In
epidemiology
Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and Risk factor (epidemiology), determinants of health and disease conditions in a defined population, and application of this knowledge to prevent dise ...
, information bias refers to
bias
Bias is a disproportionate weight ''in favor of'' or ''against'' an idea or thing, usually in a way that is inaccurate, closed-minded, prejudicial, or unfair. Biases can be innate or learned. People may develop biases for or against an individ ...
arising from
measurement error
Observational error (or measurement error) is the difference between a measured value of a quantity and its unknown true value.Dodge, Y. (2003) ''The Oxford Dictionary of Statistical Terms'', OUP. Such errors are inherent in the measurement pr ...
. Information bias is also referred to as
observational bias and
misclassification. ''A Dictionary of Epidemiology'', sponsored by the
International Epidemiological Association, defines this as the following:
"1. A flaw in measuring exposure, covariate, or outcome variables that results in different quality (accuracy) of information between comparison groups. The occurrence of information biases may not be independent of the occurrence of selection bias
Selection bias is the bias introduced by the selection of individuals, groups, or data for analysis in such a way that proper randomization is not achieved, thereby failing to ensure that the sample obtained is representative of the population inte ...
es.
2. Bias in an estimate arising from measurement errors."
Misclassification
Misclassification thus refers to measurement error. There are two types of misclassification in epidemiological research: non-differential misclassification and differential misclassification.
Nondifferential misclassification
Nondifferential misclassification is when all classes, groups, or categories of a variable (whether exposure, outcome, or covariate) have the same error rate or probability of being misclassified for all study subjects.
It has traditionally been assumed that in the case of
binary or
dichotomous
A dichotomy () is a partition of a set, partition of a whole (or a set) into two parts (subsets). In other words, this couple of parts must be
* jointly exhaustive: everything must belong to one part or the other, and
* mutually exclusive: nothi ...
variables nondifferential misclassification would result in an 'underestimation' of the hypothesized relationship between exposure and outcome. However, this has more recently been challenged in that results of individual studies represent a single estimate and not the
average
In colloquial, ordinary language, an average is a single number or value that best represents a set of data. The type of average taken as most typically representative of a list of numbers is the arithmetic mean the sum of the numbers divided by ...
of repeated measurements and thus can be farther (or nearer) from the
null value (i.e. zero) than the true value.
Differential misclassification
Differential misclassification occurs when the error rate or probability of being misclassified differs across groups of study subjects.
For example, the accuracy of
blood pressure
Blood pressure (BP) is the pressure of Circulatory system, circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term ...
measurement may be lower for heavier than for lighter study subjects, or a study of elderly persons may find that reports from elderly persons with
dementia
Dementia is a syndrome associated with many neurodegenerative diseases, characterized by a general decline in cognitive abilities that affects a person's ability to perform activities of daily living, everyday activities. This typically invo ...
are less reliable than those without dementia. The effect(s) of such misclassification can vary from an overestimation to an underestimation of the true value.
Statistician
A statistician is a person who works with Theory, theoretical or applied statistics. The profession exists in both the private sector, private and public sectors.
It is common to combine statistical knowledge with expertise in other subjects, a ...
s have developed methods to adjust for this type of bias, which may assist somewhat in compensating for this problem when known and when it is quantifiable.
References
Further reading
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{{Biases
Bias