Indian Journal of PsychiatryIndian Journal of Psychiatry
Home | About us | Current Issue | Archives | Ahead of Print | Submission | Instructions | Subscribe | Advertise | Contact | Login 
    Users online: 1339 Small font sizeDefault font sizeIncrease font size Print this article Email this article Bookmark this page


    Advanced search

    Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
    Email Alert *
    Add to My List *
* Registration required (free)  


 Article Access Statistics
    PDF Downloaded125    
    Comments [Add]    

Recommend this journal


 Table of Contents    
Year : 2017  |  Volume : 59  |  Issue : 4  |  Page : 524-525
Age as a variable: Continuous or categorical?

Department of Psychopharmacology, National Institute of Mental Health and Neurosciences, Bengaluru, Karnataka, India

Click here for correspondence address and email

Date of Web Publication18-Jan-2018

How to cite this article:
Andrade C. Age as a variable: Continuous or categorical?. Indian J Psychiatry 2017;59:524-5

How to cite this URL:
Andrade C. Age as a variable: Continuous or categorical?. Indian J Psychiatry [serial online] 2017 [cited 2021 Jan 16];59:524-5. Available from:


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. Whereas there may not be a benefit in excessive precision in recording age in adults, age in children is often expressed in months rather than years, so that the desired precision can be obtained, and age in neonates is expressed in days for the same reason.

The suggestion that education be categorized is suitable for administrative or everyday descriptive contexts. It is incorrect when education is treated as an independent variable the effect of which on outcomes is intended to be studied using inferential statistical procedures. The reasons were stated in my earlier article.[2] Operationalizing education in years is particularly useful when subjects complete extra courses, training, or diplomas at a horizontal level without gaining an additional degree.

There is no challenge at all in presenting continuous and categorical data in the same table, along with the appropriate inferential statistical results. In fact, this is commonly done. Any journal of good standing will contain plenty of examples.

Concluding with a note of humor, as Mondal [1] displays in his letter: Would he state his age as, say, “21-30” years in a job application or would he state a precise number?

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

   References Top

Mondal H. Age is a number which can be categorized in groups. Indian J Psychiatry 2017;59:InPress.  Back to cited text no. 1
[PUBMED]  [Full text]  
Andrade C. Age is a number, not a group. Indian J Psychiatry 2017;59:248.  Back to cited text no. 2
[PUBMED]  [Full text]  

Correspondence Address:
Chittaranjan Andrade
Department of Psychopharmacology, National Institute of Mental Health and Neurosciences, Bengaluru, Karnataka
Login to access the Email id

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/psychiatry.IndianJPsychiatry_354_17

Rights and Permissions