Epidemiology: Measuring Oral Diseases

In oral epidemiology, there are a number of crucial terms that will help dentists to understand how oral disease data is measured and presented. These include:

Index: This is a standard method of rating a disease in which there is a graduated, numerical scale with values corresponding to specific criteria. Types of measurement scales for indices include:

nominal, which simply names conditions;

ordinal, which lists conditions in order of severity;

interval or ratio, which establishes a mathematical relationship;

irreversible, which measures cumulative conditions that cannot be reversed (such as enamel loss due to erosion);

reversible, which measures conditions that can be reversed (such as gingivitis).2,3

An index is only valuable if the information it reports is:

Valid: An index must be designed to measure the aspect of disease that it is intended to measure and correspond to clinical stages of the disease.2,3

Reliable: An index should be reproducible and repeatable, and should provide consistent measurement at any given time under a variety of conditions.2,3

Clear, Simple, Objective: An index should have clearly stated, unambiguous criteria with mutually exclusive categories, and should be simple enough for an examiner to memorize and score using the criteria.2,3

Quantifiable: An index must present data that can be numerically analyzed and treated. Group status should be expressed by distribution, mean, median, or other statistical measures.2,3

Sensitive: An index should identify small yet significant shifts in the condition studied.2,3

Acceptable: The use of the index should not be unnecessarily painful, time-demanding, or demeaning to subjects.2,3

Video 1. What are the important characteristics of a valid index, with reference to a disease such as dental caries?

The most important characteristic for a valid index which is used to measure disease such as dental caries, is that the index factor has to reflect the actual disease situation. For example, if the index indicates that there is disease it should be reflected in actual disease level, which can be measured by what we call a “gold standard.” So, in this situation usually we refer to the histological findings. If it says enamel caries then it should appear in the histological observations that the caries status is still within the enamel. And, at that, they should know the characteristics that require. One is that they should be reliable, or be reproducible. This means that a different examiner, or the same examiner may repeat observations and are able to arrive at the same recording. And they need to have very clear criteria, so that the people understand what the index code means. So all these are the basic characteristics or requirements of a valid index.