Considerations for analysis of source monitoring data when investigating hallucinations in schizophrenia research

  • Todd S. WoodwardEmail author
  • Mahesh Menon
Original Paper


Self/other (i.e., internal/external) source monitoring is one of the leading paradigms for the study of hallucinations in schizophrenia. The cognitive processes that underlie hallucinations are theorized to transform self-generated (internal) cognitive events into other-generated (external) cognitive events. These proposed cognitive operations also appear to play a role in producing analogous types of errors in self/other source monitoring, namely a memory bias whereby recalled material that was self-generated is misremembered as other-generated, referred to as an externalization bias. Externalization biases are more frequent in groups of hallucinating schizophrenia patients than in other groups. One source of measurement error that is inherent in the study of the externalization bias is that, even for never-previously viewed items, there is a tendency to guess an external source under conditions of uncertainty. If such guessing takes place in response to self-generated but forgotten items, these guesses will be summed along with true externalization biases in the frequency count of externalizations, producing measurement error. Multinomial modeling is a statistical technique that has been used to estimate the influence of external-source guessing in order to separate it from true externalization bias estimates. However, a number of challenges related to model choice and model validation are involved, and these challenges may render multinomial modeling impractical. We instead recommend analysis of covariance (ANCOVA), or difference score methodology, as an appropriate method for partialling external-source guessing rates (external-source false positives) out of externalization bias rates.


Hallucinations Schizophrenia Source monitoring Multinomial modeling Analysis of covariance 



TSW is supported by a Scholar award from the Michael Smith Foundation for Health Research (MSFHR) and a New Investigator Award from the Canadian Institutes of Health Research (CIHR). Competing interests: the authors have no competing interests.


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Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  1. 1.Department of PsychiatryUniversity of British ColumbiaVancouverCanada
  2. 2.Department of ResearchBC Mental Health & Addictions Research InstituteVancouverCanada
  3. 3.Schizophrenia Program and PET CentreCentre for Addiction & Mental HealthTorontoCanada
  4. 4.Department of PsychiatryUniversity of TorontoTorontoCanada

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