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Descriptive epidemiology aims to describe the distribution of disease in terms of animal, place and time:<br>

Descriptive epidemiology aims to describe the distribution of disease in terms of animal, place and time, as shown below. In a purely descriptive study, no attempt is made to formally investigate reasons for the patterns of disease observed, although hypotheses regarding possible reasons will commonly be generated and developed as a result of these investigations. A description of the different types of descriptive studies is provided [[Study design#Descriptive studies|elsewhere]].<br>

=='''Animal''' ''(which animals are affected)''==

=='''Animal''' ''(which animals are affected)''==

=='''Time''' ''(when cases occur)''==

=='''Time''' ''(when cases occur)''==

Again, the timing of disease is accounted for to some degree in all investigations - meaning that a study investigating the worldwide incidence of Rinderpest in 1900 would give very different results from that in 2010. However, some studies may further investigate and quantify the temporal pattern of disease. One example of this is outbreak investigation,  where the number of cases of disease within a population over time may be plotted in the form of an 'epidemic curve'. This can provide useful information regarding trends of disease, and may advise upon the effectiveness of any control measures instigated.<br>

Again, the timing of disease is accounted for to some degree in all investigations - meaning that a study investigating the worldwide incidence of [[Rinderpest]] in 1900 would give very different results from that in 2010. However, some studies may further investigate and quantify the temporal pattern of disease. One example of this is outbreak investigation,  where the number of cases of disease within a population over time may be plotted in the form of an 'epidemic curve'. This can provide useful information regarding trends of disease, and may advise upon the effectiveness of any control measures instigated.<br>

=='''Descriptive studies'''==

=='''Sampling'''==

Descriptive studies are essential in the investigation of the levels of disease in populations, as well as in the crude monitoring of the effect of an intervention or exposure to a risk factor. In a purely descriptive study, no attempt is made to formally investigate reasons for the patterns of disease observed, although hypotheses regarding possible reasons will commonly be generated and developed as a result of these investigations. It is of vital importance that the ''source population'' of a descriptive study is clearly defined (in terms of animal, place and time), and that forms of ''selection bias'' are minimised, in order to allow accurate inferences to be made based on the results. These concepts are covered in other sections.

A very commonly used type of descriptive studies is the '''survey''', which are very useful in the investigation of the [[Measures of disease frequency|levels of disease in populations]], as well as in the crude monitoring of the effect of an intervention or exposure to a risk factor. In these cases, it is of vital importance that the sample is representative of the ''source population'', which means that this population must be clearly defined in terms of animal, place and time, and that forms of ''selection bias'' must be minimised. These concepts are covered in other sections.

[[Category:Veterinary Epidemiology - Introduction|C]]

[[Category:Veterinary Epidemiology - General Concepts|E]]