Editing 1999: Selection Effect

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==Explanation==
 
==Explanation==
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{{incomplete|edited by Help I’m stuck in a scientific study Elaine Roberts - Please change this comment when editing this page. Do NOT delete this tag too soon.}}
  
 
The title refers to the effect in scientific fields where instead of investigating the whole population (i.e. ''all'' cancer patients or ''all'' trees) only a subset is analysed. This is common practice as the analysis of all specimens is often impractical. However, special care needs to be taken when selecting the sample to ensure that it accurately represents the general population. Otherwise the results are misleading and do not reflect reality. For example if 1000 people are asked about the numbers of cars they own but all live in a city the results cannot be generalised to the whole country. This is called the {{w|selection bias}}. If non-human subjects are studied this can be avoided by randomising the selection process, but this is not possible with humans as they cannot be forced to participate in a study against their will. For example, if people are asked to participate in a study about their political views it is likely that the responders care about politics while people with no clear opinion do not bother to respond. This is called the {{w|self-selection bias}}.
 
The title refers to the effect in scientific fields where instead of investigating the whole population (i.e. ''all'' cancer patients or ''all'' trees) only a subset is analysed. This is common practice as the analysis of all specimens is often impractical. However, special care needs to be taken when selecting the sample to ensure that it accurately represents the general population. Otherwise the results are misleading and do not reflect reality. For example if 1000 people are asked about the numbers of cars they own but all live in a city the results cannot be generalised to the whole country. This is called the {{w|selection bias}}. If non-human subjects are studied this can be avoided by randomising the selection process, but this is not possible with humans as they cannot be forced to participate in a study against their will. For example, if people are asked to participate in a study about their political views it is likely that the responders care about politics while people with no clear opinion do not bother to respond. This is called the {{w|self-selection bias}}.

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