The Lifetime Dimensions of Psychosis Scale (LDPS): Description and Interrater Reliability
by Douglas F. Levinson, Bryan J. HAowry, Michael A. Escamilla, and Stephen V. Faraone
A new rating scale, the Lifetime Dimensions of Psychosis Scale (LDPS), is described. The LDPS cre- ates a profile of the lifetime characteristics of each case based on retrospective ratings, encompassing the posi- tive, bizarre, negative, and disorganized symptom fac- tors identified by previous studies of psychotic disor- ders, plus mood-related symptomatology, degree of deterioration, and complicating factors over the course of illness. A preliminary 39-item scale and instruction manual were developed. Intraclass correlation coeffi- cients (ICCs) for positive symptom and mood item total scores were 0.76 to 0.87 (mean of 0.70 for all items). Highly intercorrelated (tau-b coefficients) or unreliable items were eliminated to create the final 20- item version 2. Good-excellent reliability was observed in a second study using different raters. The LDPS is designed for use by experienced clinicians or researchers who have access to comprehensive clinical information, including semistructured diagnostic interviews, psychiatric records, and family history reports. Dimensional scores and multidimensional pat- terns might prove useful in studying the relationship of clinical phenotype to genotypes, treatment response, and other variables. They may also be useful in clinical practice.
Keywords: Psychosis, schizophrenia, dimensions, rating scale, reliability. Schizophrenia Bulletin, 28(4):683-695, 2002.
We report here on the development of the preliminary and revised versions of a new dimensional rating scale for sub- jects with psychotic disorders, the Lifetime Dimensions of Psychosis Scale (LDPS). Described here are the initial selection of items, a study of their interrater reliability, a preliminary analysis of factor structure and intercorrela- tion among items, the creation of a shorter revised version based on elimination of highly intercorrelated and unreli-
able items, and an interrater reliability study of the revised scale. While further studies are needed to determine its validity and applicability, the LDPS or similar scales might prove useful for studying a range of symptom dimensions over the course of illness, the dimensions' relationships to each other, and the clustering of clinical profiles across the broad range of psychotic cases observed in the population, rather than assigning these cases to existing categories.
We developed the LDPS as an initial attempt to address the shortcomings of categorical diagnostic sys- tems, based on experience in evaluating psychotic subjects for genetic studies of schizophrenia and mood disorders, as well as clinical practice. Categorical systems do not characterize the pattern of clinical features over the entire course of illness, the substantial differences in clinical fea- tures of subjects with the same categorical diagnosis, or the full range of features that differentiate individuals across the spectrum of psychotic disorders. Different diag- noses can be assigned to subjects who differ only slightly in symptoms and course, while the same diagnosis can be assigned to subjects who bear little resemblance.
This is particularly true for cases with mixtures of mood and psychotic symptoms. For a subject with chronic positive, negative, and disorganized symptoms, the DSM-IV diagnosis is schizophrenia if mood syndromes are "not prominent," or schizoaffective disorder if they are "prominent" (albeit very slightly more so than in the first case). A schizoaffective diagnosis is also given for certain remitting syndromes where psychosis persists for a few weeks after mood episodes. Not surprisingly, the interrater reliability of schizoaffective diagnoses is often poor even in the hands of research clinicians (Nurnberger et al. 1994; Faraone et al. 1996; Roy et al. 1997). Yet, mixed symp-
Send reprint requests to Dr. D.F. Levinson, Department of Psychiatry, U n i v e r s i t y o f P e n n s y l v a n i a S c h o o l o f M e d i c i n e , R o o m 4 0 0 6 , 3 5 3 19104-3309; 5 e-mail: Market Philadelphia, Street, PA