<P> The most common measures of central tendency are the arithmetic mean, the median and the mode . A central tendency can be calculated for either a finite set of values or for a theoretical distribution, such as the normal distribution . Occasionally authors use central tendency to denote "the tendency of quantitative data to cluster around some central value ." </P> <P> The central tendency of a distribution is typically contrasted with its dispersion or variability; dispersion and central tendency are the often characterized properties of distributions . Analysts may judge whether data has a strong or a weak central tendency based on its dispersion . </P> <P> The following may be applied to one - dimensional data . Depending on the circumstances, it may be appropriate to transform the data before calculating a central tendency . Examples are squaring the values or taking logarithms . Whether a transformation is appropriate and what it should be, depend heavily on the data being analyzed . </P> <Dl> <Dt> Arithmetic mean or simply, mean </Dt> <Dd> the sum of all measurements divided by the number of observations in the data set . </Dd> <Dt> Median </Dt> <Dd> the middle value that separates the higher half from the lower half of the data set . The median and the mode are the only measures of central tendency that can be used for ordinal data, in which values are ranked relative to each other but are not measured absolutely . </Dd> <Dt> Mode </Dt> <Dd> the most frequent value in the data set . This is the only central tendency measure that can be used with nominal data, which have purely qualitative category assignments . </Dd> <Dt> Geometric mean </Dt> <Dd> the nth root of the product of the data values, where there are n of these . This measure is valid only for data that are measured absolutely on a strictly positive scale . </Dd> <Dt> Harmonic mean </Dt> <Dd> the reciprocal of the arithmetic mean of the reciprocals of the data values . This measure too is valid only for data that are measured absolutely on a strictly positive scale . </Dd> <Dt> Weighted arithmetic mean </Dt> <Dd> an arithmetic mean that incorporates weighting to certain data elements . </Dd> <Dt> Truncated mean or trimmed mean </Dt> <Dd> the arithmetic mean of data values after a certain number or proportion of the highest and lowest data values have been discarded . <Dl> <Dt> Interquartile mean </Dt> <Dd> a truncated mean based on data within the interquartile range . </Dd> </Dl> </Dd> </Dl>

Measure of central tendency vs measures of dispersion