Precursors for schizophrenia : are schizotaxia and schizotypy related?
Whitehead, Kirsty Victoria
Meehl's (1962, 1989, 1990b) schizotypy and Tsuang et al.'s (1999b, 2000a, 2000b) schizotaxia are fundamentally different notions of the schizophrenia precursor. Both represent a categorical precursor but differ in the nature of their relationships to schizophrenia. Specifically, schizotypy is dimensional, unchanging despite the presence or remission of schizophrenia In contrast, schizotaxia is a transitional precursor; the presence of schizophrenia signals the end of schizotaxia. There are also differences in the way in which risk is determined. Schizotypy is reflected in a variety of information processing and experiential aberrations, is typically assessed using self-report measures, and is best identified using taxometric analyses. In contrast, schizotaxia is characterised by negative symptoms of schizophrenia and neurocognitive impairment, can be assessed using standardised clinical measures, and is diagnosed at the individual case level. The aim of Phase 1 of this study was to investigate the manifest structure of Meehl’s schizotypy in a sample of psychiatric patients. The aims of Phase 2 were to determine if schizotypy group membership was associated with poorer functioning and to determine the nature of the relationship between Meehl's (1962, 1989, 1990b) schizotypy and Tsuang et al.'s (1999b, 2000a, 2000b) schizotaxia. Participants in Phase 1 were 109 psychiatric patients and all completed a self-report measure of schizotypy, the Thinking and Perceptual Style Questionnaire (TPSQ; Linscott & Knight, 2004). Multivariate taxometric analyses of TPSQ subscales yielded evidence of a manifest group structure within the sample. The prevalence of the latent group, presumed to reflect schizotypy, was estimated to be 32% (SD= 8%) as yielded by MAXCOV analyses. MAXCOV analyses also yielded a mean indicator validity of 1.02; variance of 7; base rate estimates of .08; and a goodness of fit index of .98. MAMBAC analyses yielded a mean base rate of 56% (SD = 18%). Twenty-nine participants from Phase 1 took part in Phase 2. Fourteen were from the schizotypy group (had a p value of .85 or higher of schizotypy group membership) and 15 from the nonschizotypy group (had a p value of .03 or lower of schizotypy group membership). Participants completed tests of attention, verbal memory, and executive functioning. Negative symptoms of schizophrenia were also rated and diagnosis was determined using a diagnostic interview. The schizotypy group was significantly impaired relative to the nonschizotypy group on neuropsychological test scores spanning domains of attention, verbal memory, and executive functioning. A current DSM-IV diagnosis was made for 71 % of the schizotypy group and 43% of the nonschizotypy group. Individuals were classified as having met criteria for schizotaxia if they had a negative symptom impairment and a neuropsychological impairment in two domains. A total of 7 people of 29 met criteria for schizotaxia, 6 of these people were from the schizotypy group. There was statistical evidence that Meehl's (1962, 1989, 1990b) schizotypy and Tsuang et al.'s (1999b, 2000a, 2000b) schizotaxia are not independent. The proposed precursors for schizophrenia may reflect the same construct, not separate entities. Limitations and implications of these results are considered.
Advisor: Linscott, Richard
Degree Name: Doctor of Philosophy
Degree Discipline: Psychology
Publisher: University of Otago
Research Type: Thesis