The association of social inequality with the onset and persistence of psychotic experiences and progression along the extended psychosis phenotype: A six-year follow-up study in a community-based sample

doi:10.21203/rs.3.rs-1844285/v1

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The association of social inequality with the onset and persistence of psychotic experiences and progression along the extended psychosis phenotype: A six-year follow-up study in a community-based sample

https://doi.org/10.21203/rs.3.rs-1844285/v1

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published 22 Jan, 2023

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Purpose: This paper aims to investigate associations between early and recent indicators of socioeconomic inequality and the emergence, persistence and progression of psychotic experiences (PEs) in a longitudinal follow-up of a community-based population.

Methods: Households in the metropolitan area of Izmir, Turkey, were contacted in a multistage clustered probability sampling frame, at baseline (T₁, n = 4,011) and at 6-year follow-up (T₂, n = 2,185). Both at baseline and follow-up, PEs were assessed using Composite International Diagnostic Interview (CIDI). The associations between baseline socioeconomic features and follow-up PEs were analysed using logistic regression models. Indicators of social inequality included income, educational level, current socioeconomic status (SES), social insurance, the area resided, ethnicity, parental educational level, and SES at birth.

Results: The risk of follow-up incident PEs was significantly higher in lower education, lower SES, and slum-semi urban areas. The persistence of PEs was significantly associated with the lowest levels of education and current SES, and rural residency. Persistent PEs were significantly associated with paternal SES at birth. Progression of PEs was significantly higher among respondents with educational achievements lower than university level and lower levels of SES, who have no social insurance and who reside in slum-semi urban areas. Parental education and paternal SES at birth were not associated with the persistence of PEs.

Conclusion: Indicators of social inequality (low education, low SES, low income, poverty in the neighbourhood) were associated with the emergence and persistence of PEs and progression along the extended psychosis phenotype. The early indicators seem to have a modest life-long impact on the psychosis phenotype.

psychosis

psychotic experiences

social inequality

socioeconomic status

social class

transition

Social inequality that emerges during the functioning of modern society refers to the inequalities that are produced and observed by and within social relations. As a growing body of evidence, the effects of social inequalities on general health have become more and more observable, and it has emerged that social inequalities constitute one of the major sources of health problems, including mental health [1–3]. In the first generation of psychiatric epidemiology studies conducted during the first half of the 20th century, social characteristics such as poverty, immigration, and having a low socioeconomic status (SES) were associated with schizophrenia [4], which led to the formation of the social causation hypothesis [5]. However, studies conducted in more recent years reported more complex associations between social inequalities and psychotic disorders [6]. Also, a social drift hypothesis gained ground for pre-diagnosis and post-diagnosis deterioration of social indicators among psychotic patients [5]. However, there are powerful signs of an association between social inequalities along the lifespan and psychotic disorders [7] and the association not only covers the clinical spectrum of psychosis but also the subclinical psychotic experiences (PE) [8, 9]. Psychotic disorders, clinically relevant PEs, and subclinical PEs, which form an extended phenotype, can be regarded as poor outcomes of experienced social inequalities accumulating from pre-inception to late adulthood [8, 10, 11].

There are several reports of associations between psychotic disorders and various indicators of social inequalities, including individual level (e.g. educational level, social class, household income, employment status), neighbourhood level (e.g. poverty level of the birthplace, social disorganisation) and community level (e.g. ethnic minority status, migration) [7, 12]. Socioeconomic disadvantages at birth have been associated with an increased risk of schizophrenia and non-affective psychosis in later life [12]. In a cohort study conducted with birth records, it was shown that the increased risk of schizophrenia was associated with both the SES at birth and the low SES of the regions where individuals were born [13].

According to the psychosis continuum hypothesis, PEs are not limited to clinical psychosis [14]. An extended phenotype of psychosis includes both positive (delusions and hallucinations) and negative (social withdrawal, affective bluntness, anhedonia) symptoms, as well as clinical manifestations of psychosis [8]. PEs are common in the general population, with an estimated lifetime prevalence of 7%, but observed mostly, particularly during adolescence [9]. However, the persistence of PEs is permanent in approximately 20% and turns into a psychotic disorder in approximately 7% of cases [9, 14]. In addition, recent findings suggest that PEs occur together with the symptoms of common psychiatric disorders (e.g., depression, anxiety) [15], and the degree of co-occurrence may be affected by exposure to socio-environmental risk [16, 17].

Low income, low level of education and low social class, which are long- and short-term indicators of social inequality, affect many areas of life, mental health and even brain development from very early stages throughout life [18, 19]. There may be a relationship between social inequalities and the emergence, recurrence and persistence of PEs. Inequalities in early childhood may lead to the formation of early cognitive schemas [20] and also to the emergence of other risk factors for psychotic disorders (e.g., migration, exclusion, difficult pregnancy, birth trauma, maternal depression) [4, 18]. In adolescence and early adulthood, it may contribute to increased social exclusion and vulnerability. It is well known that there is a relationship between social exclusion, vulnerability, and clinical and subclinical psychosis [21]. For this reason, there is a need for long-term studies that will examine the relationship between inequality and the course of PEs.

In this article, we aimed to examine the associations between early and current indicators of inequality and the onset and persistence of PEs and progression along the extended psychosis phenotype in a general population sample that was re-evaluated twice in six years.

The TürkSch Study (Izmir Mental Health Survey for the Gene-Environment Interaction in Psychoses) was a prospective, longitudinal study designed mainly to screen and follow up PEs, and associated individual, family and neighbourhood-level variables in the general population [22, 23]. The sample included individuals from the Izmir metropolitan area, which is the third most urbanised area in Turkey. The TürkSch consisted of a baseline (T₁: 2008) and follow-up (T₂: 2014) assessments with approximately a six-year interval (mean follow-up time: 6.11 ± 0.94 years). This article is based on data from T₁ and T₂ assessments [22, 23].

Participants

The baseline (T₁) assessment included a sample which was randomly selected representing the wider Izmir metropolitan area using a multistage sampling procedure, stratified by urbanicity covering 11 districts and 302 neighbourhoods. T₁ was a cross-sectional assessment of mental health symptoms and help-seeking, including the extended psychosis spectrum and sociodemographic variables. Among 6000 addresses, 4011 individuals were successfully interviewed for affective and psychotic symptoms, as well as smoking, drinking and help-seeking behaviours. In 2014, six years after the baseline assessment, the addresses of all T₁ participants were revisited in person. During the second wave (T₂), 2185 participants of the first wave were re-screened for affective and psychotic symptoms, as well as smoking, drinking and help-seeking behaviours during the six-year interval. The details of the methodology of the TürkSch study and analysis of attrition during the follow-up period have been described in previous papers [22, 23].

The study was approved by the ethics committee of Ege University, both in 2008 and 2014, and written informed consent was obtained from all participants.

Psychotic Experiences and Persistence

The procedure used both at baseline (T₁) and at follow-up (T₂) assessments to identify psychotic experiences and psychotic disorders have been previously described in detail [14, 22, 23].

The time frame was lifetime at T₁, whereas it was the last six years at T₂. Hallucinations, delusions, and associated impairment/help-seeking were assessed according to the relevant sections of the Turkish version of the Composite International Diagnostic Interview (CIDI) 2.1 [24, 25]. The CIDI is a fully structured interview that can be used by both clinicians and trained interviewers [25]. CIDI was designed by the World Health Organization to be implemented in epidemiological studies of mental disorders, and it provides information about the frequency, duration and severity of symptoms, psychosocial impairment, and help-seeking due to symptoms [26].

As CIDI is a fully structured interview, it can be used by both clinicians and non-clinicians after training [25, 26]. CIDI follows a flowchart evaluating the frequency and the duration of symptoms, associated help-seeking, the history of consultations with physicians, diagnoses, and the impact on mood, social and occupational functioning. Furthermore, CIDI evaluates whether or not the symptoms are due to a somatic illness, medication, or use of alcohol or other substances [25, 26]. PEs were screened using the following modules of the CIDI 2.1: Schizophrenia and other psychotic symptoms (module G). Assessment of the positive dimension was based on 14 CIDI delusions items (G1, G2, G3, G4, G5, G7, G8, G9, G10, G11, G12, G13, G13b, and G14) and five CIDI hallucinations items (G17, G18, G20, G20C, and G21). All items were rated dichotomously, indicating presence or absence. A measure of impairment associated with PEs was defined using CIDI items G25 (duration of the PE: between 1 day and six months or more), G26, G28, G29, and G29A (level of dysfunction) and G16 and G23 (told the doctor about psychotic beliefs) [14, 22, 23].

An extended psychosis phenotype variable was constructed, including four categories using the clinical assessment results and the measure of impairment associated with PEs [22]. The psychotic disorder (PD) group included all individuals diagnosed with any DSM-IV disorder with psychotic features. The clinical PE group included individuals who had a CIDI PE leading to any of the seven CIDI impairment items but who did not have a diagnosis of PD. The subclinical PE group included individuals with a CIDI PE not leading to any distress, impairment, or help-seeking. All other individuals were included in the no psychosis category.

In order to evaluate the association between the indicators of social inequalities and the onset and persistence of PEs and progression along the extended psychosis phenotype, several categories of experiences were defined. At first, we checked the associations among the groups with no PE versus incident PE in the six-years interval. Incident PE included any endorsement of CIDI section G question from T₁ to T₂. Secondly, we compared non-persistent PEs with persistent PEs, which include individuals who endorsed any CIDI question both in T₁ and T₂. Finally, we checked for the associations between progression along the EPP during follow-up (n: 271).

Indicators of social inequality

Sociodemographic variables included sex (male and female), age categories (46–65, 31–45, 15–30 [reference 2008]), marital status (married, single, divorced [reference: 2014]), ethnicity (based on subjective information from the responded and native language at home: Turkish, non-Turkish [Kurdish, Arabic, Balkan Turks]).

Indicators of current social inequality included i) poverty based on monthly household income, ii) educational level, iii) current socioeconomic status, iv) social insurance and v) development level of the area resided. Respondents were grouped into two categories according to the monthly household income based on the 2008 data. Poverty was defined as household income less than 825 TL per month (in accordance with official numbers). Educational level was grouped into four: university, high school, elementary, and illiterate (reference year:2014). Current socioeconomic status was based on the profession of the respondent and/or the working parent in the household and recoded into four ordinal categories [27]. The first category included professionals and non-manual high employees; the second category included non-manual low employees; the third category included small proprietors and farmers, and the last category included manual workers (skilled and non-skilled). The social insurance was based on three insurance systems (for workers in the public sector, workers in the private sector, self-employed, and GreenCard [Yeşil Kart, supported by the state]). The social insurance status of the respondents was categorised into two: "any" (workers in the public sector, workers in the private sector, self-employed) and "none" (having no social insurance or having GreenCard [supported by the state for minimal health services]). The development level of the area resided was based on subjective assessment of the interviewer and categorised into three: i) urban area, ii) slum- semi-urban area and iii) village.

Indicators of early social inequality included i) maternal and paternal educational level; ii) socioeconomic status at birth (based on the occupation of the father when the respondent was born). This variable was grouped into three categories: professional, non-manual employee; small proprietors and farmers; manual workers); iii) ethnicity (based on subjective information from the respondents and native language at home) [27].

Statistics

All analyses were conducted using the software package SPSS 24.0. χ² was used for independent categorical variables, and logistic regression was used for analyses including multiple independent variables. Logistic regression was used to evaluate the associations between psychosis phenotype and indicators of social inequality. The associations were given as odds ratios (OR) with a 95% confidence interval. Our analyses included three different regression models. The first one was based on the associations between "no PE" (individuals without any psychotic experiences at T₁ and T₂) and “incident PE” (individuals without any psychotic experience at T₁ but with psychotic experiences at T₂). The second analysis was based on the associations between "non-persistent" (individuals with psychotic experiences at T₁ and without psychotic experiences at T₂) and “persistent” (individuals with PE at both T₁ and T₂). The third analysis was based on "no-progression" (individuals without an increase in severity of PE) and "progression" (individuals with increased severity of PE). In all analyses, ORs were adjusted for age and sex, and p < 0.05 were used for statistical significance.

The phenotypic status of respondents between T₁ and T₂ among the extended psychosis can be found in Fig. 1. During the follow-up period, 1403 respondents had no PE. There were 213 individuals with at least one incident PE in six years period. Three hundred twenty-six of the individuals who reported at least one PE at T₁ had no persistent PE in T₂. There were 243 individuals with at least one persistent PE. Overall, the severity of PEs in a six-year period was increased in 271 participants (with progression among EPS during follow-up).

Associations among incident PEs

Results are presented in Table 1. Incident PEs were significantly higher among 15–30 age (adjusted OR: 1.8 [95% CI: 1.3–2.7] p < 0.01), single marital status (OR: 1.62 [95% CI: 1.2–2.3] p < 0.001) however association was not significant after adjusting. There was no association between ethnicity and incident PE.

Regarding the associations between incident PE and current indicators of social inequality, there were strong associations with the level of educational achievement. The risk of incident PE was significantly higher among respondents with an educational level other than a university degree, with the highest risk in the illiterate group (adjusted OR: 2.12 [95% CI: 1-4.4] p < 0.05). There was no association between incident PEs and household poverty or social insurance. Incident PEs were associated with lower socioeconomic status with the greatest risk at the level of manual workers (adjusted OR: 1.87 [95% CI: 1.2–2.9] p < 0.01) and small proprietors and farmers (adjusted OR: 2.18 [95% CI: 1.3–3.5] p < 0.01). Incident PEs were significantly higher among the respondents who were residents in slum-semi urban areas (adjusted OR: 1.50 [95% CI: 1.1-2] p < 0.01).

Regarding associations between incident PEs and early indicators of social inequality, there was no significant association.

Table 1

Associations between indicators of social inequality and incident PEs (vs No PE) over the six-year follow-up period
	No PE (n: 1403)	Incident PE (n: 213)	Statistics
	n (%)	n (%)	OR (95% CI)	OR^a (95% CI)
Sex
Male	573 (40.8)	89 (41.8)	Ref	Ref
Female	830 (59.2)	124 (58.2)	0.9 (0.7–1.3)	0.9 (0.7–1.3)
Age
46–65	516 (36.8)	58 (27.2)	Ref	Ref
31–45	496 (35.3)	73 (34.3)	1.3 (0.9–1.9)	1.31 (0.9–1.9)
15–30	391 (27.9)	82 (38.5)	1.9 (1.3–2.7)***	1.8 (1.3–2.7)**
Marital Status
Married	1117 (79.6)	153 (71.8)	Ref	Ref
Single	242 (17.3)	54 (25.4)	1.62 (1.2–2.3)***	1.29 (0.9–1.9)
Divorced	44 (3.1)	6 (2.8)	0.99 (0.4–2.4)	1.07 (0.4–2.6)
Educational Level
University	333 (23.7)	35 (16.4)	Ref	Ref
High school	300 (21.4)	53 (24.9)	1.68 (1-2.7)*	1.73 (.1-2.7)*
Elementary	701 (50.0)	113 (53.1)	1.53 (1-2.3)*	1.78 (1.2–2.7)**
Illiterate	69 (4.9)	12 (5.6)	1.65 (0.8–3.3)	2.13 (1-4.4)*
Ethnicity
Turkish	1194 (85.1)	187 (87.8)	Ref	Ref
Non-Turkish	209 (14.9)	26 (12.2)	0.79 (0.5–1.2)	0.75 (0.5–1.1)
Household Poverty^b
No poverty	921 (67.1)	129 (60.8)	Ref	Ref
Poverty	452 (32.9)	83 (39.2)	1.31 (1-1.8)	1.33 (1-1.8)
Social Insurance
Insured	1241 (88.4)	180 (84.5)	Ref	Ref
None or Green Card	162 (11.6)	33 (15.5)	1.40 (0.9–2.1)	1.27 (0.8–1.9)
Maternal Education Level
At least high school	100 (7.2)	16 (7.6)	Ref	Ref
Elementary	761 (54.6)	114 (54.0)	0.93 (0.5–1.6)	1.03 (0.6–1.8)
Illiterate	532 (38.2)	81 (38.4)	0.95 (0.5–1.7)	1.21 (0.7–2.2)
Paternal Education Level
At least high school	210 (15.1)	33 (15.6)	Ref	Ref
Elementary	938 (67.6)	142 (67.3)	0.96 (0.6–1.4)	1.04 (0.7–1.6)
Illiterate	240 (17.3)	36 (17.1)	0.95 (0.6–1.6)	1.19 (0.7-2)
Current Socioeconomic Status
Professional and non-manual high employee	355 (25.3)	33 (15.5)	Ref	Ref
Non-manual low employee	368 (26.2)	54 (25.4)	1.57 (1-2.5)	1.52 (1-2.4)
Small proprietors and farmers	216 (15.4)	45 (21.1)	2.24 (1.4–3.6)***	2.18 (1.3–3.5)**
Manual workers	464 (33.1)	81 (38.0)	1.87 (1.2–2.9)***	1.80 (1.2–2.8)**
Socioeconomic Status at Birth
Professional, non-manual employee	399 (28.4)	54 (25.3)	Ref	Ref
Small proprietors and farmers	515 (36.7)	79 (37.1)	1.13 (0.8–1.6)	1.21 (0.8–1.8)
Manual workers	489 (34.9)	80 (37.6)	1.20 (0.8–1.7)	1.21 (0.8–1.8)
Area-level ecological environment
Urban Area	724 (53.9)	88 (43.3)	Ref	Ref
Slum-Semi-Urban Area	594 (44.2)	112 (55.2)	1.55 (1.1–2.1)***	1.50 (1.1-2)**
Village	25 (1.9)	3 (1.5)	0.98 (0.3–3.3)	1.02 (0.3–3.5)

PE: Psychotic Experiences. *p < 0.05; **p < 0.01; *** p < 0.001. ^a Adjusted for age and sex. ^b Participants who did not report their monthly income were excluded. Based on the cut-off for household poverty for the relevant year by the Turkish Statistical Institute [2008].

Associations among persistent PEs

Results are presented in Table 2. The persistence of PEs was not associated with sex, age category and ethnicity. Persistent PEs were significantly higher among divorced respondents (adjusted OR: 2.13 [95% CI: 1.09–4.2] p < 0.05). Although there was a significant association with being single, the association was not significant after adjusting for sex and age. Furthermore, the persistence of PEs was significantly associated with elementary educational level (adjusted OR: 1.74 [95% CI: 1.1.-2.9] p < 0.05).

Table 2

Associations between indicators of social inequality and persistent PEs (vs Non-persistent PE) over the six-year follow-up period
	Non-Persistent PE (n: 326)	Persistent PE (n: 243)	Statistics
	n (%) / Median (IQR)	n (%) / Median (IQR)	OR (95% CI)	OR^a (95% CI)
Sex
Male	125 (38.3)	103 (42.4)	Ref	Ref
Female	201 (61.7)	140 (57.6)	0.84 (0.6–1.2)	0.84 (0.6–1.1)
Age
46–65	97 (29.8)	65 (26.7)	Ref	Ref
31–45	105 (32.2)	76 (31.3)	1.08 (0.7–1.7)	1.09 (0.7–1.7)
15–30	124 (38.0)	102 (42.0)	1.22 (0.8–1.8)	1.22 (0.8–1.8)
Marital Status
Married	227 (69.6)	141 (58.0)	Ref	Ref
Single	82 (25.2)	80 (32.9)	1.57 (1.1–2.3)*	1.50 (1-3.4)
Divorced	17 (5.2)	22 (9.1)	2.08 (1.1–4.1)*	2.13 (1.09–4.2)*
Educational Level
University	57 (17.5)	32 (13.2)	Ref	Ref
High school	92 (28.2)	54 (22.2)	1.04 (0.6–1.8)	1.02 (0.6–1.8)
Elementary	164 (50.3)	145 (59.7)	1.57 (1-2.6)	1.74 (1.1–2.9)*
Illiterate	13 (4.0)	12 (4.9)	1.64 (0.7-4.0)	2.08 (0.8–5.3)
Ethnicity
Turkish	263 (80.7)	196 (80.7)	Ref	Ref
Non-Turkish	63 (19.3)	47 (19.3)	1.001 (0.7–1.5)	0.97 (0.6–1.5)
Household Poverty
No poverty	207 (64.5)	146 (62.1)	Ref	Ref
Poverty	114 (35.5)	89 (37.9)	1.11 (0.8–1.6)	1.12 (0.8–1.6)
Social Insurance
Insured	274 (84.1)	183 (75.3)	Ref	Ref
None or Green Card	52 (15.9)	60 (24.7)	1.72 (1.1–2.6)**	1.67 (1.1–2.6)*
Mother's Education Level at Birth
At least high school	25 (7.7)	15 (6.2)	Ref	Ref
Elementary	183 (56.7)	141 (58.3)	1.28 (0.7–2.5)	1.39 (0.7–2.8)
Illiterate	115 (35.6)	86 (35.5)	1.24 (0.6–2.5)	1.42 (0.7–2.9)
Father's Education Level at Birth
At least high school	49 (15.2)	29 (12.0)	Ref	Ref
Elementary	212 (65.8)	175 (72.3)	1.39 (0.8-2.0)	1.48 (0.9–2.5)
Illiterate	61 (18.9)	38 (15.7)	1.05 (0.6–1.9)	1.18 (0.6–2.2)
Current Socioeconomic Status
Professional and non-manual high employee	53 (16.3)	25 (10.3)	Ref	Ref
Non-manual low employee	96 (29.4)	67 (27.5)	1.47 (0.8–2.6)	1.43 (0.8–2.5)
Small proprietors and farmers	59 (18.1)	32 (13.2)	1.14 (0.6–2.2)	1.13 (0.6–2.2)
Manual workers	118 (36.2)	119 (49.0)	2.13 (1.2–3.7)***	2.12 (1.2–3.6)**
Father’s Socioeconomic Status at Birth
Professional, non-manual high employee and non-manual low employee	91 (27.9)	53 (21.8)	Ref	Ref
Small proprietors and farmers	125 (38.3)	89 (36.6)	1.22 (0.8–1.9)	1.28 (0.8-2)
Manual workers	110 (33.8)	101 (41.6)	1.57 (1-2.4)*	1.61 (1-2.5)*
Area-level ecological environment
Urban Area	161 (51.3)	103 (43.5)	Ref	Ref
Slum-Semi-Urban Area	150 (47.8)	125 (52.7)	1.3 (0.9–1.8)	1.27 (0.9–1.8)
Village	3 (0.9)	9 (3.8)	4.68 (1.2–17.7)*	4.86 (1.3–18.4)*

PE: Psychotic Experiences. *p < 0.05; **p < 0.01; *** p < 0.001. ^aAdjusted for age and sex; ^bParticipants who did not report their monthly income were excluded. Based on the cut-off for household poverty for the relevant year by the Turkish Statistical Institute [2008].

Regarding the associations between persistent PE and current indicators of social inequality, there was an association between persistent PEs and having no social insurance (adjusted OR:1.67 [95% cı:1.1–2.6] p < 0.01). Also, persistent PEs were associated with the lowest (manual workers) current socioeconomic status (adjusted OR: 2.12 [95% CI: 1.2–3.6] p < 0.01). The persistence of PEs was associated with rural residency (adjusted OR: 4.86 [95% CI: 1.4–18.4] p < 0.05).

Regarding associations between persistent PEs and early indicators of social inequality, there was no association with the paternal educational level. However, persistent PEs were significantly associated with SES at birth (adjusted OR: 1.61 [95%CI: 1-2.5] p < 0.05).

Associations based on the progression of PEs

Results are presented in Table 3. Progression of PEs was not associated with sex and ethnicity. Progression of PEs were significantly higher among 15–30 age group (adjusted OR: 1.75 [95% CI: 1.3–2.4] p < 0.001) and among single respondents (adjusted OR: 1.06 [95% CI: 0.7–1.5] p < 0.05). Although there was a significant association with being single, the association was not significant after adjusting for sex and age.

Table 3

Associations between indicators of social inequality and progression of PEs (vs no progression of PEs) over the six-year follow-up period
	No Progression during follow-up (n: 1866)	Progression among EPS during follow-up (n: 271)	Statistics
	n (%) / Median (IQR)	n (%) / Median (IQR)	OR (95% CI)	OR^a (95% CI)
Sex
Male	753 (40.4)	113 (41.7)	Ref	Ref
Female	1113 (59.6)	158 (58.3)	0.94 (0.7–1.2)	0.96 (0.7–1.2)
Age
46–65	648 (34.7)	71 (26.2)	Ref	Ref
31–45	646 (34.6)	90 (33.2)	1.27 (0.9–1.8)	1.27 (0.9–1.8)
15–30	572 (30.7)	110 (40.6)	1.75 (1.3–2.4)***	1.75 (1.3–2.4)***
Marital Status
Married	1427 (76.4)	189 (69.7)	Ref	Ref
Single	369 (19.8)	69 (25.5)	1.41 (1-1.9)*	1.06 (0.7–1.5)
Divorced	70 (3.8)	13(4.8)	1.40 (0.8–2.6)	1.52 (0.8–2.8)
Educational Level
University	412 (22.1)	39 (14.4)	Ref	Ref
High school	420 (22.5)	67 (24.7)	1.68 (1.1–2.6)*	1.70 (1.1–2.6)*
Elementary	946 (50.7)	152 (56.1)	1.69 (1.2–2.5)**	1.95 (1.3–2.9)**
Illiterate	88 (4.7)	13 (4.8)	1.56 (0.8-3)	2.01 (1–4)*
Ethnicity
Turkish	1570 (84.1)	229 (84.5)	Ref	Ref
Non-Turkish	296 (15.9)	42 (15.5)	0.97 (0.7–1.4)	0.92 (0.6–1.3)
Household Poverty
Poverty	1212 (66.3)	160 (60.4)	Ref	Ref
No Poverty	617 (33.7)	105 (39.6)	1.29 (1-1.7)	1.31 (1-1.7)*
Social Insurance
Insured	1625 (87.1)	217 (80.1)	Ref	Ref
None or Green Card	241 (12.9)	54 (19.9)	1.68 (1.2–2.3)**	1.53 (1.1–2.1)*
Mother's Education Level at Birth
At least high school	137 (7.4)	18 (6.7)	Ref	Ref
Elementary	1024 (55.3)	145 (53.9)	1.07 (0.6–1.8)	1.19 (0.7-2)
Illiterate	691 (37.3)	106 (39.4)	1.16 (0.7-2)	1.47 (0.9–2.5)
Father's Education Level at Birth
At least high school	275 (14.9)	39 (14.5)	Ref	Ref
Elementary	1250 (67.7)	184 (68.4)	1.03 (0.7–1.5)	1.12 (0.8–1.6)
Illiterate	321 (17.4)	46 (17.1)	1.01 (0.6–1.6)	1.24 (0.8-2.0)
Current Socioeconomic Status
Professional and non-manual high employee	426 (22.8)	36 (13.3)	Ref	Ref
Non-manual low employee	500 (26.8)	76 (28.0)	1.79 (1.2–2.7)**	1.71 (1.1–2.6)*
Small proprietors and farmers	295 (15.8)	50 (18.5)	2.01 (1.2–3.2)**	1.94 (1.2–3.1)**
Manual workers	645 (34.6)	109 (40.2)	2.0 (1.3-3,0)***	1.92 (1.2–2.9)***
Father’s Socioeconomic Status at Birth
Professional, non-manual employee	521 (27.9)	66 (24.3)	Ref	Ref
Small proprietors and farmers	690 (37.0)	101 (37.3)	1.15 (0.8–1.6)	1.24 (0.9–1.7)
Manual workers	655 (35.1)	104 (38.4)	1.25 (0.9–1.7)	1.26 (0.9–1.8)
Area-level ecological environment
Urban Area	944 (52.7)	111 (42.6)	Ref	Ref
Slum-Semi-Urban Area	814 (45.5)	144 (55.4)	1.50 (1.2-2.0)**	1.46 (1.1–1.9)**
Village	33 (1.8)	5 (1.9)	1.28 (0.-3.4)	1.34 (0.5–3.5)
p < 0.05; p < 0.01; ** p < 0.001. ^a Adjusted for age and sex ^bParticipants who did not report their monthly income were excluded. Based on the cut-off for household poverty for the relevant year by the Turkish Statistical Institute [2008].

Regarding the associations between the progression of PE and current indicators of social inequality, there were strong associations between the level of educational achievement. The risk was significantly higher among respondents with educational achievements other than university level (adjusted OR in the high-school group: 1.70 [95% CI: 1.1–2.6] p < 0.05; adjusted OR in the elementary group: 1.95 [95% CI: 1.3–2.9] p < 0.01; adjusted OR in the illiterate group: 2.01 [95% CI: 1–4] p < 0.05). Progression of PEs were significantly associated with household poverty (adjusted OR: 1.32 [95% CI: 1-1.7], p < 0.05), having no social insurance (adjusted OR: 1.53 [95% 1.1–2.1] p < 0.05), residency in slum-semi urban areas (adjusted OR: 1.46 [95%CI: 1.1–1.9] p < 0.01). The progression of PEs was significantly higher among respondents other than highest socioeconomic status (adjusted OR for non-manual low employee: 1.71 [95% CI: 1.1–2.6] p < 0.05; adjusted OR for small proprietors and farmers: 1.92 [95% CI:1.2-.31] p < 0.01; adjusted OR for manual workers: 1.92 [95% CI: 1.2–2.9] p < 0.001).

Regarding associations between the progression of PEs and early indicators of social inequality, there was no association with the paternal and maternal educational level and socioeconomic status at birth based on the occupation of the father.

Various indicators of social inequality are associated with both clinical and non-clinical expression of psychosis phenotype in the general population. Although there is a century-long debate about the direction of the association [4], both cross-sectional and longitudinal studies have repeatedly reported casual associations [10]. Early and current socioeconomic disadvantages lead to a transition in ultra-high-risk individuals [28]. Socioeconomic factors are reported to be the main etiologic factors in the excessive rates of psychotic disorders among immigrant groups [6]. Furthermore, social inequalities have a lifetime effect on the course and progression of psychotic disorders [7]. Not only at the clinical level but also subclinical PEs are strongly associated with lower educational levels, low income, and lower SES [9].

In this paper, we showed that indicators of early and current social inequalities were associated with the emergence, persistence, and progression of PEs in the general population. Educational achievement was strongly associated with the emergence and progression of PEs. Education represents not only current but also accumulated effects of social inequalities starting from the previous generations [29]. Our results can be regarded as the ongoing impact of educational inequality on PEs.

It has been reported that subclinical PEs are associated with ethnic minority status in western European countries (e.g. Turks in the Netherlands) [30]. In our analysis, we did not find an effect of ethnic minority status on the emergence, persistence, and progression of PEs. One of the reasons may be related to the heterogeneity of ethnic minority groups in the TürkSch; this group included individuals of Balkan and Kurdish descent who have different socio-cultural backgrounds. Another explanation might be associated with a relatively low level of discrimination among various ethnic groups in Turkey based on skin colour [31, 32].

In this paper, we used various indicators of current social inequality, including household poverty, having no social health insurance, occupation-based socioeconomic status of the respondents and area-level social disadvantage. Although poverty did not have an effect on the emergence and persistence of PEs, it increased the risk of progression of PEs. This may mean that daily income might be considered a material, psychosocial risk factor which pushes the individuals above the clinical threshold for psychosis. Poverty seems to have a more important impact on the clinical spectrum of psychosis [4]. Poverty is an outcome of various intersecting social factors. It symbolises not only long-term disadvantages but also covers short-term stress factors [29]. The paper has a follow-up period between 2008 and 2014, in which the social results of the 2008 financial crisis [33]. Thus, our results may be associated with both societal level and individual level impact of financial difficulties.

Health insurance is an indirect indicator of educational, occupational, and social achievements [29]. In Turkey, there are four different systems of health insurance, but in the case of poverty, rural background, and unemployment, the risk of having no social insurance increases [34]. Although the possession of health insurance changes from society to society, under the circumstances of modern society, having no social insurance only means accumulated psychosocial risk factors [35]. In our paper, having no social insurance was associated with the persistence and progression of PEs, which may indicate a higher risk of psychosocial risk factors. Our results may also point to the long-term disadvantage of having no insurance [29].

There is an ongoing debate about the association between low SES and psychotic disorders [4, 7]. There are reports on both social causation and social drift [5]. However, there is growing evidence of SES-related poor outcomes in various levels of psychosis, from subclinical to clinical levels [36–38]. SES mainly represents long-term social disadvantages even inherited from the past generations and can be the current outcome of disadvantages in the past [29]. In our paper, the most prominent associations were observed for the lower SES. Starting from the emergence of PEs, persistence and progression of PEs were also strongly associated with lower SES, which was most prominent in the lowest SES (manual workers). In Turkey, manual workers are the most under-skilled, undereducated, and highly exploited section of the working class [39]. Probably manual workers are at risk of high psychosocial stress, which represents the whole disadvantages of the current capitalist society in Turkey [40].

The area-level ecological environment is strongly associated with both individual-level and social-level inequalities. Poverty-related socioeconomic risk factors are concentrated in the slum areas of Turkish metropolitan cities [41]. In our results, the psychosocial risk factors associated with the incidence and progression of PEs seem to be concentrated in slum and semi-urban areas. In these regions, poverty and unemployment are higher, educational achievement is lower, and the population of these areas are excluded from the general advantages of society [41]. The most severe end of clinical psychosis, schizophrenia, seems to be associated with area-level indicators of social inequality, particularly in the most deprived areas [42]. Our results may also be related to relatively high rates of psychosis in the urban areas [43–45], but in our study, psychosis was concentrated in slum and semi-urban areas. Although slum and semi-urban areas have higher social capital, they have higher socioeconomic disadvantages in Izmir [46].

Psychosis can be a poor outcome of early social disadvantages [6, 47]. Thus, early indicators of social inequality are important for the later onset of psychosis. In our paper, we tried to investigate the early effect of socioeconomic disadvantages by checking the associations between maternal and paternal levels of education and SES at birth (based on the occupation of the father). The education level of parents and the SES at birth are meanly used as indicators of early social disadvantages [29]. These indicators are associated with sub-clinical PEs and psychotic disorders [48, 49].

In our study, there was no effect of parental education on the onset and persistence of PEs in adult life. The parental educational level can be a distant socioeconomic factor, and its impact on psychological well-being can be represented and balanced by other socioeconomic advantages and disadvantages [29]. There was only one association with the lowest socioeconomic status at birth. The paternal SES of manual workers is associated with a higher risk of persistence of PEs in adulthood.

Our results must be considered with some limitations. We have collected data at two points, and most of the indicators of social inequality were self-report. We double-checked the data and also compared income and reported SES. A recall bias may have hindered our results through the maternal and paternal educational level, paternal SES. We did not have access to administrational population data. Another limitation is the possibility of selection bias caused by attrition over time. However, the attrition analysis revealed very small effect sizes; details have been published previously [22]. And also, the attrition rate of our study is similar to previous studies with a similar design [50, 51]. Fourth, we defined the extended psychosis spectrum categories based on the presence of positive symptoms and the clinical impairment they cause. This definition is arbitrary, and the spectrum could be constructed in different ways. However, the sensitivity of CIDI is high for delusions and hallucinations, and this increases the clinical validity of our spectrum. Furthermore, the duration between the baseline and the follow-up assessments is relatively long. This long period might have limited the examination of the details of the psychotic course.

This study investigated the association between early and current indicators of social inequality and emergence, persistence and progression of psychotic experiences with a longitudinal design in a representative community-based sample. The results showed that indicators of individual-level social disadvantages (low education, low SES, low income, poverty in the neighbourhood) are associated with the onset and persistence of PEs and progression among extended psychosis phenotype. The association was particularly strong with low SES (particularly for manual workers). Furthermore, the early indicators of social disadvantage seem to have a life-long impact on psychosis phenotype. Interventions focused on decreasing social inequality in a particular society should have dramatic improvements.

PE: psychotic experiences; CIDI: Composite International Diagnostic Interview; SES: socioeconomic status.

Authors declare that they have no competing interests that are directly or indirectly related to the work submitted for publication.

Acknowledgements

The authors wish to acknowledge past and current members of the TürkSch project team, lay interviewers for data collection, and all the TürkSch participants who kindly participated in the study both in T₁ (2008) and T₂ (2014).

Funding

This work is a part of the TürkSch project, funded by the Scientific and Technological Council of Turkey (TÜBİTAK) 1001 program, project no: 107S053 and 112S476

Conflict of interest

The authors declare that they have no conflict of interest.

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The association of social inequality with the onset and persistence of psychotic experiences and progression along the extended psychosis phenotype: A six-year follow-up study in a community-based sample

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Psychotic Experiences and Persistence

Indicators of social inequality

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Associations among incident PEs

Associations among persistent PEs

Associations based on the progression of PEs

Discussion

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