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-comorbidities_icd10
+comorbidities.icd10
 ===================
 
-Comorbidities calculator for R using ICD-9 and ICD-10 based scores
+Comorbidities calculator for R using ICD-9 and ICD-10 based scores. Currently only icd-9 codes are implemented and tested.
+
+Methods to categorize ICD-9-CM codes into sensible disease categories have
+been developed and published by numerous authors.  Two of the most widely
+used such methods are the Deyo adaptation of Charlson index and the
+Elixhauser index.  This package has functions to categorize comorbidites
+into the Deyo-Charlson index, the original Elixhauser index of 30
+comorbidities, and the AHRQ comorbidity index (an update to the original
+Elixhauser method).
+
+This package consists of 3 functions: deyo, elixhauser, and ahrq.
+The functions are very similar in that they each take as input a data frame
+structured such that each row contains a list of ICD-9-CM codes (e.g.
+discharge or admission diagnoses) attributed to a single patient. The
+function goes from row to row comparing the ICD-9-CM codes a patient has
+with the particular comorbidity index that function represents.  If a
+patient has a diagnosis (as indicated by ICD-9-CM code) that is one of the
+diagnoses in the paritcular index chosen, then the patient is considered to
+have this diagnosis.  Regardless of how many different ICD-9-CM codes a
+patient has corresponding to a particular comorbidity category, a
+comorbidity is only counted once.
+
+The value returned consists of a vector and one or two data frames. The
+vector is the total comorbidity count, or in the case of the deyo()
+function, the total Charlson score.  The functions elixhauser() and ahrq()
+return one data frame.  Each row in the data frame is devoted to a
+particular patient, and each column is a diagnosis.  The data frame codes a
+0 if the patient does not have that diagnosis and 1 if the patient does have
+that diagnosis. The deyo() function returns a second data frame, which codes
+the point value of that particular diagnosis in the Charlson score rather
+than a 1.
+
+This package is a work upon Paul Gerrards original comorbidities package.
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