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Geographical skills theory
Frequency diagrams are useful to plot the distribution of values in your data set.
They give a good visual representation of whether the 2 sets are different and
allow frequencies to be compared.
Skew is a term used to describe the distribution of data. Data is skewed if the
distribution isn't symmetrical. If the mode is lower than the mean it is negatively
skewed and if it is higher than the mean then it is positively skewed.
Kurtosis describes the amplitude of the data or its shape. Distributions can be
peaked, flat or in between.