Instruments for Assessing Competency to Stand Trial: How Do They Work?

  • Nicholson R
  • Briggs S
  • Robertson H
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Previous research has demonstrated that the CST and a revised version of the GCCT-MSH accurately predict competency decisions made by forensic examiners. We used internal consistency analyses, item analyses, and factor analyses to determine how the instruments predict the competency criterion. Thesse analyses failed to reveal a clear basis for the predictive power of the CST. We were unable to establish correlates of the better predictors or to label the item clusters that emerged from the factor analyses. In contrast, analyses of the GCCT-MSH revealed a straightforward internal structure that comprised 3 factors. The factor that predicted staff decisions most accurately (Specific Legal Knowledge) constisted of items that were relevant for the individual defendant's case and that appeared to tap psychopathology as well as intelectual ability. This study highlights the need for investigators to examine the empirical relationships between psychological constructs and defendant's legally relevant functional abilities.Dusky standard: oriented and focused on the defendant's abilities as they relate to participation in the criminal trial process.Mental health professionals criticized presenting evidence: 1) irrelevant to the legal questions being asked; 2) unreliable or invalid: 3) incomprehensible to legal decision makers (#57)Purpose of article: How do these instruments predict competency to stand trial? and: criterion validity and construct validity. 1) internal consistency and homogeneity of intems; 2) predictive power of individual items; 3) information regarding internal structure of the tests.Method: N=140 defendants with court ordered pretrial examination of competency. 70% charged with at least one violent offense; 91.4% male; 63.6% black; mean age = 31.4; mean education = 9.7 years; 33.6% psychotic; 10.7% mentally retarded.CST and GCCT administered orally by clincal psychology residents, random order of adminstration within 4 weeks of of the den=fendants' admission to the unit. Compred to decision about competency made by a multidisciplinary staffing interview (6 weeks after admission = minimum 2 weeks after CST,GCCT) blind to CST and GCCT scores. 7.9% incompetent (unanimous); 86.4% competent (unanimous) 5.7% (divided but reclassified according to majority vote). Thus 89.9% competent and 11.1% incompetent.Results: 1) SCALE properties: scale reliability measured by alpha coefficient (CST = .85; GCCT; .88); scale homogeneity measured by mean interitem correlation (CST=.20; GCCT=.36). Correlations with staff decision (CST=.37 ; GCCT=.44)2) ITEM characteristics: interitem, intem-whole, item criterion correlations:no high interitem correlations (but higher for GCCT than CST); few high item-whole correlations but none significant (but higher for GCCT than CST); no high item-criterion correlations but a few were significant (but higher for GCCT than CST). few item psychosis correlations (but higher for GCCT than CST)3) FACTOR structure: principal axis factoring with a varimax rotation.6 factors for CST with eigenvalues over 1.0 but plateau after 3, kept 3. 3factors accounted for 28% of variance4 factors kept 3 factors for GCCT accounted for 49% of variance: 1)general legal knowledge; 2)courtroom layout; 3)legal proceedings (Specific legal knowledge). Meaning of these factors not clear4)FALSE and TRUE positives ??Discussion:1) significant or nearly significant correlations with years of education and diagnosis of mental retardation but not with psychosis Suggests that tests tap on intellectual abilities2) The internal structure of the CST is more complicated than the developers envisioned. CST possesses empirical utility but don't know why.3) GCCT-MSH: component of GCCT that predicted staff decisions most accurately was composed of items that were relevant to for the individual defendant and appeared to tap on psychopathology and intellectual abilityThe assessment process must include an inference as to the legitimacy of the functional impairment...Inherent in the construct of competency to stand trial are the issues of whether and apparent deficit can be controlled and whether it is likely to change (#60 chap.2)...Psychiatric and psychological conditions are relevant to the competency construct precisely because they influence the defndant's legally relevant functional abilities and might explain an observed deficit.Recommedn that examiners use the tests in order to obtain information about defendant's functional abilities, prefer GCCT-MSH to CST although predictive validity isn't much beter, it possesses a straightforward internal structure and lends itself more readily to description of defendants' legal abilitiesAppendix: CST and GCCT-MSH = copy

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  • Robert A. Nicholson

  • Stephen R. Briggs

  • Helen C. Robertson

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