Validity construct

A second objective is to produce behavioural changes in animals that are analogous to depression so that the model can be used to discover its neurobiological cause(s). This is a far more demanding problem and its success rests on satisfying at least three criteria (see Willner 1984) face validity (i.e. the behaviour looks like depression), construct validity (i.e. the causes and consequences of the behavioural change are the same as in depression) and predictive validity (i.e. the behaviour is reliably prevented only by drugs which have antidepressant effects in humans). 

There are three generally accepted criteria for validating animal models for human psychiatric disorders face validity, construct validity, and predictive validity. Face validity refers to the outward appearance of the model, i.e. does the animal s behavior adequately reflect the human behavior being modeled In this dimension, anxiety models have a clear advantage over other psychiatric models it is usually quite apparent if an animal is frightened, whereas it is a much more difficult to assess whether an animal is displaying psychotic-like or depressive-like behavior, for example. 

Instead, Cronbach and Meehl (1955) suggested that classification should be based on a construct validation approach. Construct validation involves developing a theory about a construct that is defined by a set of interconnected laws. These laws are ideas that relate constructs to one another as well as to observable behaviors. The set of constructs, laws, and observable behaviors is called a nomological network. 

Construct validation follows a three-stage process. The first stage, theory formulation, involves specifying relationships among constructs and their relation to external variables (e.g., etiological factors). Disorder x is created by process y. For example, a theory about the construct panic disorder could specify that it is caused by the catastrophic misinterpretation of benign bodily cues (Clark, 1986) or by a faulty suffocation monitor (Klein, 1993). Internal... 

Construct validation suggests that classification is central to and inseparable from theory. Classification of a disorder forms a representation of the theoretical construct that is needed for the basis of elaboration and testing of the theory. A classification system like the DSM provides a means of translating or operationalizing abstract theoretical ideas into more concrete (often behavioral) definitions. Testing the theory (classification system) rests on tests of its internal and external validity. These tests inform us about the adequacy of both the classification system and the theory. It is conceivabe that theory and classification evolve together over time. Theory creates an initial classification scheme that is evaluated and, when refined, informs us about theory. 

In many respects, the Waller et al. study is an exemplary taxometric report. The authors used multiple taxometric techniques and examined the construct validity of the taxon. However, three issues were not clarified in the report. First, only base rate estimates were reported and there was no discussion about shapes of the plots, so it is unclear how many of them were taxonic. Also, only one type of consistency test—cross-method consistency— was reported in the study although the different procedures were consistent with each other, it is difficult to determine the strength of each individual piece of evidence. Second, mini-scales were used for MAXSLOPE but not for the other analyses. The authors indicated that they created mini-scales because individual items are not very reliable. However, it is unclear why this would not also have been beneficial to the MAMBAC and MAXCOV analyses. Third, nuisance correlations and indicator validities were not computed. It is thus unclear how well the data conforms to CCK requirements, and how much we can trust the estimates. Moreover, this information could have been useful in assembling the DES-T. 

Let us examine how this interpretation fits with the biometric data. If the taxon simply reflects a transient reaction, it does not necessarily have to show strong associations with stable predispositions, such as inherited characteristics. However, it should covary with the presence of dissociation-provoking stressors, and adverse family environment is perhaps one of them. This account may or may not be able to explain the seeming inconsistency between the stability and biometric data. The issue needs to be explored in future studies, but it certainly highlights the importance of a thorough construct validation for newly discovered taxa. 

The results were not completely consistent, but these findings seem to favor a dimensional model of depression. However, this may reflect inadequate indicator selection. Taxometric power analysis suggests this is not the case, but the power analyses may have presented an overly optimistic view of indicator quality. In addition, the construct validity of the indicators used in this study is unknown. The validity of the BDI and the MMPI Scale 2 are well established, but the authors used indicators derived from these instruments, not the scales themselves. We cannot assume that the indicators assessed depression as accurately as the original scales. In fact, we don t know whether the derived scales are reliable. It is possible that the indicators actually did not tap syndromal depression, but instead they tapped a closely related factor such as negative affect, and thus are largely irrelevant to the question about the taxonicity of depression per se. 

The authors did not attempt to address this issue. Although construct validity is important, it does not guarantee taxometric validity, so both issues must be examined, especially in the case of null finding. For example, Franklin et al. could have performed a principal component analysis and examined loadings of the three indicators on the first unrotated component. As mentioned previously, these loadings can give a sense of indicator validity, and if the INTR failed to load sufficiently, this would indicate a measurement problem. 

Beach and Amir have demonstrated that with a given sample using the same procedures, some markers of depression may define a taxon, while others do not. In other words, both continuous and taxonic forms of depression exist. However, questions remain about the nature of the identified taxon. Is it really a depression taxon or has the exclusive focus on vegetative symptoms changed the nature of the construct Interestingly, certain somatic symptoms, such as sleep and appetite disturbance, are common in many disorders and can be considered the physical component of nonspecific distress (Clark Watson, 1991). Thus, perhaps the identified taxon is not a depression taxon at all and actually reflects general somatic complaints. Only construct validation can address these concerns. 

Construct Status Number of studies Strength of evidence Evidence of construct validity... 

Clark, L. A., Livesley, W. ]., Morey, L. (1997). Personality disorder assessment The challenge of construct validity. Journal of Personality Disorders, 11, 205-231. 

Clark, L. A., Watson, D. (1995). Constructing validity Basic issues in objective scale development. Psychological Assessment, 7, 309-319. 

Cronbach, L. J.,. Meehl, P. E. (1955). Construct validity in psychological tests. Psychological Bulletin, 52, 281-302. 

Frischholz, E. J., Braun, B. G., Sachs, R. G., Schwartz, D. R. (1991). Construct validity of the Dissociative Experiences Scale (DES) I. The relationship between the DES and other self-report measures of DES. Dissociation Progress in the Dissociative Disorders, 4, 185-188. 

Kotov, R., Schmidt, N. B., Lerew, D. R., Joiner, T. E., Ialongo, N. S. (2004). Latent structure of anxiety Taxometric exploration and construct validation. Manuscript submitted for publication. 

Lenzenweger, M. F., Bennett, M. E., Lilenfeld, L. R. (1997). The Referential Thinking Scale as a measure of schizotopy Scale development and initial construct validation. Psychological Assessment, 9, 452-463. 

Meehl, P. E. (1986). Diagnostic taxa as open concepts Meta-theoretical and statistical questions about reliability and construct validity in the grand strategy of nosological revision. In T. Millon G. L. Klerman (Eds.), Contemporary directions in psychopathology Toward the DSM-IV (pp. 215-231). New York Guilford. 

Watson, D. (2003). Investigating the construct validity of the dissociative taxon Stability analyses of normal and pathological dissociation. Journal of Abnormal Psychology, 112, 298-305. 

Yin (Yin, 1994) discusses four criteria forjudging the quality of the research design. After the external validity as already discussed, Yin defines the construct validity, the reliability, and the internal validity. The construct validity is the validity of the operational measures used for the research concepts. In this study construct validity will be addressed by the use of multiple sources for data collection. Case histories,... 

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