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In statistics, sampling bias is a bias in which a sample is collected in such a way that some members of the intended population are less likely to be included than others. It results in a biased sample, a non-random sample〔(Medical Dictionary - 'Sampling Bias' ) Retrieved on September 23, 2009〕 of a population (or non-human factors) in which all individuals, or instances, were not equally likely to have been selected.〔(TheFreeDictionary – biased sample ) Retrieved on 2009-09-23. Site in turn cites: Mosby's Medical Dictionary, 8th edition.〕 If this is not accounted for, results can be erroneously attributed to the phenomenon under study rather than to the method of sampling. Medical sources sometimes refer to sampling bias as ascertainment bias.〔Page 34 in: (Selection and linkage desequilibrium tests under complex demographies and ascertainment bias ) Francesc Calafell i Majó, Anna Ramírez i Soriano. July 2008〕 Ascertainment bias has basically the same definition,〔〔(medilexicon Medical Dictionary - 'Ascertainment Bias' ) Retrieved on November 14, 2009〕 but is still sometimes classified as a separate type of bias.〔(Panacek: Error in research ) Society for Academic Emergency Medicine. Retrieved on November 14, 2009〕 ==Distinction from selection bias== Sampling bias is mostly classified as a subtype of selection bias,〔(Dictionary of Cancer Terms – Selection Bias ) Retrieved on September 23, 2009〕 sometimes specifically termed sample selection bias, but some classify it as a separate type of bias. A distinction, albeit not universally accepted, of sampling bias 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. However, selection bias and sampling bias are often used synonymously. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Sampling bias」の詳細全文を読む スポンサード リンク
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