Definitions of Stage, Grade and Index
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Stage:
The assessment of the extent of pathological lesions in the course of a disease that is likely to be progressive (e.g. stages of periodontal disease, staging of oral tumors).
Grade:
The quantitative assessment of the degree of severity of a disease or abnormal condition at the time of diagnosis, irrespective of whether the disease is progressive (e.g. a grade 2 mast cell tumor based on mitotic figures)
Index:
A quantitative expression of predefined diagnostic criteria whereby the presence and/or severity of pathological conditions are recorded by assessing a numerical value (e.g. gingival index, plaque index).