The HCUP Michigan ambulatory surgery files were constructed from the Michigan Outpatient Data Base (MODB) provided by the Michigan Health & Hospital Association (MHA). The MODB contains outpatient records with a principal ICD-9-CM procedure code between 00.01 and 86.99, inclusive, irrespective of where in the outpatient setting the procedure was performed (ambulatory surgery suite, emergency department, etc).

MHA supplied outpatient data from general acute care and specialty hospitals (e.g., rehabilitation hospitals, osteopathic hospitals) that are a member of the Michigan Health & Hospital Association, with two exceptions. Prior to 2005, information from the Henry Ford System hospitals in Detroit and Munson are not included. These two hospitals account for approximately 4 percent of the outpatient visits in Michigan.