(arithmetic mean) The average of a series of quantities, obtained by adding up all the observed values and dividing by the total number of observations. If a normal curve were plotted from an infinitely large number of observations, then the mean (and the *

median and *

mode ) would be the distance from the origin of the axes to the centre point of the curve, represented by the symbol μ. However when sample size is limited, as always occurs in practice, then the estimated mean, rather than the median or mode, gives the best estimate of the true mean.