Premorbid self-disorders and lifetime diagnosis in the schizophrenia spectrum: a prospective high-risk study

Authors


Abstract

Aim

The notion of a disordered self as a core disturbance of schizophrenia was proposed in many foundational texts. Recent studies, spurred by the development of the Examination of Anomalous Self-Experience (EASE), seem to indicate that self-disorders are a specific manifestation of schizophrenia vulnerability. Follow-up studies of help-seeking, prodromal and first-admission patients have demonstrated the utility of self-disorders for predicting later schizophrenia-spectrum disturbance. We wished to extend these findings by gauging the predictive value of self-disorders in a premorbid, non-clinical population at high risk for schizophrenia.

Methods

Children from the Copenhagen High-Risk Project with high-genetic risk for schizophrenia (N = 212) were assessed premorbidly (average age = 15), and diagnostically re-evaluated after 10 and 25 years. Since the EASE was not available at the time of premorbid assessment, we hypothesized that a proxy scale drawn from the Minnesota Multiphasic Personality Inventory (MMPI) could distinguish those who later developed a schizophrenia-spectrum disorder (N = 68) from those who remained healthy (N = 64). The Self-Disorder Scale comprised 32 items whose content suggested an aspect of self-disorder as measured by the EASE.

Results

Premorbid Self-Disorder Scale scores significantly predicted lifetime schizophrenia-spectrum diagnosis in the high-risk cohort. Although there was considerable item overlap between the new scale and an existing MMPI scale (psychoticism), the overlap did not account for the Self-Disorder Scale's predictive efficacy.

Conclusion

The results support the notion of self-disorders as a core vulnerability feature in schizophrenia, detectable premorbidly in those developing later schizophrenia-spectrum disorders.

Introduction

The notion of disordered self as the core trait-phenotypic disturbance of schizophrenia was proposed in all foundational texts on schizophrenia (e.g. [1-8]). In contemporary psychiatry, the notion of basic disorders of self-experience (self-disorders, SDs) in schizophrenia has only recently been rediscovered in two independent clinical, in-depth qualitative investigations of first-admission schizophrenia-spectrum patients in Denmark[9] and Norway.[10] A series of subsequent systematic empirical studies demonstrated that SDs aggregate selectively in first-admission schizophrenia and schizotypal disorders[11-13] but not in bipolar psychosis.[14, 15] SDs are detectable in populations at high-genetic risk for schizophrenia[13] and are associated with prodromal symptoms among help-seeking, non-psychotic adolescents.[16] SDs predict psychosis in clinically at-risk prodromal populations[17] as well as new cases of schizophrenia-spectrum disorders in a follow up of non-spectrum psychiatric patients 5 years after first admission.[18]

SDs affect the ‘core’ or ‘minimal’ experiential self,[19-21] that is, a structure that must be in place in order for the experience to be subjective, that is, to be someone's experience. The core self refers to a first-personal articulation of experience, typically called ‘mineness’, ‘myness’, ‘for-me-ness’ or ipseity (ipse = self, itself).[22] It is a sense of ‘I-me-myself’ that implicitly (pre-reflectively) permeates our consciousness across the flux of time, experiences and changing experiential modalities. The minimal self founds the very basic sense of identity, a condition for our ordinary experience of being a self-present, bodily, demarcated and persisting subject of experience and action.

This sense of basic selfhood, a fundamental structure of subjectivity (consciousness), appears to be challenged, unstable and oscillating in the schizophrenia-spectrum disorders, resulting in sometimes alarming and often alienating experiences, typically emerging already in childhood or early adolescence.[19] People with these disorders feel ephemeral, lacking core identity, profoundly (yet ineffably) different from others and alienated from the social world. There is a diminished sense of existing as a bodily subject, various distortions of first-person perspective with a failing sense of ‘mineness’ of the field of awareness (e.g. ‘my thoughts have no respect for me’, ‘it seems as if my thoughts were not mine’), spatialization of the experiential contents (e.g. thoughts being experienced as located, extended thing-like entities) and a deficient sense of privacy of the inner world. Simultaneously, there is a failing sense of immersion in the shared world (‘loss of common sense’) and an inadequate non-reflective (immediate) grasp of self-evident meanings (e.g. ‘why is the grass green?’), as well as a general hyperreflectivity (e.g. ‘I only live in my head’, ‘I always observe myself’.) SDs, although varying in intensity, appear to be a specific hallmark of the vulnerability for schizophrenia, thus belonging more to the trait than to the state domain of spectrum psychopathology.

Following our initial qualitative study,[9] a scale for a systematic, qualitative and quantitative semi-structured phenomenological exploration of SDs was created (Examination of Anomalous Self-Experience, EASE[23]). The EASE construction, which involved senior interdisciplinary scholars from three European countries, was based on clinical-empirical data from extensive in-depth interviews with schizophrenia patients, a review of classic and contemporary German, French and English language literature, and conceptual input from the philosophy of mind and phenomenology.[24] The EASE possesses good to excellent interrater reliability among trained interviewers.[17, 25, 26] It consists of 57 main items and explores five overlapping domains of experience: (i) stream of consciousness (experience of cognition and emotion); (ii) sense of presence/basic identity; (iii) bodily experience; (iv) sense of demarcation (‘ego boundaries’); and (v) existential reorientation (e.g. finding a new life meaning) and solipsistic experiences. The EASE exhibits high internal consistency (Cronbach's alpha above 0.80[11, 14]) and a monofactorial structure.[11, 27]

Although all studies seem to support the notion of SDs as a spectrum-specific manifestation of vulnerability, and follow-up studies of help-seeking, prodromal and first-admission patients have shown the utility of SDs for predicting later spectrum disturbance,[17, 18] there have been as yet no attempts to identify SDs and gauge their predictive value in a premorbid, not-help-seeking population at high risk for schizophrenia.

In the present study, we therefore turned to the existing data from the Copenhagen High-Risk Project (CHRP)[28] in order to explore this issue. The CHRP is the largest and longest running prospective study of children at high-genetic risk for schizophrenia. At the time of the initial assessment, subjects showed no clinical symptoms and were not seeking help for mental/emotional problems. Although the EASE instrument had not yet been developed at this time, we thought that if we could craft a rough analogue of the same content areas with existing assessments, it may hold promise for predicting later spectrum disorder. The most suitable of the available assessments is the Minnesota Multiphasic Personality Inventory (MMPI), which contains a variety of statements bearing on the first-person experience of the respondent. Several existing MMPI scales have been shown to aid the prediction of schizophrenia-spectrum outcomes.[28-30] Our interest, however, was not in replicating these successes, but in identifying an a priori set of MMPI items, selected purely on the basis of their similarity to EASE content domains, and examining the predictive properties of this analogue self-disorder scale. Our criterion would be to select any MMPI item statement that, if spontaneously presented as a complaint by the subject in an EASE interview, would motivate the EASE interviewer to explore it in-depth as a potential token of SD.

It is important to bear in mind that there are significant differences between the EASE and the MMPI. The EASE scale is mainly qualitative, requiring a high resolution, in-depth semi-structured expert interview, and the items (anomalous experiences) are first stipulated in general definitions and explicated through prototypical examples. On the other hand, the MMPI is a quantitative, superficial and self-rated report on certain aspects of experience that are presented to the subject in rather vague, everyday statements.

Methods

We elected to test the hypothesis that premorbid MMPI items analogous to the EASE scale will predict later schizophrenia-spectrum disorder with data from the CHRP.

Participants

The CHRP selected 207 children of mothers with schizophrenia and matched them with 104 children of parents without mental illness. The children (177 boys and 134 girls) ranged in age from 10 to 18 (mean age = 15.1) when they were first assessed in 1962–1964. Any children suffering from a clinically manifest mental disorder were excluded from the sample at the outset. The participants were followed up approximately 5, 10 and 25 years after the initial assessment.[31] Upon a review of both the mother and the father's psychiatric hospital records in 1980, and personal interviews with fathers conducted in 1980–1983,[32] 5 of the 104 participants originally assigned to the low-genetic risk condition were crossed over to the high-genetic risk condition due to having mothers and/or fathers who developed a schizophrenia-spectrum disorder after 1962–1964. We use these revised group assignments (212 high risk and 99 low risk) in the following analyses (see [33] for a full rationale).

Procedure

The MMPI was administered in a modified, abbreviated form during the initial 1962–1964 assessment. A total of 262 items were removed, resulting in a 304-item short form; in addition, participants sorted cards bearing these items into one of three piles, True, False and Can't Say, thus resulting in a higher number of Can't Say (missing) responses than standard paper-and-pencil versions. Details of this assessment are described elsewhere.[28] We decided against applying the traditional criteria for MMPI profile validity for several reasons: (i) the reduction in the item pool precludes calculation of the standard T-scores used to determine profile validity; (ii) the non-standard administration produced a large number of profiles with Can't Say levels traditionally considered invalid; and (iii) prior reports[28, 34] have supported the research value of including MMPI profiles which might be considered invalid in a clinical context – specifically records with elevated F (infrequency) scores among samples at high risk for psychosis. Therefore, only participants missing an MMPI assessment (N = 24) or whose MMPI record contained more than 50% Can't Say responses (i.e. more than 152 out of 304 total items; N = 15) were excluded from the analyses. The MMPI records of the remaining participants (N = 272) had a mean of 17.8% and a median of 15.1% Can't Say responses.

In order to create an MMPI scale that would be phenomenologically tied to signs of anomalous self-experience, selection of items was performed by one of us (JP) who (i) has worked extensively with Danish prodromal and first-episode schizophrenic youth; (ii) was the principal developer of the EASE interview; and (iii) is relatively unfamiliar with the MMPI in general and its predictive efficacy in this sample in particular. JP selected 56 items from the complete MMPI 566-item set for content, which could suggest a disturbance of self-experience as listed in the EASE.

From this initial a priori selection of items, another one of us (JC), with greater familiarity with the MMPI and its predictive properties in this sample, constructed the final scale. First, 24 items were discarded because they were not among the 304 MMPI items assessed in 1962–1964. Next, the remaining 32 items were subjected to reliability (internal consistency) analyses. Because the statistical program we used (the RELIABILITY command in the SPSS analysis package) does not allow for missing values, and due to the high number of missing (Can't Say) values in the MMPI data, exclusion of cases due to one or more missing items would have resulted in only 36 cases left for the reliability analyses; therefore, we decided to substitute a value of 0.5 for all missing values. In effect, this scales a Can't Say response halfway between False (scored as 0) and True (scored as 1). We believe this substitution is justifiable given the non-standard MMPI administration. After substitution of missing values, reliability analyses were run iteratively, each time discarding the item which would result in the highest Cronbach's alpha if deleted, and stopping when no further improvement was possible (see Cannon et al.[35] for use of a similar scale construction procedure). This procedure resulted in the deletion of five items from the scale with a corresponding increase of Cronbach's alpha from 0.870 to 0.879. However, upon review of these results, the researchers felt that this increase in internal consistency did not represent a substantial improvement over the initial scale selection; thus, a decision was made to revert to the original set of 32 items. These items are listed in Table 1, together with the content areas of the EASE to which each item seemed related. From this item list, the Self-Disorder Scale (SDO) was calculated by adding all items scored in the direction of pathology (all True in this case), 1 point for each item. Missing value substitution was not performed for the scale calculation; instead, the resulting raw score was prorated for the presence of missing items, and cases missing 50% or more of the scale items were assigned missing scale scores. This procedure is a slightly more conservative version of the procedure used to compensate for excessive missing values in previous analyses of this[28] and similar samples.[36, 37]

Table 1. Items composing the SDO with their EASE scale derivations
SDOEASE scale
MMPI #Item descriptionEASE #(s)Item content area(s)
  1. Note: All SDO items scored for T (True) except where indicated.
  2. EASE, Examination of Anomalous Self-Experience; MMPI, Minnesota Multiphasic Personality Inventory; SDO, Self-Disorder Scale.
 33I have had very peculiar and strange experiences.1.0–4.5(Any item)
 40Most any time I would rather sit and daydream than to do anything else.2.4, 2.6Diminished presence, hyperreflectivity
 41I have had periods of days, weeks or months when I couldn't take care of things because I couldn't ‘get going’.2.16, 2.18Diminished initiative, diminished vitality
 48When I am with people I am bothered by hearing very queer things.1.7.4, 1.10Gedankenlautwerden as voices, inability to discriminate modalities of intentionality
 50My soul sometimes leaves my body.2.8, 3.4Dissociative depersonalization, psychophysical split
 62Parts of my body often have feelings like burning, tingling, crawling, or like ‘going to sleep’.3.7Cenesthetic experiences
 74I have often wished I were a girl. (Or if you are a girl) I have never been sorry that I'm a girl. (Scored for F if female)2.9, 2.11Identity confusion, sense of change in relation to gender
102My hardest battles are with myself.1.9, 2.6, 2.7Ambivalence, hyperreflectivity, I-split
123I believe I'm being followed.02.13.06Paranoid anxiety
134At times my thoughts have raced ahead faster than I could speak them.1,3Thought pressure
142I certainly feel useless at times.2,1Diminished sense of basic self
168There is something wrong with my mind.1.0–4.5(Any item)
171It makes me uncomfortable to put on a stunt at a party even when others are doing the same sort of things.2.13.4Social anxiety
180I find it hard to make talk when I meet new people.2.12, 2.13.4Perplexity, social anxiety
182I am afraid of losing my mind.1.0–4.5(Any item)
184I commonly hear voices without knowing where they come from.1.7.4Gedankenlautwerden as voices
194I have had attacks in which I could not control my movements or speech but in which I knew what was going on around me.3,7Cenesthetic experiences
201I wish I were not so shy.2.13.4Social anxiety
211I can sleep during the day but not at night.2.4, 2.11.1Diminished presence, loss of common sense
236I brood a great deal.2,6Hyperreflectivity
278I have often felt that strangers were looking at me critically.2.13.4, 2.13.6, 5.1Social anxiety, paranoid anxiety, primary self-reference
284I am sure I am being talked about.2.13.4, 2.13.6, 5.1Social anxiety, paranoid anxiety, primary self-reference
293Someone has been trying to influence my mind.1.2, 4.4Loss of thought ipseity, passivity of mood
312I dislike having people about me.2.13.4, 2.13.6, 5.1Social anxiety, paranoid anxiety, primary self-reference
332Sometimes my voice leaves me or changes even though I have no cold.2.3.2, 3.3Unspecified depersonalization, somatic depersonalization
335I cannot keep my mind on one thing.1.1, 1.3, 1.6Thought interference, thought pressure, ruminations-obsessions
337I feel anxiety about something or someone almost all the time.2.13.5Diffuse, free-floating anxiety
338I have certainly had more than my share of things to worry about.2.6, 2.12, 2.16Hyperreflectivity, perplexity, anxiety
345I often feel as if things were not real.2.5, 5.5Derealization, feeling that world is only apparent
349I have strange and peculiar thoughts.1.0–4.5(Any item)
350I hear strange things when I am alone.1,7Gedankenlautwerden
374At periods my mind seems to work more slowly than usual.1.4, 1.11, 1.17Thought blocking, disturbance in thought initiative/intentionality, disturbance of expressive language function

Participants were given diagnostic assessments at both the 10- and 25-year follow ups; diagnoses from these assessments were reviewed in 1989 by a team of psychologists and psychiatrists and consensus DSM-III-R (Diagnostic and Statistical Manual of Mental Disorders, Third Edition, Revised) lifetime diagnoses were assigned.[31] Of the 212 high-risk participants, 32 were diagnosed with schizophrenia, 51 were assigned another diagnosis within the broad schizophrenia spectrum (non-affective psychoses, cluster A personality disorders), 43 had non-spectrum Axis I or II disorders, and 70 remained free of mental disorder. Of the 99 low-risk participants, 1 developed schizophrenia, 6 were assigned another schizophrenia-spectrum diagnosis, 33 had another Axis I or II disorder, and 57 did not develop any mental illness. The remaining participants in each group (16 high risk and 2 low risk) were unavailable at both follow ups and thus were not assigned a lifetime diagnosis.

Analysis

The study hypotheses were tested using the high-risk sample (N = 212) only, as our interest was not in testing the main effect of genetic risk (which has been amply addressed in other publications), but in uncovering the potentially additive predictive power of premorbid self-disturbance. Our analytical plan was relatively straightforward. First, we would check for possible gender and age effects on the SDO scale, which might confound predictive analyses. If no gender or age effects were found, then a one-way analysis of variance (ANOVA) would be run comparing the premorbid SDO scale scores of those who went on to incur a lifetime diagnosis in the schizophrenia spectrum (schizophrenia plus other schizophrenia-spectrum disorders) with those who were later diagnosed as no mental illness. If either gender or age effects were found, then that variable would be added as a covariate in a one-way analysis of covariance (ANCOVA). ANOVA/ANCOVA results would then be verified using logistic regression. We next planned to assess whether the number of missing values in participants' MMPI records served as a potential confound in the analysis.

We were also interested to identify possible correlations between the SDO scale (developed from an a priori content analysis) and existing MMPI scales already associated with schizophrenia-spectrum illness. For example, several scales (F, 4, 8, Wiggins' PSY (psychoticism), and Rosen's Pz) have already been shown to identify those at risk of schizophrenia in high-risk samples.[28, 37, 38]

Results

Descriptive statistics for gender and age are reported in Table 2 for each diagnostic group. Analysis of possible demographic confounds revealed no significant gender effect for SDO, but a significant negative correlation between SDO scale score and age at administration (Pearson's r = −0.202, P = 0.006).

Table 2. Descriptive statistics for gender, age and SDO by diagnostic group
VariableGroup
HR NMI (n = 64)HR spectrum (n = 68)
  1. Note: HR, high-risk cohort; NMI, no mental illness at either follow up; SDO, Self-Disorder Scale; spectrum, broad schizophrenia-spectrum diagnosis at 10-year and/or 25-year follow up.
Gender (% male/female)42%/58%60%/40%
Age at assessment (mean ± SD)15.2 ± 2.9515.6 ± 2.72
SDO score (mean ± SD)6.52 ± 4.498.47 ± 5.84

Because of this correlation, age was included as a covariant in an ANCOVA (SPSS package, UNIANOVA procedure) assessing the relationship between SDO score and lifetime diagnosis. High-risk participants with valid data for the SDO scale and lifetime diagnoses of either schizophrenia spectrum (N = 68) or no mental illness (N = 64) were included in the analysis.

The overall model was significant (F = 6.50, d.f. = 2, P = 0.002) as was the main effect for the SDO scale (F = 5.73, d.f. = 1, P = 0.018). The means and standard deviations of the SDO scores for each diagnostic group are reported in Table 2. Notably, the SDO scale means are in the expected direction: the mean premorbid SDO score for the schizophrenia-spectrum group (8.47) is 2 points higher (more features of SD) than that for the no mental illness group (6.52). Because the adequacy of the ANCOVA analyses relies on numerous parametric assumptions, we repeated the analyses using logistic regression and obtained essentially the same results: SDO score was a significant predictor of spectrum diagnosis, with a one-point increase in SDO score resulting in a 9% increase in the odds ratio for spectrum outcome.

We next investigated whether the extent of missing MMPI data varied systematically with either the independent or dependent variable or was randomly distributed with respect to these variables. There were no significant differences in the percentage of missing values by lifetime diagnostic groups (schizophrenia-spectrum diagnosis vs. no mental illness), nor was there a significant correlation between percentage of missing values and the SDO scale score.

A correlation analysis comparing the new a priori SDO scale to other scales previously associated with schizophrenia revealed moderate to high intercorrelations among these scales (see Table 3). The correlation between the SDO scale and Wiggins' PSY scale is particularly high (r = 0.864). An item-by-item comparison of these two scales is given in Table 4.

Table 3. Intercorrelations between various schizophrenia-related MMPI scales assessed premorbidly in the high-risk sample (n = 185)
MMPI scaleMMPI scale
SDOPSYF48Pz
  1. *P < 0.05; **P < 0.01; ***P < 0.001.
  2. Note: Pearson's r coefficients. Prorated raw scale scores used for all MMPI scales.
  3. 4, psychopathic deviate; 8, schizophrenia; F, infrequency; MMPI, Minnesota Multiphasic Personality Inventory; PSY, psychoticism scale; Pz, paranoid schizophrenia; SDO, Self-Disorder Scale.
SDO1     
PSY0.864***1    
F0.612***0.702***1   
40.186*0.247**0.374***1  
80.820***0.799***0.650***0.402***1 
Pz0.761***0.873***0.642***0.294***0.752***1
Table 4. Item correspondences between the SDO and the PSY
SDOPSY
MMPI #Item descriptionMMPI #Item description
  1. Note: Items listed for PSY scale are only those included in the CHRP 1962 assessment, not the complete item list. All items scored for T (True) except where indicated.
  2. MMPI, Minnesota Multiphasic Personality Inventory; PSY, psychoticism scale; SDO, Self-Disorder Scale.
   16I am sure I get a raw deal from life.
   22At times I have fits of laughing and crying that I cannot control.
 33I have had very peculiar and strange experiences. 33I have had very peculiar and strange experiences.
 40Most any time I would rather sit and daydream than to do anything else. 40Most any time I would rather sit and daydream than to do anything else.
 41I have had periods of days, weeks or months when I couldn't take care of things because I couldn't ‘get going’.  
 48When I am with people I am bothered by hearing very queer things. 48When I am with people I am bothered by hearing very queer things.
 50My soul sometimes leaves my body. 50My soul sometimes leaves my body.
 62Parts of my body often have feelings like burning, tingling, crawling, or like ‘going to sleep’.  
   66I see things or animals or people around me that others do not see.
   73I am an important person.
 74I have often wished I were a girl. (Or if you are a girl) I have never been sorry that I'm a girl. (Scored for F if female)  
102My hardest battles are with myself.  
123I believe I'm being followed.123I believe I'm being followed.
  127I know who is responsible for most of my troubles.
134At times my thoughts have raced ahead faster than I could speak them.  
142I certainly feel useless at times.  
  151Someone has been trying to poison me.
168There is something wrong with my mind.168There is something wrong with my mind.
171It makes me uncomfortable to put on a stunt at a party even when others are doing the same sort of things.  
180I find it hard to make talk when I meet new people.  
182I am afraid of losing my mind.  
184I commonly hear voices without knowing where they come from.184I commonly hear voices without knowing where they come from.
194I have had attacks in which I could not control my movements or speech but in which I knew what was going on around me.194I have had attacks in which I could not control my movements or speech but in which I knew what was going on around me.
  198I daydream very little. [Scored for F]
201I wish I were not so shy.  
211I can sleep during the day but not at night.  
236I brood a great deal.  
278I have often felt that strangers were looking at me critically.278I have often felt that strangers were looking at me critically.
284I am sure I am being talked about.284I am sure I am being talked about.
293Someone has been trying to influence my mind.293Someone has been trying to influence my mind.
  299I think that I feel more intensely than most people do.
312I dislike having people about me.312I dislike having people about me.
332Sometimes my voice leaves me or changes even though I have no cold.  
335I cannot keep my mind on one thing.  
337I feel anxiety about something or someone almost all the time.  
338I have certainly had more than my share of things to worry about.  
345I often feel as if things were not real.345I often feel as if things were not real.
  347I have no enemies who really wish to harm me. [Scored for F]
  348I tend to be on my guard with people who are somewhat more friendly than I expected.
349I have strange and peculiar thoughts.349I have strange and peculiar thoughts.
350I hear strange things when I am alone.350I hear strange things when I am alone.
374At periods my mind seems to work more slowly than usual.  
  400If given the chance I could do some things that would be of great benefit to the world.
  433I used to have imaginary companions.
  448I am bothered by people outside, on streetcars, in stores, etc., watching me.
  551Sometimes I am sure that other people can tell what I am thinking.

Our initial hypothesis that the SDO scale would predict a schizophrenia-spectrum outcome appears to be supported by the present study. However, given the high intercorrelation and item overlap between the SDO scale and the PSY scale, we needed to investigate whether it was merely the shared PSY items that accounted for the predictive efficacy of the SDO scale. In other words, is the SDO scale only predictive because it contains the PSY items? To investigate this question, we split the SDO scale into two subscales: one only containing the 15 shared items (the SDO&PSY subscale) and the other containing the 17 items unique to the SDO scale (the SDO-ONLY subscale.) The ANCOVA analyses were then rerun for each subscale in turn, with age of assessment again included as covariate. The Fs for each overall model were significant (F = 6.96, P = 0.001 for the SDO&PSY + Age model; F = 4.71, P = 0.011 for the SDO-ONLY + Age model), but only the unique items contributed significantly to the prediction of spectrum diagnosis (F = 3.49, P = NS for the SDO&PSY main effect; F = 4.32, P = 0.040 for the SDO-ONLY main effect). Thus, it appears that there is at least some element of the EASE-analogue SDO scale that is not merely duplicating previous MMPI results.

Discussion

The fact that age of first assessment was negatively correlated with the SDO scale score deserves some comment. This correlation is probably due to a selective exclusion of symptomatic, and therefore most likely older, children at the inception of the CHRP. In other words, of the children most prone to develop spectrum disorders (and thus experience a higher level of SDs), those who were relatively older at the first assessment were more likely to have entered their window of symptom onset and thus have been excluded from the sample, leaving behind the younger children who had not yet entered this window.

The main limitation of this study is a rather radical difference between the nature of the EASE and MMPI instruments, as noted in the introduction. The MMPI item contents are articulated on a superficial descriptive level because the focus is on quantitative measurement and automatic categorical decisions, and therefore more applicable to large-N studies than to in-depth studies of individual subjects. The SDO items were selected from the MMPI on the basis of a clinical judgment made by an experienced schizophrenia clinician and researcher who was the principal author of the EASE scale (JP). Positive responses to the selected MMPI items were believed to approximate points in an EASE assessment when a general complaint would be voiced by the patient and would then be followed up by an in-depth exploration of the relevant experiential domain. Our accumulated experience from performing the EASE interviews teaches us that, frequently, the patient may spontaneously verbalize a non-specific complaint (e.g. headaches, fatigue, depression, lack of concentration), which, on a more detailed in-depth exploration, turns out to signify a quite specific and a qualitatively distinct anomaly of experience (e.g. thought pressure, hyperreflectivity, sense of disembodiment, perplexity.) This particular phenomenon, especially important in early or pre-onset stages of schizophrenia, has been coined in the phenomenological psychiatric literature on schizophrenia as a ‘specific non-specificity’.[2]

However, the question as to whether the SDO MMPI scale actually taps the kind of experiential anomalies described in the EASE can only be definitively answered by exploring MMPI–EASE correlations in a sample given by both of these assessments. We are not aware of any study comparing the MMPI responses of a schizophrenia-prone sample with qualitative explorations of their anomalistic subjective experiences.

Although our design involved contrastive groups (schizophrenia spectrum vs. no mental illness) and thus did not allow us to assess specificity, these results, in conjunction with other available empirical evidence,[17, 39] are not inconsistent with the notion of SDs as a core vulnerability feature in schizophrenia,[11] detectable in both the premorbid and the prodromal stages[17] of schizophrenia. Importantly, SDs are shared by schizophrenia and schizotypal disorders, with no significant differences between these two diagnostic groups.[11, 12, 27] In the Copenhagen Linkage Study, SDs distinguished healthy high-risk individuals who exhibited few schizotypal features from healthy high-risk subjects with no schizotypal features.[40] In sum, our results, in conjunction with other SD studies, strengthen the rationale for a further exploration of the SDs as a potentially core phenotype of schizophrenia-spectrum disorders and its predictive utility in the prodromal research.[17]

Acknowledgements

The study has been supported by Grant RO1 41469 from NIMH, Bethesda, USA, to Dr J. Parnas.

Ancillary