Psychiatry Research 228 (2015) 495–500
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Psychiatry Research journal homepage: www.elsevier.com/locate/psychres
Reliability and normative data of the Perceptual Aberration Scale in an Italian juvenile general population sample Livia Fornasari a, Angelo Picardi b, Marco Garzitto a,c, Antonella Gigantesco b, Michela Sala d, Manola Romanò c, Franco Fabbro a,c, Paolo Brambilla e,f,n a
Scientiﬁc Institute IRCCS “Eugenio Medea”, Italy Mental Health Unit, National Centre of Epidemiology, Surveillance and Health Promotion, Italian National Institute of Health, Rome, Italy c Department of Human Sciences (DISU), University of Udine, Udine, Italy d Department of Mental Health, Alessandria, Italy e Department of Neurosciences and Mental Health, Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico, University of Milan, Milan, Italy f Department of Psychiatry and Behavioral Sciences, University of Texas Health Science Center at Houston, TX, USA b
art ic l e i nf o
a b s t r a c t
Article history: Received 8 August 2014 Received in revised form 23 March 2015 Accepted 25 May 2015 Available online 19 June 2015
Psychometric tools, such as the Perceptual Aberration Scale (PAS), have been developed to identify people at risk to develop psychosis. This paper aims at providing an Italian version of the Perceptual Aberration Scale and its normative data for the general juvenile Italian population. The Italian version of the PAS was produced using three independent translators. It was administered to 1089 non-clinical participants, stratiﬁed into three age-groups, i.e., 8–13, 14–17 and 18–24. The Italian version of the PAS displayed good internal consistency in each age-group evaluated (i.e. Alpha Coefﬁcients: 0.90 for the 8– 13 age-group, 0.84 for the 14–17 age-group, and 0.87 for the 18–24 age-group) and the assumption of unidimensionality was corraborate. Furthermore, normative data for the three groups were collected (i.e. cut-offs: 25 for the 8–13 age-group, 21 for the 14–17 age-group and 20 for the 18–24 age-group) and an age-related difference, as the 18-24 group scored lower than the younger groups, was found. The Italian version of the PAS proved to be a reliable psychometric tool to investigate perceptual aberration during childhood, adolescence and young adulthood. & 2015 Elsevier Ireland Ltd. All rights reserved.
Keywords: Psychosis Assessment Validity Reliability Prevention
1. Introduction The term ‘schizotypy’ refers to a personality organization proposed to reﬂect vulnerability to schizophrenia or, more generally, psychosis proneness (Meehl, 1962; Chapman et al., 1995; Yung et al., 2003; Van Os et al., 2009). Indeed schizotypal features include sub-clinical psychotic symptoms like bizarre behavior, magical ideation, social withdrawal/anxiety, lack of feelings, and perceptual abnormalities (Raine, 2006). These sub-threshold psychotic experiences are common in general population (Van Os et al., 2009; Fagnani et al., 2011; Brambilla et al., 2014) and they are associated to an increased risk of developing a psychotic disorder both temporally and for experiential continuity (Linscott and Van Os, 2013). Even though only a small group of schizotypal individuals will develop the disease, as a result of the complex interaction between personality, environment and life-experiences, schizotypy may
n Corresponding author at: Department of Neurosciences and Mental Health, Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico, University of Milan, Milan, Via Francesco Sforza 35, 20122 Milano, Italy. Tel.: þ 39 02 5503.2717. E-mail address: [email protected]
http://dx.doi.org/10.1016/j.psychres.2015.05.058 0165-1781/& 2015 Elsevier Ireland Ltd. All rights reserved.
represent a dynamic continuum between psychological health, subclinical psychotic-related disorders and schizophrenia (Kwapil et al., 2008; Lenzenweger, 2010; Kwapil and Barrantes-Vidal, 2012; Ettinger et al., 2014; Picardi et al., 2014). Therefore, the early characterization of people at-risk of developing psychotic disorders is crucial to inform preventive interventions and research (Cella et al., 2013). The Wisconsin Schizotypy Scales, including the Perceptual Aberration Scale (PAS) (Chapman et al., 1978), the Magical Ideation Scale (MIS) (Eckblad and Chapman, 1983), the Physical Anedonia scale (Chapman et al., 1976) and the Revised Social Anedonia scale (Eckblad et al., 1982), have been proposed as useful instruments to identify psychosis proneness. There is wide experience in the use of these scales in non-clinical populations to detect people at high risk of developing psychotic disorders (Horan et al., 2008). The PAS was created by Chapman in 1978 to evaluate schizophrenic body image aberration. This scale was initially called Body-Image Aberration Scale, with the aim to tap aberrant features of schizophrenic experience (e.g., unclear boundaries of the body; feeling of unreality or estrangement of parts of one's body; feeling of deterioration of one's body; perception of change in the size, proportions, spatial relationship of one's body part;
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changes in the appearance of the body). After the addition of seven items covering other visual perceptual aberration experiences (e.g., ‘Sometimes when I look at things like tables and chairs, they seem strange’), the Body-Image Aberration Scale changed its name into PAS. Thus, the PAS scale, composed by 35 dichotomous True/ False items, aims at measuring aberrations and distortions in perception of the body and other objects. Indeed, disturbances of body image and unusual sensory experiences were identiﬁed as schizotypy sign in several studies. Indeed PAS scale was created to tap a positive schizotypy factor, characterized by these distortions. For instance, a study (Chapman et al., 1980) found that college students who scored at least two standard deviations above the mean on the PAS reported with greater frequency several psychotic-like experiences, such as hallucinations, aberrant beliefs, thought transmission. The PAS and the MIS present high inter-correlation (r ¼0.60–0.70) (Kwapil et al., 1997) and together deﬁne positive schizotypy which is associated with increased risk of developing psychosis (Chapman et al., 1978; Lenzenweger, 1994; Gooding et al., 2005; Kwapil et al., 2008). In a 10-year longitudinal study (Chapman et al., 1994; Kwapil et al., 2013), the individuals who scored high on MIS and PAS had higher rates of psychoses, psychotic relatives, schizotypic symptoms, and psychotic-like experiences at followup, as compared with those scoring in the normal range. The validity, internal consistency, test–retest reliability and unidimensionality of the PAS have been established by several studies carried out on university students (Fonseca-Pedrero et al., 2008; Kwapil et al., 2008; Fonseca-Pedrero et al., 2009). The aims of the present study, were to develop an Italian version of the instrument, to test its reliability, and to provide normative data for the childhood, adolescence and young adulthood in the Italian population. Although most schizotypal subjects will never develop the clinical form of psychosis, individuals with high scores in the PAS scale present a greater probability of developing schizophrenia-spectrum disorders. Thus the availability of the Italian PAS scale will allow to detect subjects with subpsychotic symptoms and personality traits that indicate greater risk for the psychotic disorder.
score ranges from 0 to 35 and it is calculated as the sum of the ‘True’ responses to all items, except four (i.e. items 6, 13, 24, 25) that are reverse-keyed. 2.3. Procedures (Italian adaptation) To obtain a valid Italian version of the instrument, we followed traditionally accepted steps in the cross-cultural adaptation of psychosocial measures (Guillemin et al., 1993). Three independent translators, who were all ﬂuent in English, produced an initial translation. Then, each translator independently reviewed the other two versions and provided comments and suggestions. Each translator included those suggestions deemed to be relevant in a second version. This process was repeated iteratively, until consensus was reached. The clarity and the acceptability of the resulting version were tested in a pilot administration until a ﬁnal Italian version of the PAS was produced. We focused our efforts on producing a good translation and refrained from performing iterative back-translation, because several authors (Harkness, 1999) have argued persuasively against back-translation for both theoretical and practical reasons, characterizing it as a sub-optimal procedure for checking translations which merely achieves linguistic and conceptual equivalence without paying attention to clarity and understandability and without taking due account of context and milieu (Bulmer, 1998). Also, a speciﬁc version of the questionnaire was produced for children aged 8– 13 years. In this version, some words and statements were simpliﬁed in order to facilitate children understand the meaning of the sentences (Table 1). 2.4. Administration The PAS was administered in the participants' classroom, in accordance with school/college organization. Only individuals who accepted to participate in the study received the questionnaire, while no information was recorded about those who did not agree to participate. None of the participants explicitly refused to complete the questionnaire. To reduce the number of missing items, the questionnaires were visually screened at the end of the session, and in case of omitted items, children were requested to complete them. Nevertheless there were some omissions; we considered omitted an item with no response or with two responses (i.e., with marked both ‘True’ response and ‘False’ one). Speciﬁcally: 25 items (0.18% of responses) were omitted in 8–13 age-group; 48 items (0.49%) in 14–17 one; 40 items (0.27%) in 18–24 one. In case of valid protocol, omitted answers were counted as absence of described experience (i.e., scored as 0). During administration, an experienced psychologist was in the classroom to resolve any doubt about the items and to ensure that participants responded to all items. The questionnaire was administered via pencil and paper to all participants. Despite group administration, each participant consigned the completed questionnaire without ﬁxed schedule. Individual compilation times were not formally recorded. 2.5. Statistical analysis
2. Methods 2.1. Participants A total of 1091 participants were enrolled in primary, secondary, high schools, and in university settings. Results of two participants were excluded from subsequent analyses because in their questionnaires there was more than 10% of omissions. Indeed a questionnaire was considered valid if there were no more than three omitted items (i.e., less than 10% of omissions). In particular, a female participant from 14 to 17 age-group (22 omissions) and a female participant from 18 to 24 one (19 omissions) were ruled out. Different cities and different types of school were selected in order to guarantee the representativeness of the sample. Random cluster sampling was performed, using the classroom as the sample unit. About half (N¼ 549, 50.5%) of participants were females, and about half (N¼536, 49.5%) were males. Due to compilation errors, information about gender was not available for four subjects (0.4%), who were excluded from gender-related analyses. Participants' age was between 8 and 24 years. They were stratiﬁed into three agegroups, i.e., 8–13 (N¼ 391, 35.8%), 14–17 (N¼279, 25.6%) and 18–24 (N¼ 421, 38.6%). After 1 month, the PAS was re-administered to 43 participants in the 18–24 agegroup (mean age: 21.571.28; gender: 38 female, 5 male) to test temporal stability. The procedure was approved by the local Ethics Committee. The questionnaires were collected anonymously. For the participants aged less than 18 years, parents provided informed consent to participate in the study, and children provided verbal assent.
2.2. Instruments A standardized form was used to collect sociodemographic information. The PAS is a 35-item self-report questionnaire, scored on a True/False scale. Its total
All analyses were conducted using SPSS for Windows, version 15.0 (SPSS Inc, 2006). The Levene's test was used to test data for homoscedasticy, and parametric analysis was used when the homoscedasticity assumption was met. One-way analysis of variance (ANOVA) with Bonferroni's post-hoc correction was used to test for differences in PAS scores between different age- groups. Student's t-test was used to test for gender-related differences in PAS scores. For each age-group, participants' scores on the PAS were expressed as means, median, variance, standard deviation (S.D.), minimum, maximum, range, interquartile range, 95% conﬁdence interval (CI) of the mean, kurtosis, and skewness. With regard to reliability, coefﬁcient Alpha was calculated to test the internal consistency of the scale for each age–group, whereas the intra-class correlation coefﬁcient (ICC) was used to examine temporal stability in the subsample of participants who completed again the PAS after a 1-month interval. In order to corroborate the assumption of unidimensionality for the PAS, principal component analyses were performed for different age–groups. In particular, principal component analyses on PAS items were used to evaluate the percentage of variance explained by the ﬁrst factor extracted and the ratio of the ﬁrst to second eigenvalue. Also, the factor structure of the PAS was compared across age-groups.
3. Results 3.1. Descriptive statistics The mean score, S.D., CI of the mean, interquartile range, and cut-off for each age-related group are reported in Table 2. Cut-off scores for each age group were set at 2 S.D. above the mean. Skewness and kurtosis values for children (8–13 years) were 0.46 ( 70.12 standard error) and 0.83 (70.25), respectively; for
L. Fornasari et al. / Psychiatry Research 228 (2015) 495–500
Table 1 Examples of the original items and the translated items.
2 3 4 5
6 7 8
9 10 11 12 13
14 15 16 17 18 19
25 26 27 28
Italian version for people older than 14 years
Italian version for the 8–13 years group
I sometimes have had the feeling that some parts of my body are not attached to the same person. Occasionally I have felt as though my body did not exist Sometimes people whom I know well begin to look like strangers. My hearing is sometimes so sensitive that ordinary sounds become uncomfortable. Often I have a day when indoor lights seem so bright that they bother my eyes.
Qualche volta ho avuto la sensazione che alcune parti del mio corpo non fossero attaccate alla stessa persona. Qualche volta ho avuto la sensazione che il mio corpo non esistesse. Certe volte persone che conosco bene cominciano a sembrarmi degli estranei. Il mio udito è a volte così sensibile che normali rumori diventano fastidiosi. Spesso ho delle giornate in cui le luci degli ambienti interni mi sembrano così forti da darmi fastidio agli occhi. Non ho mai avuto l'impressione che le mie mani e i miei piedi fossero lontani. A volte non mi sono sentito sicure che il mio corpo fosse veramente mio. Qualche volta ho avuto la sensazione di non riuscire a distinguere il mio corpo da altri oggetti intorno a me.
Qualche volta ho avuto la sensazione che alcune parti del mio corpo non fossero attaccate a me ma ad un'altra persona. Qualche volta ho avuto la sensazione che il mio corpo non esistesse. A volte le persone che conosco bene mi sembrano degli sconosciuti. A volte ci sento così bene che normali rumori diventano fastidiosi. Spesso ho delle giornate in cui le luci delle stanze mi sembrano così forti da darmi fastidio agli occhi.
My hands or feet have never seemed far away. I have sometimes felt confused as to whether my body was really my own. Sometimes I have felt that I could not distinguish my body from other objects around me. I have felt that my body and another person's body were one and the same. I have felt that something outside my body was a part of my body. I sometimes have had the feeling that my body is abnormal. Now and then, when I look in the mirror, my face seems quite different than usual. I have never had the passing feeling that my arms or legs have become longer than usual. I have sometimes felt that some part of my body no longer belongs to me. Sometimes when I look at things like tables and chairs, they seem strange. I have felt as though my head or limbs were somehow not my own. Sometimes part of my body has seemed smaller than it usually is. I have sometimes had the feeling that my body is decaying inside. Occasionally it has seemed as if my body had taken on the appearance of another person's body. Ordinary colors sometimes seem much too bright to me. Sometimes I have had a passing thought that some part of my body was rotting away. I have sometimes had the feeling that one of my arms or legs is disconnected from the rest of my body. It has seemed at times as if my body was melting into my surroundings. I have never felt that my arms or legs have momentarily grown in size.
Ho avuto la sensazione che il mio corpo e quello di un'altra persona fossero un unico stesso corpo. Ho avuto la sensazione che qualcosa fuori dal mio corpo fosse una parte del mio corpo. A volte ho avuto la sensazione che il mio corpo non fosse normale. Qualche volta, quando mi guardo nello specchio, la mia faccia sembra parecchio diversa dal solito. Non ho mai avuto la sensazione momentanea che le mie braccia o le mie gambe fossero diventate più lunghe. A volte ho avuto la sensazione che alcune parti del mio corpo non mi appartenessero più. Alcune volte, quando guardo cose come tavoli e sedie, mi sembrano strane. Ho avuto la sensazione che la mia testa o i miei arti non fossero proprio miei. Qualche volta una parte del mio corpo mi è sembrata più piccola del solito. A volte ho avuto la sensazione che il mio corpo stesse marcendo dentro. Qualche volta mi è sembrato che il mio corpo avesse preso le sembianze del corpo di un'altra persona. A volte i colori normali mi sembrano troppo brillanti.
A volte ho pensato per un momento che qualche parte A volte ho pensato per un momento che qualche del mio corpo stesse marcendo. parte del mio corpo si stesse consumando.
Qualche volta ho avuto la sensazione che una delle mie braccia o delle mie gambe fosse staccata dal resto del mio corpo. A volte mi è sembrato come se il mio corpo si stesse dissolvendo nell'ambiente. Non ho mai avuto la sensazione che le mie braccia o le mie gambe fossero momentaneamente aumentate di dimensioni. The boundaries of my body always seem I conﬁni del mio corpo mi sembrano sempre ben clear. deﬁniti. Sometimes I have had feelings that I am Qualche volta ho avuto la sensazione di essere unito united with an object near me. ad un oggetto vicino a me. Sometimes I have had the feeling that a A volte ho avuto la sensazione che una parte del mio part of my body is larger than it usually is. corpo fosse più grande del solito. I can remember when it seemed as though Ricordo di aver avuto l'impressione che uno dei miei one of my limbs took on an unusual shape. arti avesse preso una forma strana.
29 I have had the momentary feeling that my body has become misshapen. 30 I have had the momentary feeling that the things I touch remain attached to my body. 31 Sometimes I feel like everything around me is tilting. 32 I have felt as though my head or limbs were somehow not my own. 33 Sometimes part of my body has seemed smaller than it usually is.
Non ho mai avuto l'impressione che le mie mani e i miei piedi fossero lontani da me. A volte mi sembra che il mio corpo non sia proprio mio. Qualche volta ho avuto la sensazione di non riuscire a distinguere il mio corpo da altri oggetti intorno a me. Una volta mi è sembrato che il mio corpo e quello di un'altra persona fossero un unico stesso corpo. Ho avuto la sensazione che un oggetto fosse una parte del mio corpo. A volte ho avuto la sensazione che il mio corpo non fosse normale. Qualche volta, quando mi guardo allo specchio, la mia faccia sembra parecchio diversa dal solito. Non ho mai avuto la sensazione neanche per un momento che le mie braccia o le mie gambe fossero diventate più lunghe. A volte ho avuto la sensazione che alcune parti del mio corpo non fossero più mie. Alcune volte, quando guardo cose come tavoli e sedie, mi sembrano strane. Ho avuto la sensazione che la mia testa o i miei arti non fossero proprio miei. Qualche volta una parte del mio corpo mi è sembrata più piccola del solito. A volte ho avuto la sensazione che il mio corpo si stesse consumando dentro. Qualche volta mi è sembrato che il mio corpo avesse preso la forma del corpo di un'altra persona. A volte i colori normali mi sembrano troppo accesi.
Ho avuto la sensazione momentanea che il mio corpo si fosse deformato. Ho avuto la sensazione momentanea che le cose che toccavo restassero attaccate al mio corpo. A volte ho la sensazione che tutto ciò che è intorno a me stia oscillando. Certe volte devo toccarmi per essere certo di esserci ancora. Talvolta parti del mio corpo sembrano morte o irreali.
T T T T
F T T
T T T T F
T T T T T T
Qualche volta ho avuto la sensazione che una delle T mie braccia o delle mie gambe fosse staccata dal resto del mio corpo. A volte mi è sembrato come se il mio corpo si stesse T sciogliendo nell'aria. Non mi è mai sembrato che le mie braccia e le mie F gambe aumentassero di dimensioni. I conﬁni del mio corpo mi sembrano sempre precisi. Qualche volta ho avuto la sensazione di essere unito ad un oggetto vicino a me. A volte ho avuto la sensazione che una parte del mio corpo fosse più grande del solito. Ricordo di aver avuto l'impressione che una delle mie braccia o delle mie gambe avesse preso una forma strana. Ho avuto per un po' la sensazione che il mio corpo si fosse deformato. Ho avuto per un po' la sensazione che le cose che toccavo restassero attaccate al mio corpo. A volte ho la sensazione che tutto ciò che è intorno a me stia dondolando. Certe volte devo toccarmi per essere sicuro di esserci ancora. A volte parti del mio corpo sembrano morte o ﬁnte.
F T T T
T T T T T
L. Fornasari et al. / Psychiatry Research 228 (2015) 495–500
Table 1 (continued ) Original item 34 I have sometimes had the feeling that my body is decaying inside. 35 Occasionally it has seemed as if my body had taken on the appearance of another person's body.
Italian version for people older than 14 years
Italian version for the 8–13 years group
A volte mi sono chiesto se il mio corpo fosse realmente mio. A volte, per diversi giorni la sensibilità della mia vista e del mio udito è aumentata così tanto da non riuscire a stare in pace.
A volte mi sono chiesto se il mio corpo è davvero mio. A volte vedo e sento così tanto bene da non riuscire a stare in pace.
Bold character highlights differences between the two Italian versions. In the “Response” column, the answers which are scored as positive are indicated, too.
Table 2 Descriptive statistics of the PAS scores by age-group. Agegroup
N (Females %)
8–13 years 14–17 years 18–24 years
M 7 S.D.
[ 95% CI; þ95% CI]
391 (51.7%) 9.9 7 7.27 [9.2; 10.6]
278 (42.1%) 9.2 7 5.57 [8.6; 9.9]
420 (55.3%) 7.8 7 5.77 [7.2; 8.3]
CI: Conﬁdence interval of the mean; Cut-off: Cut-off score, calculated as the value two standard deviation higher than mean score for each age-group; IQR: Interquartile range; M: Mean; Max: Maximum observed value; Me: Median value; min: Minimum observed value; N: Number of available subjects; S.D.: Standard deviation.
adolescents (14–17 years) were 0.69 (7 0.15) and 0.25 ( 70.29); for young adults (18–24 years) were: 0.97 ( 70.12) and 0.53 (70.24).
According to Drasgow and Hulin (1990) the unidimensionality assumption is reasonably met if there is a dominant factor in the data. As a general guidance, the ﬁrst factor needs to account for at least 20% of the total variance (Reckase, 1979). Also, the ratio of the ﬁrst to second eigenvalue should be above 3, for unidimensionality to be considered appropriate (Morizot et al., 2009). Therefore, although only latent-trait models can provide a stringent test of the unidimensionality of a measure, this exploratory analysis corroborated the unidimensionality assumption. In the 8–13 age-group, all items displayed loadings of 0.30 or higher (corresponding to at least 9% of shared variance between a variable and a factor) on the ﬁrst factor, except for items 6, 13, 24, and 25. In the 14–17 age-group, all items displayed loadings of 0.30 or higher on the ﬁrst factor, with the exception of items 4, 6, 13, 24, and 25. In the 18–24 age-group, all items displayed loadings of 0.30 or higher on the ﬁrst factor, with the except on of items 5, 6, 12, 13, 24, and 25. Thus, the factor structures were very similar across age- groups.
4. Discussion 3.2. Age-group differences Gender-related differences were not signiﬁcant in all agerelated groups (children: males 10.32 77.63 and females 9.50 76.92; t¼ 1.11, d.f. ¼389; p ¼0.27; adolescents: males 8.96 75.42 and females 9.55 75.76; t ¼0.87, d.f. ¼ 276; p ¼0.38; young adults: males 7.917 6.35 and females 7.7075.32; t¼ 0.37, d.f. ¼414; p ¼0.71). ANOVA revealed a signiﬁcant difference in PAS score between the three age-groups, (F¼11.73, d.f. ¼2, 1086; p o0.001). The posthoc test showed that the 18–24 group scored lower than the 8–13 (p o0.001) and 14–17 (p¼ 0.01) groups. 3.3. Internal consistency and stability The internal consistency of the PAS was high, as reﬂected by coefﬁcient Alpha values of 0.90 (8–13 group), 0.84 (14–17 age group), and 0.87 (18–24 age group). Stability over a 1-month interval was found to be adequate, as indicated by an ICC value of 0.67 (95% CI 0.46–0.80). 3.4. Evaluation of scale unidimensionality Exploratory principal component analysis was performed on PAS items. In the 8–13 age-group, most communality values were satisfactory, indicating that the variables were well deﬁned by the solution. In the eigenvalue plot there was a dramatic change in the slope after the ﬁrst component, that accounted for 25% of total variance and showed an eigenvalue of 8.86 as compared with 1.68 for the second component. Similar ﬁndings were obtained in the 14–17 age-group (19.4% of variance explained, eigenvalue 6.79 vs. 2.07) and in the 18–24 age group (23% of variance explained, eigenvalue 8.05 vs. 2.40).
The purposes of present study were to develop an Italian version of the PAS, to determine its reliability, and to provide normative data for the Italian population. According to the literature, individuals with high scores on schizotypy questionnaires have a higher risk to develop schizophrenia-spectrum disorders (Chapman et al., 1994; Kwapil et al., 1997). For this reason a wide range of questionnaires have been developed to psychometrically detect people prone to psychosis. Most of the research have concentrated on adults, but to identify the process of neurodevelopment of schizophrenia, it is very important to assess schizotypy during childhood and adolescence. Indeed several other questionnaires were developed or adapted to study schizotypy also in younger people (Cyhlarova and Claridge, 2005; Raine et al., 2011; Cella et al., 2013; Debbané et al., 2013; Fonseca-Pedrero, et al.2013). To the best of our knowledge, our study is the ﬁrst to administer the PAS not only to adults or adolescents, but also to children. The PAS showed satisfactory internal consistency and stability in all age- groups. In agreement with previous literature (FonsecaPedrero, et al.2010; Miettunen and Jaaskelainen, 2010), no signiﬁcant gender differences in PAS score were found. Whereas in a previous study on adults and college students (age range 19–26) the PAS score was found not to be correlated with age (FonsecaPedrero et al., 2010), our study revealed an age-related difference, as the 18–24 group scored lower than the younger groups. A recent meta-analysis corroborated the notion that psychotic symptoms are prevalent in children as compared with adults (Kelleher et al., 2012a). Particularly psychotic symptoms were found to be quite frequent (median prevalence 17%) in younger children (9–12 years), while they were found to be less frequent (median prevalence 7.5%) in adolescents (13–18 years) and in adults (median prevalence 5%) (Van Os et al., 2009). These ﬁndings
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suggest that psychotic-like symptoms are part of normal development and become relevant from a psychopathological point of view only from adolescence (Kelleher et al., 2012b). Our results are in agreement with this notion, as the mean PAS scores were higher with decreasing age. Our exploratory principal component analysis corroborated the unidimensionality assumption for the PAS, as previously observed in large samples of young adults from different cultures (Graves and Weinstein, 2004; Horan et al., 2004; Fonseca-Pedrero et al., 2009; Winterstein et al., 2011). Substantial replication of similar factor models in different age-groups is an original observation, that suggests presence of investigated construct also in children and pre-adolescents (aged 8 to 13), as well as in adolescents (from 14 to 17 years old). Further research should use PAS and similar self-report tools to assess schizotypy in children and adolescents, following a developmental perspective. In conclusion, this study corroborates the reliability of the PAS and provided normative values for children, adolescents, and young adults drawn from the Italian general population. The availability of a reliable Italian version provides clinicians and researchers with a tool to investigate positive schizotypic features and perceptual aberration in the Italian population. Although only a small proportion of schizotypic individuals go on to develop schizophrenia as a result of complex interactions between personality, environment, and life experiences (Vollema and van den Bosch, 1995), the literature nevertheless suggests that non-clinical individuals with elevated PAS scores are at increased risk for psychosis (Chapman et al., 1994; Gooding et al., 2005). Hence, the early identiﬁcation of at-risk individuals by means of the PAS may provide the opportunity for medical surveillance and early intervention in order to prevent the subsequent development of frank psychosis or at least to lessen its impact.
Declaration of interest The authors report no declaration of interest.
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