Journal of Family Medicine and Primary Care

: 2018  |  Volume : 7  |  Issue : 3  |  Page : 647--648

Cautious use of absolute and relative precision while calculating sample size

Preeti Usha, Ajeet Singh Bhadoria, Surekha Kishore 
 Department of Community and Family Medicine, All India Institute of Medical Sciences, Rishikesh, Uttarakhand, India

Correspondence Address:
Dr. Ajeet Singh Bhadoria
Department of Community and Family Medicine, All India Institute of Medical Sciences, Rishikesh, Uttarakhand

How to cite this article:
Usha P, Bhadoria AS, Kishore S. Cautious use of absolute and relative precision while calculating sample size.J Family Med Prim Care 2018;7:647-648

How to cite this URL:
Usha P, Bhadoria AS, Kishore S. Cautious use of absolute and relative precision while calculating sample size. J Family Med Prim Care [serial online] 2018 [cited 2021 Jun 24 ];7:647-648
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Dear Editor,

Recently published article entitled “Locomotor problems among rural elderly population in a District of Aligarh, North India” has referred an extremely topical subject of locomotor problems among the most vulnerable geriatric population residing in a rural area.[1] Authors have rightly targeted sociodemographic risk factors to document their relationship with the presence of locomotor problems among the elderly population.

However, we have following concerns about this study and intend to highlight here to help readers to be cautious before drawing conclusions.

Related to prevalence, the sample size calculated has some major concerns. It was calculated considering lowest prevalence and absolute precision. With any absolute precision, maximum sample size is attained with 50% prevalence.[2] The concept of lower the prevalence and higher the sample size is correct if relative precision is taken to calculate the sample size. Thus, the sample size of 225 was inadequate and study was underpowered to document the desired prevalenceAuthors have mentioned that a pilot study was done to get baseline information about the health problems. The findings of the pilot study should have been utilized to calculate the sample size using appropriate statisticsThe utilization of systematic random sampling to select 225 elderlies from total sampling frame of 1018 is well justifiable. However, how and why the probability proportionate to size (PPS) method was used is not clarified. PPS is used to select clusters in cluster sampling method.[3] If it is used, then authors should have shared the details of the clusters and should have considered the design effect in calculating the sample size to take care of intraclass correlation among the clustersImportant sociodemographic components such as socioeconomic status including income and type of family in which elderlies were living and family size were not included in the study. Enough evidences are available to acknowledge their role with respect to locomotor and other disabilities among geriatric population [4]Multivariate regression analysis could have been utilized to document the adjusted odds ratio for working status after adjusting for the nonmodifiable significant risk factors such as age and genderAuthors have excluded severely ill or moribund individuals which will lead to underestimation of prevalence of locomotor disability as the definition utilized itself includes those with loss or lack of normal ability to execute distinctive activities associated with day-to-day routine.[5] These people might also have locomotor and other problems related to old age.

Thus, the prevalence might be underestimated, study looks underpowered with inadequate sample size, and sociodemographic risk factor profile was incomplete. Therefore, readers need to be careful to reach to any conclusion.

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1Maroof M, Ahmad A, Khalique N, Ansari MA. Locomotor problems among rural elderly population in a district of Aligarh, North India. J Fam Med Prim Care 2017;6:522-5.
2Lwanga SK, Lemeshow S. Sample Size Determination in Health Studies: A Practical Manual. Geneva: WHO; 1991.
3Bennett S, Woods T, Liyanage WM, Smith DL. A simplified general method for cluster-sample surveys of health in developing countries. World Health Stat Q 1991;44:98-106.
4Agrawal A. Disability among the elder population of India: A public health concern. J Med Soc 2016;30:15-9.
5Disabled Persons in India Report. National Sample Survey Organization (NSSO) 58th Round (July-December 2002), Ministry of Statistics and Programme Implementation Government of India; December 2003 Report No: 485. Available from: [Last accessed on 2018 Feb 09].