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Thomas A Louis

Publications and source records attributed to Thomas A Louis.

At least 19 recordsLinked to original sources
PubMed2006

Training of the next generation of biostatisticians: a call to action in the U.S.

Two workshops (2001, 2003) were held by the National Institutes of Health (NIH) to examine the need to train more biostatisticians in the U.S. to meet the increasing opportunities in the biomedical research enterprise. The supply of new PhD graduates in biostatistics in the U.S. has been relatively steady for the past two decades while the demand has increased dramatically. These workshops concluded that a renewed effort must be made in the U.S., led in part by the NIH, to add to and expand the existing training programs to increase the supply. This article summarizes those two workshops and their recommendations. Some progress has been made through a new biostatistics training program with emphasis in bioinformatics sponsored by the National Institute of General Medical Sciences (NIGMS).

Biological Science Disciplines↗
PubMed2006

Consumer decision making in the individual health insurance market.

This paper summarizes the results from a study of consumer decision making in California's individual health insurance market. We conclude that price subsidies will have only modest effects on participation and that efforts to reduce nonprice barriers might be just as effective. We also find that there is substantial pooling in the individual market and that it increases over time because people who become sick can continue coverage without new underwriting. Finally, we show that people prefer more-generous benefits and that it is difficult to induce people in poor health to enroll in high-deductible health plans.

California↗
PubMed2006

Analysis of repeated pregnancy outcomes.

Women tend to repeat reproductive outcomes, with past history of an adverse outcome being associated with an approximate two-fold increase in subsequent risk. These observations support the need for statistical designs and analyses that address this clustering. Failure to do so may mask effects, result in inaccurate variance estimators, produce biased or inefficient estimates of exposure effects. We review and evaluate basic analytic approaches for analysing reproductive outcomes, including ignoring reproductive history, treating it as a covariate or avoiding the clustering problem by analysing only one pregnancy per woman, and contrast these to more modern approaches such as generalized estimating equations with robust standard errors and mixed models with various correlation structures. We illustrate the issues by analysing a sample from the Collaborative Perinatal Project dataset, demonstrating how the statistical model impacts summary statistics and inferences when assessing etiologic determinants of birth weight.

Adolescent↗
PubMed2006

Feasibility of retinoids for the treatment of emphysema study.

BACKGROUND: Retinoids promote alveolar septation in the developing lung and stimulate alveolar repair in some animal models of emphysema. METHODS: One hundred forty-eight subjects with moderate-to-severe COPD and a primary component of emphysema, defined by diffusing capacity of the lung for carbon monoxide (Dlco) [37.1 +/- 12.0% of predicted] and CT density mask (38.5 +/- 12.8% of voxels <- 910 Hounsfield units) [mean +/- SD] were enrolled into a randomized, double-blind, feasibility study at five university hospitals. Participants received all-trans retinoic acid (ATRA) at either a low dose (LD) [1 mg/kg/d] or high dose (HD) [2 mg/kg/d], 13-cis retinoic acid (13-cRA) [1 mg/kg/d], or placebo for 6 months followed by a 3-month crossover period. RESULTS: No treatment was associated with an overall improvement in pulmonary function, CT density mask score, or health-related quality of life (QOL) at the end of 6 months. However, time-dependent changes in Dlco (initial decrease with delayed recovery) and St. George Respiratory Questionnaire (delayed improvement) were observed in the HD-ATRA cohort and correlated with plasma drug levels. In addition, 5 of 25 participants in the HD-ATRA group had delayed improvements in their CT scores that also related to ATRA levels. Retinoid-related side effects were common but generally mild. CONCLUSIONS: No definitive clinical benefits related to the administration of retinoids were observed in this feasibility study. However, time- and dose-dependent changes in Dlco, CT density mask score, and health-related QOL were observed in subjects treated with ATRA, suggesting the possibility of exposure-related biological activity that warrants further investigation.

Aged↗
PubMed2005

Projecting the number of patients with end-stage renal disease in the United States to the year 2015.

The size of the prevalent ESRD population in the United States increased dramatically during the 1990s, from 196,000 in 1991 to 382,000 in 2000. Incidence also increased considerably during the same period, from 53,000 to 93,000 per year. If previous trends in ESRD incidence and prevalence continue, then current levels of health care resources that are devoted to the care of these patients will eventually be unable to meet the demand. This study discusses a Markov model developed to predict ESRD incidence, prevalence, and mortality to the year 2015 and incorporating expected changes in age/race distributions, diabetes prevalence, ESRD incidence, and probability of death. The model predicted that by 2015 there will be 136,166 incident ESRD patients per year (lower/upper limits 110,989 to 164,550), 712,290 prevalent patients (595,046 to 842,761), and 107,760 ESRD deaths annually (96,068 to 118,220). Incidence and prevalence counts are expected to increase by 44 and 85%, respectively, from 2000 to 2015 and incidence and prevalence rates per million population by 32 and 70%, respectively. The financial and human resources that will be needed to care for these patients in 2015 will be considerably greater than in 2005.

Age Distribution↗
PubMed2005

Assessing the implementation of the chronic care model in quality improvement collaboratives.

OBJECTIVE: To measure organizations' implementation of Chronic Care Model (CCM) interventions for chronic care quality improvement (QI). DATA SOURCES/STUDY SETTING: Monthly reports submitted by 42 organizations participating in three QI collaboratives to improve care for congestive heart failure, diabetes, depression, and asthma, and telephone interviews with key informants in the organizations. STUDY DESIGN: We qualitatively analyzed the implementation activities of intervention organizations as part of a larger effectiveness evaluation of yearlong collaboratives. Key study variables included measures of implementation intensity (quantity and depth of implementation activities) as well as fidelity to the CCM. DATA COLLECTION/EXTRACTION METHODS: We developed a CCM-based scheme to code sites' intervention activities and criteria to rate their depth or likelihood of impact. PRINCIPAL FINDINGS: The sites averaged more than 30 different change efforts each to implement the CCM. The depth ratings for these changes, however, were more modest, ranging from 17 percent to 76 percent of the highest rating possible. The participating organizations significantly differed in the intensity of their implementation efforts (p<.001 in both quantity and depth ratings). Fidelity to the CCM was high. CONCLUSIONS: Collaborative participants were able, with some important variation, to implement large numbers of diverse QI change strategies, with high CCM fidelity and modest depth of implementation. QI collaboratives are a useful method to foster change in real world settings.

Chronic Disease↗
PubMed2005

Introduction to Bayesian methods II: fundamental concepts.

The use of Bayesian design and analysis is burgeoning. In this introduction to Bayesian methods, we provide basic examples of Bayesian thinking and formalism on which more complicated and comprehensive approaches are built. These include adjusting estimates using related information, the use of Bayes theorem in diagnostic testing, the relationship of the prior and posterior distributions for situations where both the data and prior distribution are Gaussian, and the key steps in a Bayesian analysis. If Bayesian methods are carefully developed and applied, they have excellent objective (i.e., frequentist) properties, providing marvelous tools to help improve the FDA regulatory process.

Bayes Theorem↗
PubMed2005

Lipid adjustment in the analysis of environmental contaminants and human health risks.

The literature on exposure to lipophilic agents such as polychlorinated biphenyls (PCBs) is conflicting, posing challenges for the interpretation of potential human health risks. Laboratory variation in quantifying PCBs may account for some of the conflicting study results. For example, for quantification purposes, blood is often used as a proxy for adipose tissue, which makes it necessary to model serum lipids when assessing health risks of PCBs. Using a simulation study, we evaluated four statistical models (unadjusted, standardized, adjusted, and two-stage) for the analysis of PCB exposure, serum lipids, and health outcome risk (breast cancer). We applied eight candidate true causal scenarios, depicted by directed acyclic graphs, to illustrate the ramifications of misspecification of underlying assumptions when interpreting results. Statistical models that deviated from underlying causal assumptions generated biased results. Lipid standardization, or the division of serum concentrations by serum lipids, was observed to be highly prone to bias. We conclude that investigators must consider biology, biologic medium (e.g., nonfasting blood samples), laboratory measurement, and other underlying modeling assumptions when devising a statistical plan for assessing health outcomes in relation to environmental exposures.

Bias↗
PubMed2004

Marginalized binary mixed-effects models with covariate-dependent random effects and likelihood inference.

Marginal models and conditional mixed-effects models are commonly used for clustered binary data. However, regression parameters and predictions in nonlinear mixed-effects models usually do not have a direct marginal interpretation, because the conditional functional form does not carry over to the margin. Because both marginal and conditional inferences are of interest, a unified approach is attractive. To this end, we investigate a parameterization of generalized linear mixed models with a structured random-intercept distribution that matches the conditional and marginal shapes. We model the marginal mean of response distribution and select the distribution of the random intercept to produce the match and also to model covariate-dependent random effects. We discuss the relation between this approach and some existing models and compare the approaches on two datasets.

Air Pollution↗
PubMed2004

Differences in Medicare expenditures during the last 3 years of life.

OBJECTIVE: To examine age, gender, race, and area income differences in Medicare expenditures in the 3 years before death. DESIGN: Cross-sectional study. PARTICIPANTS: A random sample of aged Medicare beneficiaries who died 1996 to 1999, N = 241,047. MEASURES: We estimate differences in mean Medicare expenditures by year before death and by age, gender, race, and area income, adjusting for comorbidities and Medicaid enrollment. RESULTS: Expenditures for blacks are lower in the second and third years before death and are not significantly different from whites in the last year of life (LYOL) (y3 = 70%, P <.0001; y2 = 82%, P <.0001; LYOL = 119%, P =.098). Differences in expenditures between decedents with area incomes over $35,000 compared to under $20,000 attenuate by the LYOL (y3 = 116%, P <.0001; y2 = 107%, P <.0001; LYOL = 96%, P <.0001). Expenditure patterns for women versus men vary by age. Among the younger cohorts (68 to 74 and 75 to 79), expenditures are higher for women in all 3 years before death. This difference attenuates among older cohorts; in the oldest cohort (90+), expenditures for men exceed those for women by 11% in the LYOL (P <.0001). Older beneficiaries have higher expenditures in the second and third years before death but lower expenditures in the LYOL. On average, the youngest cohort expended $8,017 more in the LYOL relative to the oldest cohort, whereas in the third year before death, the oldest cohort's expenditures were $5,270 more than those for the youngest cohort (P <.0001). CONCLUSIONS: Age-associated differences in aggregate Medicare payments for end-of-life care are more substantial than other differences. The fact that other differences attenuate in the LYOL may reflect having overcome barriers to health care, or reflect an effective ceiling on the opportunities to provide services for persons with overwhelming illness.

Black or African American↗
PubMed2003

Cardiovascular and cerebrovascular events in patients treated for human immunodeficiency virus infection.

BACKGROUND: Metabolic abnormalities associated with human immunodeficiency virus (HIV) infection, including dysglycemia and hyperlipidemia, are increasingly prevalent, and there is concern about the possibility of an association with accelerated cardiovascular and cerebrovascular disease. METHODS: We conducted a retrospective study of the risk of cardiovascular and cerebrovascular disease among the 36,766 patients who received care for HIV infection at Veterans Affairs facilities between January 1993 and June 2001. RESULTS: For antiretroviral therapy, 70.2 percent of the patients received nucleoside analogues, 41.6 percent received protease inhibitors, and 25.6 percent received nonnucleoside reverse-transcriptase inhibitors for a median of 17 months, 16 months, and 9 months, respectively. Approximately 1000 patients received combination therapy with a protease inhibitor for at least 48 months, and approximately 1000 patients received combination therapy with a nonnucleoside reverse-transcriptase inhibitor for at least 24 months. Between 1995 and 2001, the rate of admissions for cardiovascular or cerebrovascular disease decreased from 1.7 to 0.9 per 100 patient-years, and the rate of death from any cause decreased from 21.3 to 5.0 deaths per 100 patient-years. Patient-level regression analyses indicated that there was no relation between the use of nucleoside analogues, protease inhibitors, or nonnucleoside reverse-transcriptase inhibitors and the hazard of cardiovascular or cerebrovascular events, but the use of antiretroviral drugs was associated with a decreased hazard of death from any cause. CONCLUSIONS: Use of newer therapies for HIV was associated with a large benefit in terms of mortality that was not diminished by any increase in the rate of cardiovascular or cerebrovascular events or related mortality. Fear of accelerated vascular disease need not compromise antiretroviral therapy over the short term. However, prolonged survival among HIV infected patients means that longer-term observation and analysis are required.

Adult↗
PubMed2003

DSMB case study: decision making when a similar clinical trial is stopped early.

Two similarly designed, placebo-controlled clinical trials are fully accrued and following patients for safety and outcome data. One trial is stopped at a planned interim analysis by its data safety and monitoring board (DSMB) due to a statistically significant treatment benefit. The statisticians and DSMB of the other trial are informed of these results. What are the responsibilities of the statistical center? How should the DSMB deal with the situation if the data do not support the stopped trial? What should the patients be told concerning the results of the two trials when one trial continues and the other is stopped? This DSMB case study reports on such a situation for two randomized clinical trials of oral ganciclovir for the prevention of cytomegalovirus disease in HIV/AIDS patients.

AIDS-Related Opportunistic Infections↗
PubMed2002

Fruits, vegetables, and adenomatous polyps: the Minnesota Cancer Prevention Research Unit case-control study.

Although high vegetable intakes have been associated with a lower risk of colorectal cancer, this relation is less well established for the precursor lesions, adenomatous polyps. With a case-control design involving adenomatous polyp cases (n = 564), colonoscopy-negative controls who were polyp free at colonoscopy (n = 682), and community controls (n = 535), this 1991-1994 Minnesota Cancer Prevention Research Unit study investigated the relation between fruit and vegetable consumption and first incident adenomatous polyps. Dietary intake was assessed using a food frequency questionnaire. For women, adenoma risk was approximately halved in the highest versus lowest quintile of juice consumption (cases vs. colonoscopy-negative controls: odds ratio (OR) = 0.50, 95% confidence interval (CI): 0.27, 0.92; cases vs. community controls: OR = 0.56, 95% CI: 0.30, 1.06). The association was stronger for adenomas with moderate or severe dysplasia compared with mild dysplasia. Juice was not associated with adenoma risk in men. The results for fruits, vegetables, total fruits and vegetables, green leafy vegetables, and several botanically and phytochemically defined subgroups generally were not statistically significant. Because elevated vegetable consumption has been associated with a lower risk of colorectal cancer, vegetables may have a stronger role in preventing the progression of adenomas to carcinomas rather than in preventing the initial appearance of adenomas.

Adenomatous Polyps↗
PubMed2002

Propensity score modeling strategies for the causal analysis of observational data.

Propensity score methods are used to estimate a treatment effect with observational data. This paper considers the formation of propensity score subclasses by investigating different methods for determining subclass boundaries and the number of subclasses used. We compare several methods: balancing a summary of the observed information matrix and equal-frequency subclasses. Subclasses that balance the inverse variance of the treatment effect reduce the mean squared error of the estimates and maximize the number of usable subclasses.

Journal Article↗
PubMed2002

Do patient consent procedures affect participation rates in health services research?

BACKGROUND: Few studies have examined the effects of Institutional Review Board (IRB) requirements to contact potential research participants. OBJECTIVE: To examine the association between requirements to contact potential research subjects and participation rates in a multisite health services research study. RESEARCH DESIGN, SUBJECTS: Prospective observational study of survey participation by 2673 individuals with diabetes and 1974 individuals with congestive heart failure treated at 15 clinical sites in the United States that had implemented a quality improvement intervention. MAIN OUTCOME MEASURES: Telephone survey response rates. RESULTS: Of 15 IRBs, seven required sites to obtain authorization from participants to release contact information to the study team. Five required oral and two required written advance permission. The response rate was 58% (913/1571) at sites where no advance permission was required, 39% (989/2530) from sites that required oral advance permission and 27% (145/546, P <0.001) at sites requiring written advance permission. Although 85% of eligible participants contacted directly by the study team consented to complete the survey, only 43% of individuals at sites requiring written advance permission allowed the release of contact information to the study team. CONCLUSIONS: Many potential participants did not grant advance permission to be contacted by the study team. Requiring advance permission reduced participation rates, especially at sites requiring written authorization.

Diabetes Mellitus↗
PubMed2001

Forecast of the number of patients with end-stage renal disease in the United States to the year 2010.

As the United States end-stage renal disease (ESRD) program enters the new millennium, the continued growth of the ESRD population poses a challenge for policy makers, health care providers, and financial planners. To assist in future planning for the ESRD program, the growth of patient numbers and Medicare costs was forecasted to the year 2010 by modeling of historical data from 1982 through 1997. A stepwise autoregressive method and exponential smoothing models were used. The forecasting models for ESRD patient numbers demonstrated mean errors of -0.03 to 1.03%, relative to the observed values. The model for Medicare payments demonstrated -0.12% mean error. The R(2) values for the forecasting models ranged from 99.09 to 99.98%. On the basis of trends in patient numbers, this forecast projects average annual growth of the ESRD populations of approximately 4.1% for new patients, 6.4% for long-term ESRD patients, 7.1% for dialysis patients, 6.1% for patients with functioning transplants, and 8.2% for patients on waiting lists for transplants, as well as 7.7% for Medicare expenditures. The numbers of patients with ESRD in 2010 are forecasted to be 129,200 +/- 7742 (95% confidence limits) new patients, 651,330 +/- 15,874 long-term ESRD patients, 520,240 +/- 25,609 dialysis patients, 178,806 +/- 4349 patients with functioning transplants, and 95,550 +/- 5478 patients on waiting lists. The forecasted Medicare expenditures are projected to increase to $28.3 +/- 1.7 billion by 2010. These projections are subject to many factors that may alter the actual growth, compared with the historical patterns. They do, however, provide a basis for discussing the future growth of the ESRD program and how the ESRD community can meet the challenges ahead.

Forecasting↗