Definitions:   Means, Medians and Standard Deviations

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Mean: The average of all the values of a variable such as age, weight-for-age z-score, income, or hemoglobin level.


Median: The middle value in a distribution of values in a variable-- the value at which 50% of cases are above and 50% are below. 
If the median differs much from the mean value, then investigate the overall distribution of values.


Standard Deviations: The standard deviation indicates the variation in the group of measurements. When the values of a set of observation lie close to the mean, the dispersion is less than when they are scattered over a wide range.  A difference in the standard
deviation of a variable when comparing different groups will indicate possible data errors.