Definition And Classification of Indices
Russell defines index as:
“A numerical value describing the relative status of a population on a graduated scale with definite upper and lower limits, which is designed to permit and facilitate comparison with other populations classified by the same criteria and methods”
CLASSIFICATION OF INDEX:
1. Based on the direction in which their scores can fluctuate:
- Irreversible index: Measures conditions that will not change scores once established cannot decreases in value on subsequent examination, e.g. Dental caries indices, Fluorosis index.
- Reversible index: Measures conditions that can be changed and scores can increases or decreased in subsequent examinations, e.g. periodontal indices.
2. Depending on extent to which areas of oral cavity are measures:
- Full mouth indices: measure the patient’s entire periodontium or dentition, e.g. Russell’s periodontal index.
- Simplified indices: Measure only a representative sample of the dental apparatus, e.g. OHI-S
3. According to the entity which they can measure:
- Disease index
- Symptom Index
- Treatment Index
In general there are 2 types of index:
- Measures the number or proportions of people in a population with or without a specific condition at a specific point in time or interval of time.
2. Measures the number of people affected and the severity of the specific condition at a specific time or interval of time.
Classified under special categories as:
- Simple index: Measures presence or absence of a condition, eg. An index that measures the presence of dental plaque without an evaluation of its effect on gingiva
- Cumulative index: Measures all the evidence of a condition , past and present , e.g. DMF index for dental caries.