Academic journal article Indian Journal of Psychiatry

Age as a Variable: Continuous or Categorical?

Academic journal article Indian Journal of Psychiatry

Age as a Variable: Continuous or Categorical?

Article excerpt

Byline: Chittaranjan. Andrade

Sir,

In a strongly worded letter, Mondal [1] affirms that age is indeed a number that can be categorized in groups. I agree. In fact, I had stated at least 3 specific circumstances in which this may be desirable: For administrative purposes; when the data cannot be accurately recorded; and when the data are skewed.[2]

A classical example for the categorization of continuous data is for public health purposes, as when patients are classified into pediatric, adult, and geriatric groups for health-care resource allocation; and in an allied context, for everyday descriptive purposes, as when people are referred to as being in their early twenties or mid-forties. The classroom cartoon in the letter [1] reflects this latter situation. However, there is a world of difference between a classroom in which research is talked about in conversational terms and a research article in which precision is expected because inferential statistical tests will be applied to the data.

Mondal [1] suggests that age can be viewed as a discrete variable because it is commonly expressed as an integer in units of years with no decimal to indicate days and presumably, hours, minutes, and seconds. If so, would ratings of psychopathology on various clinical scales or ratings of cognitive performance on various neuropsychological tests be considered discrete outcomes because no decimal ratings are assigned? Certainly not. The difference between ordinal data and data that are measured using an interval or ratio scale does not depend on the actual values recorded; it depends on the potential of the scale to accommodate decimal values. …

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