Table 3.

Characteristics of included studies.

Study	Study design	Study setting	Participants - diagnoses	Participants - age	Participants - onset age	Outcomes	Key results - age-matched	Key results - non-age-matched
Evans et al., 1996 (14)	Cross-sectional	California United States; From the University of California Medical Center and the Community	Out of 14 DD + 253 SZ (DSM-III), aged-matched cohort of 14 DD + 50 SZ were used for comparison (the cohort is aged-matched by selecting only patients with illness onset after age 40)	Age-matched samples: DD: 66.9 (13.6) years SZ: 63.5 (8.9) years	Age-matched samples: DD: 60.4 (13.9) years SZ: 54 (9.7) years	• Clinical: BPRS, SAPS, SANS, HAMD, G-K (on premorbidity), AIMS •Neuropsychological: Attention, Verbal, Motor, Psychomotor, Learning, Memory, Abstraction, Sensory	Age-matched patients (onset after the age of 40): • DD: greater psychopathology (on BPRS); insignificant trend of fewer negative symptoms, fewer hospitalizations, lower daily neuroleptic doses • DD: lower neuropsychological impairment but not significantly • DD: less likely to be married; no significant difference in gender, years of education, premorbid adjustment (on G-K)	/
Hui et al., 2015 (6)	Cross-sectional	Hong Kong; From outpatient psychiatric units at an early intervention clinic (the Jockey Club Early Psychosis (JCEP) Project)	Out of 72 first episode DD + 157 first episode SZ (DSM-IV), aged-matched cohort of 71 DD + 71 SZ were used for comparison (propensity score matching)	Age-matched samples: DD: 41.8 (8.3) years SZ: 40.8 (8.7) years	Age-matched samples: DD: 39.4 (8.7) years SZ: 39.1 (9.3) years	• Premorbid and help-seeking characteristics: PAS, PSST • Clinical: hospitalization, comorbidities, medical illness, PANSS, SAPS, SANS, antipsychotic medication • Functioning: SOFAS, RFS • Cognitive: information, arithmetic, digit symbol, VPT, digit span, logical memory, verbal fluency	Age-matched patients: • DD: fewer hallucination (on SAPS), insignificantly more delusions (on SAPS), fewer hospitalizations, more psychiatric comorbidities (affective disorder); no difference in psychopathology (on PANSS) • No significant differences in social and occupational functioning and neurocognitive performance • DD: less premorbid schizoid and schizotypal traits (thought content), more likely to be married; no significant difference in gender, education, premorbid adjustment (on PAS)	• Cognitive functioning and gender were not significantly different • DD: more full-time employment
Marneros et al., 2012 (5)	Prospective, longitudinal follow-up of an average of 13 years following onset	Germany; From inpatient at the Department of Psychiatry, Psychotherapy and Psychosomatics at the Martin Luther University	43 DD (DSM-IV and ICD-10) + 42 PSZ (DSM-IV)	Age at index admission: DD: 51.8 (12.6) years PSZ: 41.1 (12.4) years	DD: 46.9 (13.2) years PSZ: 35.3 (13.9) years	• Clinical: PANSS • Functioning: SOFAS, GAF, DAS	/	• DD: less severe psychopathology but not significant; no first-rank symptoms, primary hallucinations, or relevant negative symptoms; no difference in delusion; less frequent and shorter hospitalization • DD: better employment, fewer early retirement due to the disorder, fewer on psychopharmacological medication; more often autarkic (living independently); lower scores in the DAS • DD: an older age of onset, broken home background; no significant difference in education.
Muñoz-Negro et al., 2015 (16)	Observational; the study combined data from 5 independent studies using compatible and similar assessment methods	Spain; From psychiatric outpatient clinics	550 psychotic disorders (373 SZ + 137 DD + 40 SA) (DSM-IV)	DD: 49.8 (14.7) years SZ: 35.9 (13.1) years SA: 46.7 (14.4) years	/	• 5 dimensions (manic, negative, depression, positive, cognitive) derived from PANSS and GAF measures	/	• DD had less positive and negative psychotic symptoms lower negative, cognitive dimensions; lower positive dimension (intermediate in SZ, higher in SA); depressive and manic dimensions higher among SA • DD had higher global functioning (lower in SZ, intermediate in SA); no gender differences but more males within SZ; more frequent incomplete primary studies, whilst complete higher studies were more frequent among SZ patients
Muñoz-Negro et al., 2017 (17)	Observational	Spain; From outpatient department at different hospitals and community mental health settings	112 psychotic disorders (67 SZ + 22 DD + 23 SA) (DSM-IV)	DD: 49.6 (12.6) years SZ: 40.4 (11.5) years SA: 44.4 (13.4) years	/	PANSS, Premorbid IQ, educational level	/	• No difference in general psychopathology, positive symptoms; SA had more severe positive symptoms than DD and SZ; SA and SZ had more severe negative symptoms than DD • No gender difference between DD and SZ; premorbid IQ and years of education were not significantly different between DD, SZ and SA
Muñoz-Negro et al., 2018 (19)	Cross-sectional comparisons, the study combined data from 3 independent studies, including both Muñoz-Negro et al. (16, 17)	Andalusia and Catalonia, Spain; From psychiatric outpatient clinics (public or private mental health services integrated or commissioned by the Spanish National Health Service)	275 patients (132 DD + 143 SZ) (DSM-IV)	DD: 50.3 (14.6) years SZ: 36.6 (11.1) years	/	•Sociodemographics (marital status, premorbid IQ, employment status, educational level) • Clinical: PANSS • Functioning: GAF	Age-adjusted patients: • DD: less severe psychopathology (on PANSS), better global functioning	On crude analysis: • DD: less severe psychopathology (on PANSS), fewer positive, negative symptoms, hallucination; no significant difference in delusion • DD: better global functioning, less work-related disability • DD: older, more frequently married; had higher estimated premorbid IQ; no gender difference in DD but more males in SZ
Peralta and Cuesta, 2016 (20)	Cross-sectional study with 1 year fup	Spain; From inpatient at the Virgen del Camino Hospital	146 DD + 114 PSZ + 244 NPSZ (DSM-IV)	DD: 49.4 (15.0) years PSZ: 40.0 (15.7) years NPSZ: 34.5 (13.1) years (DD > PSZ > NPSZ)	DD: 38.8 (14.3) years PSZ: 30.5 (13.4) years NPSZ: 23.9 (8.54) years (DD > PSZ > NPSZ)	• CASH (premorbid, SAPS, mood disorders) • 1-year fup functioning: personal care, occupation, household, social context, paid work, GAF	Age-adjusted patients: • DD: less but more severe delusions especially on jealousy, higher conviction and lower disorganization of delusional experiences, higher likelihood of major depression, chronic illness course, lack of insight, less hospitalizations • At 1-year fup, DD: better personal care and social functioning, higher numbers of paid work, poorer occupational functioning • DD: older onset age	• Of 52 variables, 40 differentiated DD from PSZ and/or NPSZ; 29 differentiated DD from both SZ, 9 differentiated DD from NPSZ, 2 differentiated DD from PSZ • PSZ was similar to NPSZ on 17 variables but similar to DD on only 7 • DD associated with the following clinical features: less but more severe delusions, especially on jealousy/somatic, higher conviction and lower disorganization of delusional experience, less hospitalization; more likelihood of major depression, higher index episode ratings of depressed mood, dysphoria, anxiety, chronic illness course, lack of insight, poorer responses to antipsychotic drugs • DD associated with the following psychosocial functioning features (at 1-year fup): better personal care and social functioning, higher numbers of paid work, poorer occupational functioning • DD associated with the following demographics: less years of education, more likely married, older, older onset age; no significant gender difference
Yassa and Suranyi-Cadotte, 1993 (18)	Longitudinal, 7-year observation period	Canada; From inpatient at the acute psychogeriatric unit	20 LOS + 7 DD with hallucinations +13 DD without hallucinations (DSM-III)	DD: 77.3 (7.2) years DD + H: 74.1 (3.8) years SZ: 78.7 (8.0) years	Age of first admission: DD: 71.3 (9.0) years DD + H: 58.9 (9.3) years SZ: 62.1 (10.7) years	• Clinical variables • Concomitant physical disorders	/	Clinical features: • LOS characterized by: bizarre delusions, AH, first-rank and negative symptoms, premorbid paranoid/schizoid personality • DD associated with: non-occurrence of negative symptoms, non-bizarre delusions, late onset of symptoms, relatively intact premorbid personality, underlying physical stratum, fewer hospitalizations and shorter duration of hospitalization but difference was insignificant • DD + H associated with: non-bizarre delusions, AH, earlier onset of symptoms, premorbid paranoid/schizoid personality Demographics: • DD: older age of onset, higher prevalence of women; no significant differences in education level and marital status

“/”, not applicable; Fup, follow-up; DD, delusional disorder; SZ, schizophrenia; SA, schizoaffective disorder; PSZ, paranoid schizophrenia; NPSZ, non-paranoid schizophrenia; LOS, late-onset schizophrenia; H, hallucinations; AH, auditory hallucination; BPRS, Brief Psychiatric Rating Scale; SAPS, Scale for the Assessment of Positive Symptoms; SANS, Scale for the Assessment of Negative Symptoms; HAMD, Hamilton Depression Rating Scale; G-K, Gittelman-Klein Premorbid Social Adjustment Scale; AIMS, Abnormal Involuntary Movement Scale; PAS, Premorbid Adjustment Scale; PSST, Assessment of Premorbid Schizoid and Schizotypal Traits; PANSS, Positive and Negative Syndrome Scale; SOFAS, Social Occupational Functioning Scale; RFS, Role Functioning Scale; VPT, Visual Patterns Test; GAF, Global Assessment of Functioning; DAS, Disability Assessment Scale; CASH, Comprehensive Assessment of Symptoms and History.