selection bias

• Selection Bias

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Epidemiology - Selection bias

1 Selection bias occurs when study subjects are selected or become part

of the study as a result of a third, unmeasured variable which is

associated with both the exposure and outcome of interest


Fraud in parapsychology - Selection bias and meta-analysis

1 Selection bias|Selective reporting has been offered by critics as an

explanation for the positive results reported by parapsychologists


Internal validity - Selection bias

1 Selection bias refers to the problem that, at pre-test, differences between groups exist that

may interact with the independent variable and thus be 'responsible' for the observed

outcome. Researchers and participants bring to the experiment a myriad of characteristics,

some learned and others inherent. For example, sex, weight, hair, eye, and skin color, personality, mental capabilities, and physical abilities, but also attitudes like motivation or

willingness to participate.


Medical screenings - Selection bias

1 Selection bias may also make a test look better than it really is. If a test is more available to young and healthy people (for instance if people have to

travel a long distance to get checked) then fewer people in the

screening population will have negative outcomes than for a

random sample, and the test will seem to make a positive difference.


Impact evaluation - Selection bias

1 This is known as selection bias (Rossi

et al., 2004)


Impact evaluation - Selection bias

1 However, random assignment designs are not safe from selection bias which is induced by attrition

(Rossi et al., 2004).


Selection bias

1 If the selection bias is not taken into account, then some conclusions of

the study may not be accurate.


Selection bias - Types

1 There are many types of possible selection bias,

including:


Selection bias - Sampling bias

1 PMID 9504213.[http://www.cs.nyu.edu/~m

ohri/postscript/bias.pdf Sample Selection Bias Correction Theory] Corinna Cortes, Mehryar Mohri,

Michael Riley, and Afshin Rostamizadeh


Selection bias - Sampling bias

1 A distinction of sampling bias (albeit not a universally accepted one) is that it

undermines the external validity of a test (the ability of its results to be generalized to the rest of the population), while selection bias

mainly addresses internal validity for differences or similarities found in the sample at hand. In this sense, errors occurring in the

process of gathering the sample or cohort cause sampling bias, while errors in any process thereafter cause selection bias.


Selection bias - Attrition

1 Attrition bias is a kind of selection bias caused by attrition (loss of participants), discounting trial

subjects/tests that did not run to completion


Selection bias - Observer selection

1 Astronomical existential risks might similarly be underestimated due to

selection bias, and an anthropic correction has to be introduced.


Selection bias - Avoidance

1 An informal assessment of the degree of selection bias can be made by examining correlations between exogenous (background) variables

and a treatment indicator


Self-selection bias

1 In statistics, 'self-selection bias' arises in any situation in which

individuals select themselves into a group (sociology)|group, causing a biased sample with nonprobability sampling. It is commonly used to describe situations where the characteristics of the people which cause them to select themselves

in the group create abnormal or undesirable conditions in the group.


Self-selection bias

1 Self-selection bias is a major problem in research in sociology, psychology,

economics and many other social sciences.Ziliak, S.T., McCloskey, D.N


Self-selection bias

1 While the effects of self-selection bias are closely related to those of selection

bias, the problem arises for rather different reasons; thus there may be a

purposeful intent on the part of respondents leading to self-selection bias

whereas other types of selection bias may arise more inadvertently, possibly

as the result of mistakes by those designing any given study.


Self-selection bias - Explanation

1 Self-selection bias causes problems for research about programs or

products. In particular, self-selection makes it difficult to Program

evaluation|evaluate programs, to determine whether the program has some effect, and makes it difficult to

do market research.


Biased sample - Distinction from selection bias

1 In this sense, errors occurring in the process of gathering the sample or cohort cause sampling bias, while errors in any process thereafter

cause selection bias.


Biased sample - Distinction from selection bias

1 However, selection bias and sampling bias are often used

synonymously.[http://books.google.dk/books?

id=EBq63uyt87QCprintsec=frontcoversource=gbs_navlinks_s#v=onepageq=sometime

s%20used%20synonymouslyf=false Wallace/Maxcy-Rosenau-Last public health

preventive medicine (page 21)] 15ed, illustrated. By Robert B. Wallace. ISBN 0-07-

144198-0, ISBN 978-0-07-144198-8https://store.theartofservice.com/the-selection-bias-toolkit.html

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