Table 1.

Final PICO-based (Population, Intervention, Comparison, Outcome) taxonomy of reasons used to exclude articles from systematic reviews. N = not a PICO-based exclusion reason.

PICO Category	Taxonomy Code	Description
P	wrong setting	Something about the research setting was not correct. In most cases, this was an outpatient setting rather than inpatient.
	wrong previous treatment	Participants in these studies had previously received treatments that were excluded in the review article, or they were healthy when the review wanted only participants with a specific condition. For example, several reviews were of new interventions in treatment-naive patients; studies that enrolled participants already using those treatments were not included.
	wrong disease	Participants in these studies had a condition that was excluded, or it was not the same condition being evaluated in the review.
	wrong stage of disease	Participants in these studies had the desired disease but were at the wrong stage.
	wrong diagnostic process	Participants were not diagnosed using the desired criteria. For example, depression diagnosis without using DSM criteria.
	wrong comorbidity	Participants had a comorbid disease that was excluded from the review, or they did not have an included comorbidity.
	wrong age group	Participants were not in the desired age range. In most cases, the desired population was children (or adults) and the excluded study enrolled adults (or children).
	wrong sample size	The sample size was too small for inclusion in the review.
	wrong species/lab study	The study did not evaluate humans, or it was an in-vitro study.
	wrong sex	The study enrolled the wrong gender.
I	wrong duration	The duration of the intervention or the length of the study was not long enough for inclusion in the review.
	wrong intervention	The study used the wrong non-drug intervention.
	multiple interventions	The study used multiple interventions, but the review looked at only one.
	wrong drug intervention	The study used the wrong drug.
	wrong person delivering intervention	The intervention was not delivered by the person specified in the review criteria. For example, a review of nurse-delivered interventions excluded studies of home care performed by the patient.
	wrong procedure	The study did not use the desired procedure. For example, a review of laparoscopic cholecystectomy excluded studies of open cholecystectomies.
	wrong dosing/administration route	The dosing schedule was not the one desired, or the intervention was not administered via the desired route.
	insufficient intervention data	Intervention was not described in enough detail to determine the study should be included.
C	not randomized	The design of the study did not include randomization.
	not controlled	The design of the study did not include a control group.
	not a clinical trial	The study was not a clinical trial
	not an RCT	The design of the study was not a randomized controlled trial.
	not blind/double-blind	The design of the study failed to include required subject or researcher blinding.
	no placebo	The study design did not include a required placebo control.
	wrong control	The study used a control but not the one desired.
	wrong/unspecified design	The design of the study was not the one desired.
	case report/series	This was a case report or series, not a trial.
	review/comment	This was a review or comment, not a trial.
O	wrong outcome	The study used the wrong outcome.
	lack of outcome data	The study reported insufficient outcome data to extrapolate for the review.
	inadequate data analysis	The study utilized inadequate data analysis.
	lost to follow up	Too many participants were lost to follow up.
N	article not available	The staff performing the systematic review were unable to obtain the full text of the article.
	duplicate data/study	Data reported in this study were already reported in another included study.
	wrong language	The study was published in a language not accessible to the reviewers.
	article published in wrong year	The article was published prior to the range of years specified in the review criteria.
	can’t determine exclusion reason	The reason for exclusion can not be determined.