Selection bias

selection effectselectionbiasselection effectssampling biasattrition biasbiasesdata selectiondropoutexclusion 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 ensuring that the sample obtained is not representative of the population intended to be analyzed.wikipedia
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Response rate (survey)

response rateresponse ratesNon-response
It includes dropout, nonresponse (lower response rate), withdrawal and protocol deviators.

Public health intervention

interventionhealth interventioninterventions
Different loss of subjects in intervention and comparison group may change the characteristics of these groups and outcomes irrespective of the studied intervention.

Impact event

impactmeteorite impactasteroid impact
An example is the past impact event record of Earth: if large impacts cause mass extinctions and ecological disruptions precluding the evolution of intelligent observers for long periods, no one will observe any evidence of large impacts in the recent past (since they would have prevented intelligent observers from evolving).

Global catastrophic risk

existential riskdoomsdayGlobal catastrophic risks
Astronomical existential risks might similarly be underestimated due to selection bias, and an anthropic correction has to be introduced.


An assessment of the degree of selection bias can be made by examining correlations between exogenous (background) variables and a treatment indicator.

Regression analysis

regressionmultiple regressionregression model
However, in regression models, it is correlation between unobserved determinants of the outcome and unobserved determinants of selection into the sample which bias estimates, and this correlation between unobservables cannot be directly assessed by the observed determinants of treatment.

Criticism of Amnesty International

independent report
Criticism of Amnesty International (AI) includes claims of selection bias, as well as ideology and foreign policy bias against either non-Western countries or Western-supported countries.

Average human height by country

List of average human height worldwideAverage height around the worldcontemporary national averages

Randomized controlled trial

randomized controlled trialsrandomized clinical trialrandomized control trial
The randomness in the assignment of subjects to groups reduces selection bias and allocation bias, balancing both known and unknown prognostic factors, in the assignment of treatments.

Malmquist bias

effectMalmquist effect
In statistics, this bias is referred to as a selection bias and affects the survey results in a brightness limited survey, where stars below a certain apparent brightness are not included.

Chloroplast DNA

plastomecpDNAchloroplast genome
Since then, hundreds of chloroplast DNAs from various species have been sequenced, but they are mostly those of land plants and green algae—glaucophytes, red algae, and other algae groups are extremely underrepresented, potentially introducing some bias in views of "typical" chloroplast DNA structure and content.

Cross-validation (statistics)

cross-validationcross validationLeave-one-out cross-validation
The goal of cross-validation is to test the model's ability to predict new data that was not used in estimating it, in order to flag problems like overfitting or selection bias and to give an insight on how the model will generalize to an independent dataset (i.e., an unknown dataset, for instance from a real problem).

Impact evaluation

impactimpact analysis
There are five key principles relating to internal validity (study design) and external validity (generalizability) which rigorous impact evaluations should address: confounding factors, selection bias, spillover effects, contamination, and impact heterogeneity.

Energy medicine

spiritual healingspiritual healerenergy healing
The theoretical basis of healing has been criticised as implausible, research and reviews supportive of energy medicine have been faulted for containing methodological flaws and selection bias, and positive therapeutic results have been determined to result from known psychological mechanisms.

High-dose chemotherapy and bone marrow transplant

HDC-ABMTHDC/BMTHigh-dose chemotherapy
This selection bias makes the treatment look better, because candidates who would have fared better under any condition were selected.

Berkeley Earth

Berkeley Earth Surface TemperatureBerkeley Earth'',Muller et al.
The study addressed scientific concerns including urban heat island effect, poor station quality, and the risk of data selection bias.

Allocation concealment

concealment of allocation
Studies with poor allocation concealment (or none at all) are prone to selection bias.

Alex Berenson

data that fits his narrative, and falling victim to selection bias via his use of anecdotes

Star system

multiple star systemtriple starmultiple systems
However, because of selection effects, knowledge of these statistics is very incomplete.

Length time bias

length-biased sampling
It is a form of selection bias, a statistical distortion of results that can lead to incorrect conclusions about factual data.