Classification of exclusion based on appropriateness:
(1) justified (appropriate)
(2) possibly justified
(3) unjustified (inappropriate)
Appropriate reasons for exclusion of a study subject:
(1) There has been a failure to obtain informed consent from subject or surrogate decision maker.
(2) The intervention has a significant risk of being harmful to the subject.
(3) Withholding the intervention or being a control has a significant risk of being harmful to the subject.
(4) The effectiveness of intervention cannot be interpreted in subject (due to comorbid disease or concurrent therapy).
(5) The subject has a form of the disease that will probably not respond to the intervention.
(6) The subject does not have the condition being studied.
(7) The subject is not at risk for outcome of interest.
Possibly appropriate reason for an exclusion:
(1) significant risk for noncompliance
(2) significant risk for failure to complete followup (dropping out or being lost)
Inappropriate reasons for an exclusion (unless these result in an appropriate reason for an exclusion):
(1) age
(2) gender
(3) racial or ethnic background
(4) religion or lack thereof
(5) language ability (written or spoken)
(6) social or economic background
(7) educational level
(8) level of intelligence (unless interferes with ability to obtain informed consent)
(9) physical ability or disability
(10) comorbid conditions
Additional factors not listed by the authors that can result in selection bias:
(1) severity of the condition (exclusion of mild disease may make a diagnostic test appear better than it is; exclusion of severe disease may make an intervention appear better)
(2) some feature that would allow investigators to determine status (if in a blinded study)
