department (ED) visits due to Asthma represents California residents who visited an ED; expressed as a rate per 10,000 California residents

How to Read Tables, Charts, and Maps 

  • The 95% confidence interval (CI) is the range of values that likely contains the true rate in the population.
  • Conventional rates express the number of outcomes relative to the size of the population.  N/A indicates that the data are not available due to the number of events being less than 12.
  • Modeled rates are similar to conventional rates except that they further take into account the frequency of events in surrounding areas.  Modeled rates can be useful when there aren't enough events in an area to calculate rates in the conventional manner, and they are often useful for examining regional trends.
  • Total counts are listed next to conventional rates unless the total number of events is less than 12. They are typically not listed next to modeled rates.
  • Some counties have a greater proportion of people who are old or young than other counties, which makes it difficult to compare across counties or over time. Scientists often fix this problem through a technique called age adjustment so comparisons can be made. In addition to crude rates, we also present age-adjusted rates.
  • Effective October 1, 2015, hospital record (OSHPD) data transitioned from ICD-9 to ICD-10-CM. Differences between counts and rates in years prior to 2015 compared with 2015 and subsequent years could be a result of this coding change and not an actual difference in the number of events. 

Data Sources

  • Emergency Department and Patient Discharge Datasets from the State of California, Office of Statewide Health Planning and Development (OSHPD).
  • Denominators for county level rates are based on estimates from the California Department of Finance.
  • Denominators for zip-code level rates are based on population estimates from a private vendor. 


  • Cases of Asthma hospitalizations and emergency department visits are identified by using the following ICD-9-CM: 493; or ICD-10-CM code: J45 as the primary diagnosis.

Limitations of the Data

  • Data Collection Purpose- Diagnosis codes are recorded by hospitals for reimbursement purposes and not for public health surveillance.  
  • Low-level of resolution- Hospitals are not mandated to report patient addresses.  The level of geographic resolution of the data is limited to state, county, and zip code.
  • Zip code level data- Zip codes are not geographic areas; Zip codes may change from year to year and even within a year; Zip codes can cross city or county boundaries; and Zip code populations are estimates.

Suggested Citation

Tracking California, Public Health Institute. Asthma Related Emergency Department & Hospitalization data. Accessed [Month/Day/Year] from

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