***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Prior research has suggested that the latent structure of the schizotypy construct ( P. E. Meehl , 1990 ) may be qualitative in nature and have a low base rate ( L. Korfine & M. F. Lenzenweger , 1995 ; M. F. Lenzenweger & L. Korfine , 1992 ) . These studies relied on the application of maximum covariance analysis ( MAXCOV ) to 8 true-false format items from a schizotypy measure . The current study sought to examine the robustness of those prior findings through MAXCOV analysis of fully quantitative measures of schizotypy . Measures of perceptual aberration , magical ideation , and referential thinking were analyzed using MAXCOV in a sample of 429 persons . The results of these analyses strongly support a latent taxonic structure for schizotypy and a low base rate for the schizotypy taxon . Furthermore , the members of the putative taxon reveal an increased level of deviance on a psychometric measure known to be associated with schizophrenia liability . The possibility that the dichotomous item format of those items analyzed previously with MAXCOV lead to spurious pseudotaxonicity is greatly diminished in light of these results Classical descriptions of mania subtypes extend back to Kraepelin ; however , in marked contrast to the study of depression subtypes , validation of mania subtypes by multivariate statistical methods has seldom been attempted . We applied Grade of Membership ( GOM ) analysis to the rated clinical features of 327 in patients with DSM-III-R mania diagnoses . GOM is a type of latent structure multivariate analysis , which differs from others of this type in making no a priori distributional assumptions about groupings . We obtained 5 GOM Pure Types with good face validity . The major Kraepelinian forms of “ hypomania , ” “ acute mania , ” “ delusional mania , ” and “ depressive or anxious mania ” were vali date d. The major new finding is of two mixed mania presentations , each with marked lability of mood . The first of these displayed a dominant mood of severe depression with labile periods of pressured , irritable hostility and paranoia , and the complete absence of euphoria or humor . The second mixed mania Pure Type displayed a true , incongruous mixture of affects : periods of classical manic symptoms with euphoria , elation , humor , gr and iosity , psychosis , and psychomotor activation , switching frequently to moderately depressed mood with pressured anxiety and irritability . This multivariate analysis vali date d classical clinical descriptions of the major subtypes of mania . Two distinct forms of mixed manic episodes were identified . DSM-III-R criteria did not reliably identify either of these two natural groups of mixed bipolar patients . As occurs in depression , this clinical heterogeneity of mania may influence response to drug treatments Objective : To describe patients included in the European Mania in Bipolar Longitudinal Evaluation of Medication ( EMBLEM ) study and to assess and clinical ly vali date the presence of clinical subtypes of patients with acute mania P.E. Meehl 's model ( 1962 , 1990 ) of schizotypy and the development of schizophrenia implies that the structure of liability for schizophrenia is dichotomous , hypothesizing that a " schizogene " determines one 's membership in a latent class ( or taxon ; P.E. Meehl & R. R. Golden , 1982 ) . The present study sought to replicate earlier findings concerning the taxonic latent structure and general population base rate of schizotypy ( M. F. Lenzenweger & L. Korfine , 1992 ) . P.E. Meehl 's ( 1973 ; P.E. Meehl & R. R. Golden , 1982 ) MAXCOV-HITMAX taxometric analytic procedures were applied to a subset of items from the Perceptual Aberration Scale ( PAS ; L. J. Chapman , J. P. Chapman , & M. L. Raulin , 1978 ) , a prominent psychometric index of schizotypy , derived from a new r and omly ascertained non clinical university sample ( N = 1,646 ) . Consistent with the authors ' previous results as well as Meehl 's conjectures , the data strongly suggest that schizotypy , as assessed by the PAS , is taxonic at the latent level with a low general population taxon base rate ( i.e. , < .10 ) . Moreover , individuals falling within the putative schizo-taxon underlying the PAS present greater levels of schizotypic phenomenology than nontaxon members . The taxometric analysis of the psychological trait of femininity also reveals that the MAXCOV-HITMAX procedure can detect a latent dimension , when one is hypothesized to exist , and the procedure does not appear to generate " spurious " evidence for taxonicity as a function of the psychometric format ( e.g. , true-false ) of the data under analysis . The statistical implication of a taxonic entity occurring at a low base is discussed with respect to results obtained using the MAXCOV-HITMAX technique BACKGROUND Several studies have found an association between duration of untreated psychosis ( DUP ) and clinical outcomes . However , there is inconsistency concerning the association between outcome on negative symptoms and DUP with some studies having found a correlation between DUP and negative symptoms , while other studies did not find such an association . OBJECTIVE The aim of the present study was to investigate the role of heterogeneity associated with the relationship between DUP and negative symptoms in a sample of first episode psychosis ( FEP ) patients from a multicentre treatment study and a replication sample of subjects from a specialized service in a different jurisdiction . METHOD FEP patients ( n=116 ) treated in specialized programs in two medium sized and one large urban centre were evaluated . Latent class regression was employed to simultaneously classify respondents and estimate the effect of DUP on negative symptoms after one year . The process was repeated on 59 consecutive FEP patients in a specialized service in Montreal . RESULTS The final model reflected three distinct sub-groups with different associations between DUP and negative symptoms : ( a ) for one fourth of the subjects there was a positive association between DUP and negative symptoms , indicating that long DUP was associated with poor negative symptoms outcome ; ( b ) an opposite effect was observed for another sub-group of patients : patients with short DUP scored high on the negative symptoms scale and patients with long DUP reported only a few negative symptoms ; ( c ) there was no association between DUP and negative symptoms outcome for nearly half of the patients . These models were replicated in the Montreal sample . CONCLUSIONS The association between DUP and negative symptoms outcome might differ among sub-groups of first episode patients . Latent class regression analysis offers a flexible way to include unmeasured heterogeneity in outcome analyses Taxometric procedures such as mean above minus below a cut and maximum covariance can determine whether a trait is distributed as a discrete latent class . These methods have been used to infer taxonic structure in several personality and psychopathology constructs , often from analyses of rating scale data . This is problematic given ( a ) well established biases in ratings , ( b ) the human tendency to think categorically , and ( c ) implicit typological models of personality and psychopathology among expert raters . Using an experimental method in which the cognitive sets of raters were manipulated as dimensional versus categorical , it is demonstrated that pseudotaxonicity can be created readily with  rating scale measures . This suggests that research ers avoid an exclusive reliance on rating scales when conducting taxometrics investigations 
    Output:
    
Virtually all analyses yielded results that , on first impression , favored taxonic over dimensional interpretations of the latent structure of schizophrenia .
We conclude that there is no reason to seriously doubt a single-distribution model of schizophrenia because there is no evidence that provides a serious test of this null hypothesis .