Biomedical subjects

X M Tu

Publications and source records attributed to X M Tu.

16 recordsLinked to original sources

PubMed1999

Bayesian analysis of prevalence with covariates using simulation-based techniques: applications to HIV screening.

Ignoring the limited precision of medical diagnostic tests can incur serious bias in prevalence estimation. Conversely, treating the values of sensitivity and specificity as constants, as in most studies, inevitably underestimates the variability of prevalence estimates. Bayesian inference provides a natural framework with which to integrate the variability in the estimates of sensitivity and specificity with estimation of prevalence. However, the resulting model becomes quite complicated and presents a computational challenge. Recently, Mendoza-Blanco et al. proposed a missing-data approach with simulation-based techniques to deal with the computational difficulties. Although their approach is quite effective in reducing the computational complexity into manageable tasks, their developed methodology is not general enough for modelling the effects of covariates in prevalence estimation. In this paper, we extend their work in this direction by combining their missing-data approach with a latent variable technique for modelling discrete data. The present work also generalizes the methods of Albert and Chib for Bayesian analysis of binary response data with errors in the response. We illustrate the methodology with several real data examples extracted from the literature.

AIDS Serodiagnosis↗

PubMed1999

Pretreatment REM sleep and subjective sleep quality distinguish depressed psychotherapy remitters and nonremitters.

BACKGROUND: We compared pretreatment subjective and electroencephalographic sleep measures among depressed patients who remitted with psychotherapy alone and those who did not remit. METHODS: Patients were 111 midlife women with recurrent major depressive disorder. Baseline psychiatric ratings and sleep studies were conducted prior to treatment with weekly interpersonal psychotherapy. Remission was defined as a score of < or = 7 for 3 consecutive weeks on the Hamilton Depression Rating Scale. Clinical and sleep measures were compared between remitters (n = 62) and nonremitters (n = 49) using t tests and random regression. Linear discriminant function analyses were used to categorize remitters and nonremitters on the basis of sleep measures. RESULTS: Treatment nonremitters had significantly worse subjective sleep quality and significantly elevated phasic REM sleep as measured by multivariate and univariate analyses. The linear accumulation of REM activity during sleep occurred at a significantly higher rate in nonremitters than in remitters. Linear discriminant function analyses based on subjective sleep quality and REM activity correctly identified 68.3% of nonremitters and 68.5% of remitters. CONCLUSIONS: These findings highlight the role of subjective and REM sleep measures as correlates of short-term psychotherapy treatment response in major depressive disorder. Disturbed sleep may be a physiological indicator of increased limbic and brain stem arousal.

Adult↗

PubMed1998

Latent structure of EEG sleep variables in depressed and control subjects: descriptions and clinical correlates.

In this study, we aimed to determine the latent structure of multiple EEG sleep variables in patients with major depressive disorder (MDD) and in healthy control subjects and to examine associations between sleep factors and clinical variables. Subjects included 109 women with MDD and 54 healthy control women. EEG sleep data were collected prior to any treatment. Principal components analysis (PCA) was conducted on a set of 24 sleep variables. Separate PCAs were run for patients with MDD, control subjects, and a matched group of patients and controls. Other analyses included correlations, t-tests and MANOVA. Each PCA identified four sleep factors that explained 70% of the total variance in individual sleep variables: slow wave sleep, REM sleep, sleep continuity and REM latency/delta sleep ratio (RL/DSR). Patients with MDD and healthy controls differed on the mean value of the sleep continuity factor, and a multivariate analysis of variance based on the PCA identified MDD-control differences in REM sleep and sleep continuity. In the MDD group, slow wave sleep correlated inversely with age and personality disorder symptoms; sleep continuity correlated with subjective sleep quality and anxiety; and RL/DSR correlated inversely with age. The mean value of the REM factor was higher among treatment non-responders than responders. EEG sleep variables have a similar latent structure in women with MDD and in healthy controls. These sleep factors are supported conceptually and empirically, and correlate with clinical measures in women with MDD. Multivariate statistical techniques decrease the risk of Type I and Type II errors when using a large number of collinear sleep measures, and can clarify conceptual issues related to sleep and depression.

Adult↗

PubMed1997

Inducing lifestyle regularity in recovering bipolar disorder patients: results from the maintenance therapies in bipolar disorder protocol.

On the basis of theories we articulated in earlier papers (Ehlers et al 1988: Arch Gen Psychiatry 45:948-952, 1993: Depression 1:285-293), we have developed an adjunctive psychosocial intervention for patients with bipolar 1 disorder. Central to this intervention is the establishment of regularity in daily routines. In this report, we present data from a controlled investigation comparing this new treatment, interpersonal and social rhythm therapy (IPSRT), with a conventional medication clinic approach. Despite comparable changes in symptomatology over a treatment period lasting up to 52 weeks, subjects assigned to IPSRT (n = 18) show significantly greater stability (p = .047) of daily routines with increasing time in treatment, while subjects assigned to the medication clinic condition (n = 20) show essentially no change in their social routines as measured by Social Rhythm Metric (SRM-Monk et al 1990: J Nerv Ment Dis 178(2):120-126) score. We conclude that IPSRT is capable of influencing lifestyle regularity in patients with bipolar 1 disorder, with the possible benefit of protection against future affective episodes.

Adult↗

PubMed1997

A prospective test of criteria for response, remission, relapse, recovery, and recurrence in depressed patients treated with cognitive behavior therapy.

The definitions that are commonly employed to describe the outcome of the depressive disorders are often used in inconsistent ways and remain largely untested. The lack of a standard and valid set of outcome definitions hinders the study of the naturalistic course and treatment of depressive disorders. In the present study, we operationalized definitions for response, remission, relapse, recovery, and recurrence and examined their validity in a sample of depressed patients treated with cognitive behavior therapy. Validity was evaluated by the ability of the definitions to predict subsequent outcome in acute treatment and during a 3 year follow-up period. All five definitions demonstrated moderate to excellent validity. Moreover, we were able to empirically distinguish response from remission, and relapse from recurrence, despite the frequent confusion of these terms in the literature. Several of the findings suggest that continued refinement of the outcome definitions may enhance validity even further.

Adult↗

PubMed1997

Mortality of elderly patients with psychiatric disorders.

OBJECTIVE: The goal of this study was to evaluate the impact of common late-life mental disorders on the life expectancy and causes of death of older psychiatric patients. METHOD: The study population consisted of 809 older psychiatric patients who met DSM-III-R criteria for organic mental disorders, mood disorders, or psychotic disorders and who were discharged after a comprehensive multidisciplinary evaluation and acute inpatient treatment for their behavioral disorders. Dates and causes of death during a 5.75-year follow-up period were provided by the Pennsylvania Department of Health. Univariate and multivariate survival procedures were used to compare the survival rates of the three groups to each other and to a reference population of Pennsylvania residents. Causes of death were also tabulated according to ICD-9-CM and compared across the groups. RESULTS: Age, gender, race, and medical comorbidity made significant independent contributions to survival. When these variables were controlled, the survival of patients with organic mental disorders was less than half of that for patients with mood or psychotic disorders. However, all three groups experienced higher rates of mortality than the reference population, with standardized mortality ratios of 1.5 to 2.5. Deaths occurred from the usual spectrum of natural causes, with the exception that patients with mood disorders were more likely to have died from disorders of the digestive system and suicide. CONCLUSIONS: The mental disorders of late life have a significant negative impact on the survival of older psychiatric patients.

Age Factors↗

PubMed1997

Generalized covariance-adjusted discriminants: perspective and application.

When discriminant analysis is used in practice for assessing the usefulness of diagnostic markers, the lack of control over covariates motivates the need for their adjustment in the analysis. This necessity for adjustment arises especially when the researcher's aim is classification based on a set of diagnostic markers and is not based on a set of covariates for which there exists known heterogeneity among the subjects with respect to the groups under consideration. The traditional covariance-adjusted approach is restrictive for such applications in that they assume linear covariates and a normal distribution for the the feature vector. Further, there is no available method for variable selection in using such covariance-adjusted models. In this paper, we generalize the traditional covariance-adjusted model to a general normal and logistic model, where these generalized models not only relax the distributional assumptions on the feature vector but also allow for nonlinear covariates. Exact and asymptotic tests are also derived for the problem of variable selection for these new models. The methodology is illustrated with both simulated data and an actual data set from a psychiatric study on using the Social Rhythm Metric for patients with anxiety disorders.

Activities of Daily Living↗

PubMed1997

Is life stress more likely to provoke depressive episodes in women than in men?

One of the most consistent findings in psychiatric research is that rates of major depression are at least twofold higher among women than among men. Although there is considerable agreement in the literature that life events play a role in producing, triggering, or maintaining episodes of depression, less is known about the relationship among gender, life events, and depression. In the present study, we compared the rates, focus ("interpersonal" vs. "non-interpersonal"), and timing of stressful life experiences reported in rigorous interviews of male and female patients with unipolar recurrent depression and nondepressed contrast subjects. Consistent with hypotheses, female patients were more likely to experience stressful life experiences than their male counterparts; rates of stressful life experiences did not differ between female and male controls. Unexpectedly, rates of interpersonal stress did not differ among males and females regardless of patient or control status. We also found no significant differences in the timing of pre-onset events: stressful events were generally concentrated in the period immediately preceding onset for both men and women. Thus, although these data suggest that life stress may play a larger role in the provocation of recurrent episodes of depression for women than for men, there do not seem to be sex differences in the extent to which interpersonal vs. noninterpersonal events and difficulties are associated with depression onset or in the temporal distribution of events. Implications of these results are discussed in the context of research on other putative factors contributing to gender differences in rates of depression.

Adult↗

PubMed1996

Bayesian inference on prevalence using a missing-data approach with simulation-based techniques: applications to HIV screening.

Health departments and other health-related authorities seek accurate assessment of the spread of human immunodeficiency virus (HIV) among populations. Although screening for HIV provides a direct means for estimating its prevalence, it is complicated by the heterogeneity of available diagnostic tests and the degree to which they can diagnose HIV accurately. To integrate the limited precision of screening tests with prior results, Bayesian inference becomes a method of choice. Current Bayesian methods, however, have limited applications and do not readily generalize for complicated sampling designs and for modelling needs, particularly those that relate to HIV screening. By utilizing recent developments in the theories of missing-data analysis and simulation-based techniques, we develop an approach to Bayesian analysis of prevalence. This methodology is quite general for a variety of sampling schemes and sufficiently flexible to accommodate various practical considerations that arise from HIV screening. We illustrate the methodology with real as well as simulated data sets. Further, by utilizing the methodology, we performed simulations to demonstrate that pooled testing provides a cost-effective means to improve the precision of estimates of prevalence under the currently limited screening technology.

Algorithms↗

PubMed1996

Effects of positive and negative life events on time to depression onset: an analysis of additivity and timing.

While the relationship of life events to depression onset has occupied researchers for almost a quarter of a century, few studies have attempted to account for either the temporal patterning of events relative to episode onset, or, the effect of multiple events in a study period. In this report, we attempt to address the issues of timing of events, multiple events (both positive and negative) and multiple aspects (both positivity and negativity) of single events on latency time to depression onset, while simultaneously accounting for possible decay in the effects of events over time. We use the proportional hazards approach to model the effects of life events and consider modelling the change in impact of events with the passage of time. After interviewing 142 recurrent unipolar patients using the Life Events and Difficulties Schedule, we rated severity and positivity of life events reported during the 6-month period prior to onset. As we hypothesized, additional life events occurring after an initial provoking agent level event significantly alter the risk of illness onset. Additional severely threatening events decrease the time to onset, but positive events do not appear to delay onset. Interestingly, seemingly neutral events had a highly significant effect in shortening the time to onset. We note the many limitations imposed on the interpretation of these findings related to the selected group of subjects studied and encourage those who have more generalizable data to apply these methods of analysis.

Adult↗

PubMed1994

Impact of acute psychiatric inpatient treatment on major depression in late life and prediction of response.

OBJECTIVE: The authors conducted a prospective study to examine the sociodemographic and clinical characteristics of elderly inpatients with major depression and their response to acute psychiatric hospitalization. The relation between the descriptive variables and clinical response was also investigated. METHOD: The subjects were 205 consecutively admitted inpatients, whose mean age was 71 years, who met the DSM-III-R criteria for major depression. Each subject received detailed physical, psychiatric, and mental status examinations, along with quantitative assessments of psychiatric symptoms and cognitive performance at admission and at discharge. Management of physical problems was optimized, and patients were treated with a combination of somatic and psychotherapeutic interventions. The average duration of hospitalization was approximately 1 month. RESULTS: Despite considerable medical and psychiatric comorbidity, the patients responded well to treatment, as reflected by a 50% reduction in the average score on the Hamilton Depression Rating Scale. Nearly one-half of the patients had experienced the resolution of their depressive symptoms by the time of discharge. Race, cognitive performance at admission, number of medical problems, use of ECT, and length of hospitalization independently contributed to the prediction of clinical response. Response to treatment was not related to the other sociodemographic variables examined or to any of the indexes of severity of depressive episode. CONCLUSIONS: Short-term psychiatric hospitalization offers an effective and efficient vehicle for the treatment of severe or complicated cases of major depression in the elderly, even when considerable medical and psychiatric comorbidity is present.

Age Factors↗

PubMed1994

Modelling progression of CD4-lymphocyte count and its relationship to survival time.

The purpose of this article is to model the progression of CD4-lymphocyte count and the relationship between different features of this progression and survival time. The complicating factors in this analysis are that the CD4-lymphocyte count is observed only at certain fixed times and with a high degree of measurement error, and that the length of the vector of observations is determined, in part, by the length of survival. If probability of death depends on the true, unobserved CD4-lymphocyte count, then the survival process must be modelled. Wu and Carroll (1988, Biometrics 44, 175-188) proposed a random effects model for two-sample longitudinal data in the presence of informative censoring, in which the individual effects included only slopes and intercepts. We propose methods for fitting a broad class of models of this type, in which both the repeated CD4-lymphocyte counts and the survival time are modelled using random effects. These methods permit us to estimate parameters describing the progression of CD4-lymphocyte count as well as the effect of differences in the CD4 trajectory on survival. We apply these methods to results of AIDS clinical trials.

Acquired Immunodeficiency Syndrome↗

PubMed1994

Regression analysis of censored and truncated data: estimating reporting-delay distributions and AIDS incidence from surveillance data.

AIDS surveillance provides a vital source of information for health departments to assess the AIDS epidemic and to plan for future health-care needs. However, the use of surveillance data requires proper adjustments for the underreporting of AIDS cases caused by the delay in reporting diagnosed AIDS cases to the surveillance system. The statistical problem of adjusting for this underreporting concerns making inferences about an unobservable random sample of which only a portion is observed in a chronologic time interval defined by the analysis. Most regression methods for making inferences using right-truncated data employ a reverse-time hazard function, which requires that the observed data be transformed so that methods for left-truncated data can be applied. In this paper, we discuss fitting regression models to data that can be truncated and even censored in arbitrary intervals. The proposed methodology was applied to the national AIDS surveillance data provided by the Centers for Disease Control to analyze the trend of delays over chronologic time and variation among different geographic regions as well as across risk groups.

Acquired Immunodeficiency Syndrome↗

PubMed1993

Survival differences and trends in patients with AIDS in the United States.

The AIDS surveillance system maintained by the Centers for Disease Control and Prevention (CDC) provides a unique data base for estimating survival after a diagnosis of AIDS for the general AIDS population in the United States. Because patients enrolled in most AIDS clinical trial studies receive unusual medical care that may not be available to the general public and typically have relatively longer survival time, estimates obtained from these studies may not be of direct use in assessing the national health-care needs. Furthermore, such studies are usually of short duration and may not be very informative for long-term health-policy planning. We present survival estimates obtained from the CDC surveillance data for the adult/adolescent AIDS population in the United States and compare their survival and trend in survival on gender, sexual behavior, and injection-drug use status. These estimates provide information for mortality risk after an AIDS diagnosis over a period of 8 years and for trend of survival during the period between 1983 and 1991.

Acquired Immunodeficiency Syndrome↗

PubMed1992

Issues in human immunodeficiency virus (HIV) screening programs.

Unlike test sensitivity and specificity, the false positive and negative predictive values (probabilities of mislabeling an individual being tested) depend heavily on the prevalence of the infection of the human immunodeficiency virus (HIV) as well as the quality of the kit. A consequence of this dependence is that the false positive predictive value can reach a high magnitude such as 0.9; that is, 90% of the positive tests are false. This raises many important issues pertaining to the current practice of HIV screening such as to how to control these misclassification errors, how to interpret test results, and how to estimate prevalence using test results. These issues are examined in detail here by considering the factors that dictate the quality of a screening program. Some real data examples are used to illustrate the importance of this consideration in designing programs to achieve the desired goals. The rationale behind the common two-step sequential protocol in HIV screening is examined to point out its limitations under practical situations. Finally, the use of entropy in evaluating the informativeness of a screening program is discussed.

AIDS Serodiagnosis↗

PubMedDate not supplied

Studies of AIDS and HIV surveillance. Screening tests: can we get more by doing less?

Estimating the prevalence of the human immunodeficiency virus (HIV) in a group is challenging; this is especially so when the prevalence is small. One reason is that the presence of measurement errors resulting from the limited precision of tests makes estimation, using traditional methods, impossible in some screening situations. Measurement error is real, ignoring it leads to severe bias, and inference about the prevalence becomes unsatisfactory. Indeed, in a low prevalence situation the expected number of false positives is very high, often even higher than the number of true positives. The second reason is that in the low prevalence areas the large sample is needed in order to obtain non-zero estimate. This is usually a very costly, and often unrealistic, solution. This paper considers the advantages and disadvantages of pooled testing as an alternative solution to this problem. We show that by pooling sera samples we not only achieve a cost saving but also, which is counterintuitive, an increase in the estimation accuracy. We also discuss the statistical issues associated with the resulting estimator.

Acquired Immunodeficiency Syndrome↗