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| Year : 2014 | Volume
: 62
| Issue : 5 | Page : 584 |
Why standard deviation as a measure of dispersion needs a mention in a dataset?
Anjali Mahajan
Department of Community Medicine, Indira Gandhi Medical College, Shimla, Himachal Pradesh, India
| Date of Web Publication | 12-Nov-2014 |
Correspondence Address:
Anjali Mahajan
Department of Community Medicine, Indira Gandhi Medical College, Shimla, Himachal Pradesh
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/0028-3886.144523
How to cite this article:
Mahajan A. Why standard deviation as a measure of dispersion needs a mention in a dataset?. Neurol India 2014;62:584 |
Sir,
We have read with interest the article by Gupta et al., [1] however, we have some concerns. Why standard deviation as a measure of dispersion needs a mention in a dataset? The authors have conducted a retrospective analysis of records of all patients with ruptured vertebral artery posterior inferior cerebellar artery (VA-PICA) junction aneurysms over five years and concluded that endovascular therapy of ruptured proximal PICA aneurysms is possible and safe with the use of adjuvant devices and should be considered as first line treatment. Thirteen patients who underwent endovascular treatment for ruptured saccular VA-PICA junction aneurysms were the focus of this research. My submission in this regard is that the authors have mentioned the age of 13 study subjects along with the overall mean and range of age in years. The range, inter-quartile range and standard deviation are the measures that indicate the amount of variability within a dataset. [2] The range is the simplest measure of variability to calculate but can be misleading if the dataset contains extreme values as it is based solely on the two most extreme values within any dataset. [3] If one of these values is either exceptionally high or low (sometimes referred to as outlier), it will result in a range that is not typical of the variability within the dataset. Moreover, the dataset that has the greater range will also have the greater SD, but not always. On the other hand, the standard deviation is a measure that summarizes the amount by which every value within a dataset varies from the mean. [4] Effectively it indicates how tightly the values in the dataset are bunched around the mean value. It is the most robust and widely used measure of dispersion. Unlike the range, standard deviation takes into account every variable in the dataset. My viewpoint is that if age of males and females had been mentioned separately along with their means and standard deviations, it would have been more informative. Since the range of age of study subjects mentioned in the article by the authors is very wide i.e. 14 to 60 years with gender differences of age not mentioned, this information keeps one oblivious of the effect of age differences in both the genders on the prognosis of endovascular treatment for ruptured saccular VA-PICA junction aneurysms.
| » References | |  |
| 1. | Gupta V, Mulimani N, Kumar A, Ahuja C, Mathuria SN, Khandelwal N. Endovascular treatment of ruptured proximal PICA aneurysms: A single-center 5-years experience. Neurol India 2014;62:269-75.  [ PUBMED]  |
| 2. | Armitage P, Berry G, Matthews JN. Statistical Methods in Medical Research. 4 th ed. UK: Blackwell Publishing;2002. |
| 3. | Whitley E, Ball J. Statistics review 1: Presenting and summarising data. Crit Care 2002;6:66-71. |
| 4. | Kirkwood BR. Essentials of medical Statistics. London: Blackwell Science Ltd;.1988. |
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