Difference between revisions of "Survival bias"

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This bias occurs when survivors of a highly lethal disease are more likely to enter a study than other cases.
  
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Example: let's suppose we study the role of age as a potential risk factor for viral haemorrhagic fever (VHF), and that the study includes only those who are still alive at the time of the study. If older age is associated with VHF death, this will decrease the proportion of cases over a certain age in the study, and consequently underestimate the odds ratio. This is illustrated in the following table:
  
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{| class="wikitable" style="text-align:center;"
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|- style="font-weight:bold; text-align:left;"
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! style="vertical-align:middle;" | Age group
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! style="vertical-align:middle;" | VHF survivors
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! style="vertical-align:middle;" | VHF deaths
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! style="vertical-align:middle;" | Total cases
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! style="vertical-align:middle;" | Controls
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! style="text-align:center; background-color:#F0F8FF;" | ORs
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! style="text-align:center; background-color:#F0F8FF;" | ORtt
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|-
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| style="vertical-align:middle; font-style:italic; text-align:left;" | < 50 years
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| style="vertical-align:middle;" | 60
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| style="vertical-align:middle;" | 80
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| style="vertical-align:middle;" | 140
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| style="vertical-align:middle;" | 50
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| style="background-color:#F0F8FF;" | 1.5
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| style="background-color:#F0F8FF;" | 2.3
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|-
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| style="vertical-align:middle; font-style:italic; text-align:left;" | ≥ 50 years
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| style="vertical-align:middle;" | 40
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| style="vertical-align:middle;" | 20
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| style="vertical-align:middle;" | 60
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| style="vertical-align:middle;" | 50
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| style="background-color:#F0F8FF;" | ref.
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| style="background-color:#F0F8FF;" | ref.
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|-
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| style="vertical-align:middle; text-align:left;" | Total
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| style="vertical-align:middle;" | 100
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| style="vertical-align:middle;" | 100
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| style="vertical-align:middle;" | 200
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| style="vertical-align:middle;" | 100
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| style="background-color:#F0F8FF; text-align:left;" |
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| style="background-color:#F0F8FF; text-align:left;" |
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|- style="text-align:left; vertical-align:middle;"
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| colspan="7" | ORs = OR with all surviving cases
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|- style="text-align:left; vertical-align:middle;"
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| colspan="7" | ORtt = OR with all cases
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|}
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<div style="display: inline-block; width: 25%; vertical-align: top; border: 1px solid #000; background-color: #d7effc; padding: 10px; margin: 5px;">
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'''FEM PAGE CONTRIBUTORS 2007'''
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;Contributor
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:Arnold Bosman
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</div>
 
[[Category:Selection bias and case-control studies]]
 
[[Category:Selection bias and case-control studies]]

Latest revision as of 13:55, 12 April 2023

This bias occurs when survivors of a highly lethal disease are more likely to enter a study than other cases.

Example: let's suppose we study the role of age as a potential risk factor for viral haemorrhagic fever (VHF), and that the study includes only those who are still alive at the time of the study. If older age is associated with VHF death, this will decrease the proportion of cases over a certain age in the study, and consequently underestimate the odds ratio. This is illustrated in the following table:

Age group VHF survivors VHF deaths Total cases Controls ORs ORtt
< 50 years 60 80 140 50 1.5 2.3
≥ 50 years 40 20 60 50 ref. ref.
Total 100 100 200 100
ORs = OR with all surviving cases
ORtt = OR with all cases


FEM PAGE CONTRIBUTORS 2007

Contributor
Arnold Bosman
Retrieved from "https://femwiki.org/index.php?title=Survival_bias&oldid=1738"

Contributors