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Open Access Publications from the University of California

Scholarly Works (6 results)

  • Article
  • Peer Reviewed
Postprints from TRC (2004)

Objective: Psychiatric clinical studies, including those in drug abuse research, often provide data that are challenging to analyze and use for hypothesis testing because they are heavily skewed and marked by an abundance of zero values. The authors consider methods of analyzing data with those characteristics. Method: The possible meaning of zero values and the statistical methods that are appropriate for analyzing data with many zero values in both cross-sectional and longitudinal designs are reviewed. The authors illustrate the application of these alternative methods using sample data collected with the Addiction Severity Index. Results: Data that include many zeros, if the zero value is considered the lowest value on a scale that measures severity, may be analyzed with several methods other than standard parametric tests. It zero values are considered an indication of a case without a problem, for which a measure of severity is not meaningful, analyses should include separate statistical models for the zero values and for the nonzero values. Tests linking the separate models are available. Conclusions: Standard methods, such as t tests and analyses of variance, may be poor choices for data that have unique features. The use of proper statistical methods leads to more meaningful study results and conclusions.

    Cover page: Methods for analysis of skewed data distributions in psychiatric clinical studies: Working with many zero values
    • Article
    • Peer Reviewed
    Postprints from TRC (2004)

    Understanding the long-term course of problematic drinking is a fundamental concern for health services research in the alcohol field. The stability of, or change in, the course of drinking-especially heavy drinking-has both theoretical and applied relevance to alcohol research. We explore the application of latent class growth modeling to 5 years of survey data collected from dependent and problem drinkers-some not in treatment at baseline-in an attempt to uncover prototypical longitudinal drinking patterns. Results indicated that five profiles of drinkers can be used to represent their longitudinal course of alcohol consumption: early quitters (N = 88), light/non-drinkers (N = 76), gradual improvers (N = 129), moderate drinkers (N = 229), and heavy drinkers (N = 572). Significant baseline factors included ASI drug severity, dependence symptoms, and marital status. Attendance at AA meetings, the size of one's heavy drinking and drug using social network, past treatment, receiving suggestions about one's drinking, and contacts with the medical system were significant influences. The size of heavy drinking and drug using social networks was noticeably larger for the heavy drinkers. Findings also support the usefulness of a semi-parametric latent group-based approach as a tool for analyzing alcohol-related behaviors. (C) 2004 Elsevier Ireland Ltd. All rights reserved.

      Cover page: Dependent and problem drinking over 5 years: a latent class growth analysis
      • Article
      • Peer Reviewed
      UC San Francisco Previously Published Works (2014)

      Background

      Until recently, hoarding was considered an obsessive-compulsive symptom (OCS). However, current evidence suggests that these two phenotypes may be clinically, and perhaps etiologically, distinct. Both hoarding and OCS have a genetic etiology, but the degree of unique and shared genetic contributions to these phenotypes has not been well studied.

      Method

      Prevalence rates were assessed for hoarding and OCS in a sample of adult twin pairs (n = 7906 twins) and their family members from The Netherlands Twin Register (total sample = 15,914). Using Mplus, genetic analyses using liability threshold models were conducted for both phenotypes, for their co-morbidity, and for specific hoarding symptoms (cluttering, discarding and acquiring).

      Results

      Of the total sample, 6.7% met criteria for clinically significant hoarding; endorsement of all three hoarding symptoms was > or = 79%. Men had slightly higher rates than women. Also, 5.7% met criteria for clinically significant OCS; rates were similar in males and females. Genetic factors accounted for 36% of the variance for hoarding and 40% of the variance for OCS. The genetic correlation between hoarding and OCS was 0.10. There was no evidence of sex-specific genetic contributions for hoarding or OCS. There was evidence for a genetic contribution to all hoarding symptom subtypes. Only cluttering showed evidence of a contribution from the shared environment.

      Conclusions

      OCS and hoarding are common in this population-based sample, have prevalence rates similar to those previously reported, and show significant heritability. Genetic factors contributed to the co-morbidity of both traits, although the genetic correlation between them was low.
        Cover page: Partitioning the etiology of hoarding and obsessive–compulsive symptoms
        • Article
        • Peer Reviewed
        UC San Francisco Previously Published Works (2015)
          Cover page: Latent class models identify two subphenotypes in respiratory distress syndrome with differential response to positive end-expiratory pressure.
          • Article
          • Peer Reviewed
          UC San Francisco Previously Published Works (2014)
          Background: Subphenotypes have been identified within heterogeneous diseases such as asthma and breast cancer, with important therapeutic implications. We assessed whether subphenotypes exist within acute respiratory distress syndrome (ARDS), another heterogeneous disorder. Methods: We used data from two ARDS randomised controlled trials (ARMA trial and ALVEOLI trial), sponsored by the National Heart, Lung, and Blood Institute. We applied latent class modelling to identify subphenotypes using clinical and biological data. We modelled data from both studies independently. We then tested the association of subphenotypes with clinical outcomes in both cohorts and with the response to positive end-expiratory pressure (PEEP) in the ALVEOLI cohort. Findings: We analysed data for 1022 patients: 473 in the ARMA cohort and 549 in the ALVEOLI cohort. Independent latent class models indicated that a two-class (ie, two subphenotype) model was the best fit for both cohorts. In both cohorts, we identified a hyperinflammatory subphenotype (phenotype 2) that was characterised by higher plasma concentrations of inflammatory biomarkers, a higher prevalence of vasopressor use, lower serum bicarbonate concentrations, and a higher prevalence of sepsis than phenotype 1. Participants in phenotype 2 had higher mortality and fewer ventilator-free days and organ failure-free days in both cohorts than did those in phenotype 1 (p<·007 for all). In the ALVEOLI cohort, the effects of ventilation strategy (high PEEP vs low PEEP) on mortality, ventilator-free days and organ failure-free days differed by phenotype (p=·049 for mortality, p=·018 for ventilator-free days, p=·003 for organ-failure-free days). Interpretation: We have identified two subphenotypes within ARDS, one of which is categorised by more severe inflammation, shock, and metabolic acidosis and by worse clinical outcomes. Response to treatment in a randomised trial of PEEP strategies differed on the basis of subphenotype. Identification of ARDS subphenotypes might be useful in selecting patients for future clinical trials. Funding: National Institutes of Health. © 2014 Elsevier Ltd.
            Cover page: Subphenotypes in acute respiratory distress syndrome: Latent class analysis of data from two randomised controlled trials
            • Article
            • Peer Reviewed
            UC San Francisco Previously Published Works (2017)

            Background

            Genetic-epidemiological studies that estimate the contributions of genetic factors to variation in tic symptoms are scarce. We estimated the extent to which genetic and environmental influences contribute to tics, employing various phenotypic definitions ranging between mild and severe symptomatology, in a large population-based adult twin-family sample.

            Method

            In an extended twin-family design, we analysed lifetime tic data reported by adult mono- and dizygotic twins (n = 8323) and their family members (n = 7164; parents and siblings) from 7311 families in the Netherlands Twin Register. We measured tics by the abbreviated version of the Schedule for Tourette and Other Behavioral Syndromes. Heritability was estimated by genetic structural equation modeling for four tic disorder definitions: three dichotomous and one trichotomous phenotype, characterized by increasingly strictly defined criteria.

            Results

            Prevalence rates of the different tic disorders in our sample varied between 0.3 and 4.5% depending on tic disorder definition. Tic frequencies decreased with increasing age. Heritability estimates varied between 0.25 and 0.37, depending on phenotypic definitions. None of the phenotypes showed evidence of assortative mating, effects of shared environment or non-additive genetic effects.

            Conclusions

            Heritabilities of mild and severe tic phenotypes were estimated to be moderate. Overlapping confidence intervals of the heritability estimates suggest overlapping genetic liabilities between the various tic phenotypes. The most lenient phenotype (defined only by tic characteristics, excluding criteria B, C and D of DSM-IV) rendered sufficiently reliable heritability estimates. These findings have implications in phenotypic definitions for future genetic studies.
              Cover page: Heritability of tic disorders: a twin-family study.
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