POSTGRADUATE CORNER

Year : 2011  |  Volume : 2  |  Issue : 3  |  Page : 214-215

Measures of central tendency: Median and mode

S Manikandan
Assistant Editor, JPP, India

Correspondence Address:
S Manikandan
Indira Gandhi Medical College and Research Institute Hospital, Pondicherry
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/0976-500X.83300

Introduction

Median

1. It is easy to compute and comprehend.
2. It is not distorted by outliers/skewed data. ^[4]
3. It can be determined for ratio, interval, and ordinal scale.

1. It does not take into account the precise value of each observation and hence does not use all information available in the data.
2. Unlike mean, median is not amenable to further mathematical calculation and hence is not used in many statistical tests.
3. If we pool the observations of two groups, median of the pooled group cannot be expressed in terms of the individual medians of the pooled groups.

Mode

1. It is the only measure of central tendency that can be used for data measured in a nominal scale. ^[5]
2. It can be calculated easily.

1. It is not used in statistical analysis as it is not algebraically defined and the fluctuation in the frequency of observation is more when the sample size is small.

Position of Measures of Central Tendency

Figure 1: The relative position of the various measures of central tendency. (a) Normal distribution (b) Positively (right) skewed distribution (c) Negatively (left) skewed distribution Click here to view

Selecting the Appropriate Measure

1. There are few extreme scores in the distribution.
2. Some scores have undetermined values.
3. There is an open ended distribution.
4. Data are measured in an ordinal scale.
5. Mode is the preferred measure when data are measured in a nominal scale. Geometric mean is the preferred measure of central tendency when data are measured in a logarithmic scale. ^[8]

References

1.	Swinscow TD, Campbell MJ. Statistics at square one. 10 th ed(Indian). New Delhi: Viva Books Private Limited; 2003.
2.	Gravetter FJ, Wallnau LB. Statistics for the behavioral sciences. 5 th ed. Belmont: Wadsworth - Thomson Learning; 2000.
3.	Sundaram KR, Dwivedi SN, Sreenivas V. Medical statistics principles and methods. 1 st ed. New Delhi: B.I Publications Pvt Ltd; 2010.
4.	Petrie A, Sabin C. Medical statistics at a glance. 3 rd ed. Oxford:Wiley-Blackwell;2009.
5.	Norman GR, Streiner DL. Biostatistics the bare essentials. 2 nd ed. Hamilton: B.C. Decker Inc; 2000.
6.	SundarRao PS, Richard J. Introduction to biostatistics and research methods. 4 th ed. New Delhi: Prentice Hall of India Pvt Ltd; 2006.
7.	Glaser AN. High Yield Biostatistics. 1 st Indian Ed. New Delhi:Lippincott Williams and Wilkins;2000.
8.	Dawson B, Trapp RG. Basic and Clinical Biostatistics. 4 th ed. New York: Mc-Graw Hill; 2004.

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