Table 1.

Characteristics of the studies included in this meta-analysis of the association between psoriasis and schizophrenia

	Eaton et al.[16]	Benros et al.[17]	Yang et al.[18]	Chen et al.[19]	Gabilondo et al.[20]
Country	Denmark	Denmark	Taiwan	Taiwan	Spain
Study design	Case-control study	Retrospective cohort study	Case-control study	Case-control study	Case-control study
Year of publication	2006	2011	2011	2012	2017
Number of participants	200,294 (7,704 cases/192,590 controls)	3.77 million	92,700 (46,350 cases/46,350 controls)	118,921 (10,811 cases/108,100 controls)	2,255,406 (7,331 cases/2,248,075 controls)
Subjects	Cases: Patients with schizophrenia were identified from the database of 15 Danish psychiatric facilities between 1981 and 1998 Controls: Sex- and age-matched controls were randomly selected from general population through the Integrated Database for Longitudinal Labor Market Research	Cases: Patients with psoriasis were identified from the Danish National Hospital Register between 1977 and 2006. The rest of the patients without diagnosis of autoimmune diseases in the register served as comparators. Comparators: The rest of the patients without diagnosis of psoriasis in the register served as comparators	Cases: Patients with schizophrenia were identified from the National Health Insurance Research Database between 1997 and 2001 Controls: Sex- and age-matched controls were randomly selected from the same underlying population	Cases: Patients with schizophrenia were identified from the National Health Insurance Research Database in 2005 Controls: Sex- and age-matched controls were randomly selected from the same underlying population	Cases: Patients with schizophrenia were identified from the database of the Basque Health System which provides universal health coverage to all residents of Basque Country Controls: The rest of the residents in the database serve as controls
Diagnosis of psoriasis	Presence of diagnostic codes of psoriasis in the database	Presence of diagnostic codes of psoriasis in the database	Presence of diagnostic codes of psoriasis in the database	Presence of diagnostic codes of psoriasis in the database	Presence of diagnostic codes of psoriasis in the database
Diagnosis of schizophrenia	Presence of diagnostic codes of schizophrenia in the database	Presence of diagnostic codes of schizophrenia in the database	Presence of diagnostic codes of schizophrenia in the database	Presence of diagnostic codes of schizophrenia in the database	Presence of diagnostic codes of schizophrenia in the database
Characteristics of participants	Not reported	Not reported	Not reported	Sex:  Cases: 45.1% female  Control: 50.5% female Geography:  Cases:  Urban 23.1%  Suburban 61.4%  Rural 12.2%  Unknown 3.2%  Control:  Urban 31.9%  Suburban 57.9%  Rural 7.8%  Unknown 2.4%	Sex:  Cases: 39.7% female  Control: 51.0% female Mean age  Cases: 48.6 years  Control: 43.9 years
Confounder adjustment	Age, sex, urbanization, socioeconomic status, and family history of schizophrenia	Age, sex, and calendar year	Age, sex, urbanization, socioeconomic status, and geographic location	Age, sex, and geographic location	Age, sex, and deprivation index
Quality assessment (Newcastle-Ottawa scale)	Selection: 3 Comparability: 2 Outcome: 3	Selection: 3 Comparability: 1 Outcome: 3	Selection: 3 Comparability: 2 Outcome: 3	Selection: 3 Comparability: 2 Outcome: 3	Selection: 3 Comparability: 1 Outcome: 3