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Table of Contents 
CORRESPONDENCE
Year : 2018  |  Volume : 63  |  Issue : 1  |  Page : 82-83
Authors' reply to critical comment on “Vitamin D level in alopecia areata”


1 Department of Dermatology, STD and Leprosy, Government Medical College, University of Kashmir, Srinagar, Jammu and Kashmir, India
2 Department of Preventive and social Medicine, Government Medical College, University of Kashmir, Srinagar, Jammu and Kashmir, India

Date of Web Publication13-Feb-2018

Correspondence Address:
Yasmeen Jabeen Bhat
Department of Dermatology, STD and Leprosy, Government Medical College, University of Kashmir, Srinagar, Jammu and Kashmir
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijd.IJD_15_18

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How to cite this article:
Bhat YJ, Haq IU, Hassan I, Sajad P, Latif I. Authors' reply to critical comment on “Vitamin D level in alopecia areata”. Indian J Dermatol 2018;63:82-3

How to cite this URL:
Bhat YJ, Haq IU, Hassan I, Sajad P, Latif I. Authors' reply to critical comment on “Vitamin D level in alopecia areata”. Indian J Dermatol [serial online] 2018 [cited 2019 Sep 16];63:82-3. Available from: http://www.e-ijd.org/text.asp?2018/63/1/82/225461




Sir,

We thank the authors for showing keen interest in our article.[1] We would like to clear the doubts that have been raised regarding our article.

The concerns related to the methodology that have been raised are very relevant. The issue of study design is important. It depends on the outcome and the exposure variables in the study. In our study, alopecia areata (AA) is “the outcome of interest” and vitamin D level is “the exposure of interest”. Our research hypothesis was that “lower Vitamin D levels increase the risk of developing AA” and we have sampled on the basis of the outcome. We have studied exposures among AA patients (cases) and other patients (controls). We have designed a case–control study since we have sampled on the basis of the outcome (AA). The cross-sectional study design has been erroneously mentioned due to the notion that the patients were not followed up. We acknowledge that the mistake has been pointed out.

Patients with AA who successively presented to our outpatient department were recruited. The exclusion criteria have been mentioned in the material and methods section.

Sample size is a not an issue in this study. The study was designed to be done during the summer months. We recruited all AA patients during our study period (May to October). We did not calculate sample size for our study apriori. However, the study results reveal that our study had a good precision and a large effect size. The 95% confidence interval for the difference between Vitamin D levels among the AA patients versus the controls was −10.9 ng/ml–−6.9 ng/ml in our study.[2]

The effect size, Cohen's d, in our study was 2.05, which is huge effect size.[3]

Further, a post hoc power analysis using G Power was done.[4]

The power in our study approaches 100% at α value = 0.05, df = 83, and effect size = 2.05.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

1.
Bhat YJ, Latif I, Malik R, Hassan I, Sheikh G, Lone KS, et al. Vitamin D level in alopecia areata. Indian J Dermatol 2017;62:407-10.  Back to cited text no. 1
[PUBMED]  [Full text]  
2.
Kirkwood BR, Sterne JA. Essential Medical Statistics. 2nd ed. Malden, MA: Blackwell Science; 2003. p. 501.  Back to cited text no. 2
    
3.
Sawilowsky SS. New effect size rules of thumb. J Mod Appl Stat Methods 2009;8;597-9.  Back to cited text no. 3
    
4.
Faul F, Erdfelder E, Lang A, Buchner A. G Power 3: A flexible statistical power analysis program for the social, behavioural, and biomedical sciences. Behaviour Research Methods 2007;39:175-91.  Back to cited text no. 4
    




 

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