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# Common Measures of Central Tendancy

## Biostatistics

## Community Dentistry

[Soben Peter 4th ed 381-82/ 5th ed 603-04]

Arithmetic mean, Median, Mode are common measures of central tendency.

**a) Arithmetic Mean (x̄)**

- It is simplest measure of central tendency.
- It is obtained by summing up all the observations divided by the number of observations.
- It is not an appropriate measure for very skewed distributions as it is very sensitive to extreme scores.

**b) Median (Md)**

- It is the simplest division of a set of measurements into two halves - the upper and lower half, The point on the scale that divides the group in this way is median.
- Median is insensitive to small numbers of extreme scores in a distribution; therefore it is a very useful measure of central tendency for the highly skewed distributions,
- When the distribution has odd number of elements, middle value is median, When the distribution has even number of elements, the average of two middle scores is Median.

**c) Mode**

- It is the most frequently occurring value in a set of observations,
- If only two scores occur with greatest frequency, the distribution is bimodal.
- If more than two scores occur with greatest frequency, the distribution is multimodal.

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