A central concept in any epidemiological investigation is that of appropriate data description. A number of methods are available for describing data, and the selection of the incorrect one can result in a loss of information, or more seriously, a misleading estimate. The most appropriate measure to use will depend on the [[Data types|type of data]] in question.<br>
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==Qualitative data==
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Qualitative data may or may not have an intrinsic order, and can always be described using proportions (i.e. the proportion of animals in each 'category'). The '''mode''' can also be a useful measure of central tendency, in the case of ordinal data. There are no meaningful measures of spread in these cases, as the difference between adjacent categories is not standard.
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==Quantitative data==
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These data can be described according to a '''measure of central tendency''', '''spread''' and the '''shape''' of their distribution.