Sir,
Singh et al.[1] studied the association between leisure-time physical activity and the cross-sectional prevalence of depression among the youth of Kangra district in Himachal Pradesh. Although this was a prospective study, they used only a single measure of physical activity and only a single measure of depression, and they examined very few confounding and mediating variables. Given that the association between physical activity and mental health has been known for decades,[2,3] their study breaks no new ground.
Curiously, although they sampled adults, they administered the Center for Epidemiologic Studies Depression Scale for Children. Besides being inappropriate for adults, this instrument has not been validated in the Indian population, and there is no support for the validity of the score used to define caseness in the Kangra sample. This scale has also been criticized for being non-specific, with ill-defined cut-off values.[4]
Further, by excluding persons with diagnosed mental health problems, the authors might have excluded depression, which was the very outcome that they sought to identify using their screening instrument.
Finally, they operationalized leisure-time physical activity and depression scores as categorical variables instead of as continuous variables; categorization of continuous data in statistical analysis has many limitations and should not be performed unless there are specific reasons to do so.[5,6]
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Conflicts of interest
There are no conflicts of interest.
REFERENCES
- 1.Singh M, Sharma P, Raj D, Sharma S, Kaushal A, Raina SK. Leisure time physical activity and risk of developing depression among the youth of Kangra district, Himachal Pradesh, India. Indian J Psychol Med. 2018;40:426–32. doi: 10.4103/IJPSYM.IJPSYM_85_18. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Stubbs B, Vancampfort D, Smith L, Rosenbaum S, Schuch F, Firth J. Physical activity and mental health. Lancet Psychiatry 2018 Sep 20. [Last cited on 2018 Oct 21]. Available from: https://www.thelancet.com/journals/lanpsy/article/PIIS2215-0366(18)30343-2/abstract . [DOI] [PubMed]
- 3.Stephens T. Physical activity and mental health in the United States and Canada: Evidence from four population surveys. Prev Med. 1988;17:35–47. doi: 10.1016/0091-7435(88)90070-9. [DOI] [PubMed] [Google Scholar]
- 4.Olsson G, von Knorring AL. Depression among Swedish adolescents measured by the self-rating scale Center for Epidemiology Studies-Depression Child (CES-DC) Eur Child Adolesc Psychiatry. 1997;6:81–7. doi: 10.1007/BF00566670. [DOI] [PubMed] [Google Scholar]
- 5.Streiner DL. Breaking up is hard to do: The heartbreak of dichotomizing continuous data. Can J Psychiatry. 2002;47:262–6. doi: 10.1177/070674370204700307. [DOI] [PubMed] [Google Scholar]
- 6.Andrade C. Categorizing continuous variables. Can J Psychiatry. 2002;47:35–6. doi: 10.1177/070674370204700916. [DOI] [PubMed] [Google Scholar]