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====Non-differental information bias====

====Non-differental information bias====

Non-differential bias occurs when the chance of bias is not affected by the group the individuals belong to. Measurement error and misclassification bias are common examples of non-differential bias. An example of measurement error may be seen if the scales used in a study are not correctly calibrated, resulting in the incorrect recording of the weight of all animals sampled. As this form of bias affects both exposed and unexposed (or diseased and non-diseased, depending on the study type) similarly, it will reduce the strength of any associations present, and will increase the probability of a [[Random variation#Hypothesis testing and study power|type II error]].  

Non-differential bias occurs when the chance of bias is not affected by the group the individuals belong to. Measurement error and misclassification bias are common examples of non-differential bias. An example of measurement error may be seen if the scales used in a study are not correctly calibrated, resulting in the incorrect recording of the weight of all animals sampled. As this form of bias affects both exposed and unexposed (or diseased and non-diseased, depending on the study type) similarly, it will reduce the strength of any associations present, and will increase the probability of a [[Random error#Hypothesis testing and study power|type II error]].  

====Differential information bias====

====Differential information bias====

Differential bias occurs when the misclassification/measurement error for exposures or outcomes is different for the different groups being compared. This may take place through a number of stages in the investigation - common examples are incorrect results given by the participants, by the investigator or by other people involved in the study. ''Recall bias'' refers to the purposeful misrepresentation of the truth by participants (i.e. lying), whereas ''recall bias'' may be seen in relation to exposure classification for retrospective studies (where participants may have differential recollection of exposures, dependant on whether the outcome of interest was experienced).  

Differential bias occurs when the misclassification/measurement error for exposures or outcomes is different for the different groups being compared. This may take place through a number of stages in the investigation - common examples are incorrect results given by the participants, by the investigator or by other people involved in the study. ''Reporting bias'' refers to the purposeful misrepresentation of the truth by participants (i.e. lying), whereas ''recall bias'' may be seen in relation to exposure classification for retrospective studies (where participants may have differential recollection of exposures, dependant on whether the outcome of interest was experienced or not). ''Observer bias'' may result from differences in the classification of exposures or outcomes by the investigator or person assigning the classification, and can be reduced through the use of ''blinding'' techniques. For example, Boxer dogs may be more likely than other dog breeds to be diagnosed by vets as having mast cell tumours (even if they do not have them), due to a postulated breed predisposition. Differential information bias may lead to either a strengthening or a weakening of the estimated strength of association between exposure and outcome.  

 

Many of the problems of information bias can be reduced through the use of '''blinding'''.

  and may strengthen or weaken the estimated strength of association in an analytic study. For example, Boxer dogs may be more likely than other dog breeds to be diagnosed as having mast cell tumours (even if they do not have them), due to a postulated breed predisposition.

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

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