In
epidemiology
Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and determinants of health and disease conditions in a defined population.
It is a cornerstone of public health, and shapes policy decisions and evide ...
, 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 closed-minded, prejudicial, or unfair. Biases can be innate or learned. People may develop biases for or against an individual, a group ...
arising from
measurement error
Observational error (or measurement error) is the difference between a measured value of a quantity and its true value.Dodge, Y. (2003) ''The Oxford Dictionary of Statistical Terms'', OUP. In statistics, an error is not necessarily a "mistake ...
. Information bias is also referred to as
observational bias
Observation is the active acquisition of information from a primary source. In living beings, observation employs the senses. In science, observation can also involve the perception and recording of data via the use of scientific instruments. The ...
and
misclassification. ''A Dictionary of Epidemiology'', sponsored by the
International Epidemiological Association
The International Epidemiological Association (IEA) is a worldwide association with more than 2000 members in over 100 different countries, who follow the aims of the association to facilitate communication amongst those engaged in research and t ...
, defines this as the following:
"1. A flaw in measuring exposure, covariate
Dependent and independent variables are variables in mathematical modeling, statistical modeling and experimental sciences. Dependent variables receive this name because, in an experiment, their values are studied under the supposition or deman ...
, 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 biases.
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
Binary may refer to:
Science and technology Mathematics
* Binary number, a representation of numbers using only two digits (0 and 1)
* Binary function, a function that takes two arguments
* Binary operation, a mathematical operation that ta ...
or
dichotomous
A dichotomy is a 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: nothing can belong simult ...
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 ordinary language, an average is a single number taken as representative of a list of numbers, usually the sum of the numbers divided by how many numbers are in the list (the arithmetic mean). For example, the average of the numbers 2, 3, 4, 7 ...
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 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 disorder which manifests as a set of related symptoms, which usually surfaces when the brain is damaged by injury or disease. The symptoms involve progressive impairments in memory, thinking, and behavior, which negatively affe ...
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.
Statisticians 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