Editing Sampling bias (section)

{{Short description|Bias in the sampling of a population}}
{{Redirect|Spotlight fallacy|the psychological effect|Spotlight effect}}
[[File:Survey-survey.svg|alt=A pie chart showing the results of a hypothetical survey, in which the question asked was "Do you enjoy responding to surveys?" The chart shows that 99.8 percent of participants said, "Yes, I love responding to surveys!" and that 0.2 percent said "No, I throw them in the trash"|thumb|An example of a biased sample in a hypothetical population survey, which asks if participants like responding to surveys, thus selecting for the individuals who were most likely to respond in the first place.|300x300px]]
In [[statistics]], '''sampling bias''' is a [[bias (statistics)|bias]] in which a sample is collected in such a way that some members of the intended [[statistical population|population]] have a lower or higher [[sampling probability]] than others. It results in a '''biased sample'''<ref>{{cite web | url = http://www.medilexicon.com/medicaldictionary.php?t=10087 | work = Medical Dictionary | title = Sampling Bias | access-date = 23 September 2009 | archive-url = https://web.archive.org/web/20160310100307/http://www.medilexicon.com/medicaldictionary.php?t=10087 |archive-date = 10 March 2016 }}</ref> of a population (or non-human factors) in which all individuals, or instances, were not equally likely to have been selected.<ref>{{cite web | url = http://medical-dictionary.thefreedictionary.com/Sample+bias | work = TheFreeDictionary | title = Biased sample | access-date = 23 September 2009 | quote = Mosby's Medical Dictionary, 8th edition }}</ref>  If this is not accounted for, results can be erroneously attributed to the phenomenon under study rather than to the method of [[sampling (statistics)|sampling]].

Medical sources sometimes refer to sampling bias as '''ascertainment bias'''.<ref>{{cite book | vauthors = Weising K |title=DNA fingerprinting in plants: principles, methods, and applications |publisher=Taylor & Francis Group |location=London |year=2005 |page=[https://archive.org/details/dnafingerprintin0000unse/page/180 180] |isbn=978-0-8493-1488-9 |url=https://archive.org/details/dnafingerprintin0000unse/page/180 }}</ref><ref>{{cite thesis | vauthors = Ramírez i Soriano A | degree = Ph.D. | title = Selection and linkage desequilibrium tests under complex demographies and ascertainment bias. | publisher = Universitat Pompeu Fabra | date = 29 November 2008 | page = 34 | url = http://www.tdx.cat/bitstream/handle/10803/7140/tars.pdf?sequence=1  }}</ref> Ascertainment bias has basically the same definition,<ref name=saem/><ref>{{cite web | url = http://www.medilexicon.com/medicaldictionary.php?t=10080 | work = Medilexicon Medical Dictionary | title = Ascertainment Bias | archive-url = https://web.archive.org/web/20160806100330/http://www.medilexicon.com/medicaldictionary.php?t=10080 | archive-date = 6 August 2016 | access-date =14 November 2009 }}</ref> but is still sometimes classified as a separate type of bias.<ref name=saem>{{cite web | vauthors = Panacek EA | date = May 2009 | title =  Error and Bias in Clinical Research | url = http://elearning.saem.org/sites/default/files/issuu/libraries/Panacek_Error_And_Bias_In_Clinical_Research_syllabus_1.pdf | archive-url = https://web.archive.org/web/20160817191133/http://elearning.saem.org/sites/default/files/issuu/libraries/Panacek_Error_And_Bias_In_Clinical_Research_syllabus_1.pdf | archive-date= 17 August 2016 | work = SAEM Annual Meeting | location = New Orleans, LA | publisher = [[Society for Academic Emergency Medicine]] | access-date = 14 November 2009 }}</ref>