Changes

'''Systematic error''', or 'bias' is of particular importance in any epidemiological investigation. There are a number of types of bias, which may be classified broadly as either selection bias or information bias:

'''Systematic error''', or 'bias' is of particular importance in any epidemiological investigation, and should be avoided wherever possible. Biases will reduce the '''validity''' or '''accuracy''' of any results obtained. There are a number of types of bias, which may be classified broadly as either selection bias or information bias, and which will differ in the case of different [[study designs]]

==Selection bias==

==Selection bias==