A longitudinal cohort study was conducted in 1500 community-dwelling adults 65 years or older. The association between several biomarkers measured at baseline and 4-year mortality was evaluated accounting for possible confounders, including comorbidity. Comorbidity refers to the co-existence of several other diseases.In this study, the following types of comorbidities were considered: myocardial infarction, heart failure, stroke, hypertension, diabetes and chronic kidney disease.Thus, the variable comorbidity has the the following 6 values:myocardial infarction, heart failure, stroke, hypertension, diabetes and chronic kidney disease.

What kind of variable is comorbidityin this study?