Dear Editor,
We read with great interest the article published by Chhabra et al.[1] titled, “Association of near work and dim light with myopia among 1400 school children in a district in North India” published in the Indian Journal of Ophthalmology. The authors have done a commendable job in highlighting visual acuity among school children, which is envisaged in the National Programme for Control of Blindness and Visual Impairment (NPCBVI) too. However, there are a few concerns regarding this study.
It has been mentioned by the authors in the methods section that this was a prospective interventional study that was done randomly among schools of a north Indian district. However, the present study appears to be a cross-sectional study design, with prescribing of spectacles as per the ethical principles of the Declaration of Helsinki. An interventional study design is defined as one in which the researcher intervenes at some point throughout the study. The types include pre-post study design, randomized and non-randomized control trials, and quasi-experiments.[2] In the current study, there was no measurement of outcome after the intervention was done, and hence it cannot be termed as pre-post study design.
The title of the present study refers to the association of near work and dim light with myopia. However, in the result section, the term “correlation” has been mentioned repeatedly for the same. In a stricter sense, association is defined as a concurrence of two variables more often than would be expected by chance. On the other hand, correlation indicates the degree of association between two characteristics with values of correlation coefficients ranging from −1 to +1.[3] For association, Chi-squared test is commonly used whereas for measuring correlation, the Pearson and Spearman correlation tests are applied. The mentioning of the term “correlation” in the results and discussion sections appears to be misleading where the term “association” should have been used.
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Conflicts of interest
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References
- 1.Chhabra S, Rathi M, Sachdeva S, Rustagi IM, Soni D, Dhania S. Association of near work and dim light with myopia among 1400 school children in a district in North India. Indian J Ophthalmol. 2022;70:3369–72. doi: 10.4103/ijo.IJO_634_22. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Thiese MS. Observational and interventional study design types;an overview Biochem Med (Zagreb) 2014;24:199–210. doi: 10.11613/BM.2014.022. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Park K. Park's Textbook of Preventive and Social Medicine. 24th ed. Banaridas Bhanot Publishers;2017. :92. [Google Scholar]