Classification of hospital patients as "surgical." Implications of the shift to ICD-9-CM

Using a nearly complete set of hospital discharge abstracts for Michigan in 1980, the authors offer evidence that the shifts in diagnostic and procedure coding (from HICDA-2 to ICD-9-CM) and associated class definitions may have affected both estimates of surgical/nonsurgical use rates and expected lengths of stay of operated versus nonoperated patients as defined using Commission on Professional and Hospital Activities length-of-stay texts.