Multiple imputation for simple estimation of the hazard function based on interval censored data.

A data augmentation algorithm is presented for estimating the hazard function and pointwise variability intervals based on interval censored data. The algorithm extends that proposed by Tanner and Wong for grouped right censored data to interval censored data. It applies multiple imputation and local likelihood methods to obtain smooth non-parametric estimates for the hazard function. This approach considerably simplifies the problem of estimation for interval censored data as it transforms it into the more tractable problem of estimation for right censored data. The method is illustrated for two real data sets: times to breast cosmesis deterioration and times to HIV-1 infection for individuals with haemophilia. Simulations are presented to assess the effects of various parameters on the estimates and their variances.

Goodness-of-fit for GEE: an example with mental health service utilization.

Suppose we use generalized estimating equations to estimate a marginal regression model for repeated binary observations. There are no established summary statistics available for assessing the adequacy of the fitted model. In this paper we propose a goodness-of-fit test statistic which has an approximate chi-squared distribution when we have specified the model correctly. The proposed statistic can be viewed as an extension of the Hosmer and Lemeshow goodness-of-fit statistic for ordinary logistic regression to marginal regression models for repeated binary responses. We illustrate the methods using data from a study of mental health service utilization by children. The repeated responses are a set of binary measures of service use. We fit a marginal logistic regression model to the data using generalized estimating equations, and we apply the proposed goodness-of-fit statistic to assess the adequacy of the fitted model.

Surveillance of vaccine-related adverse events in the first year of life: a Manitoba cohort study.

This study used data from the population database through which the province of Manitoba, Canada, administers its universal health insurance plan. Enrollment, hospitalization, and immunization files from children born in the 1987-1989 period were linked using the unique identification number assigned to each population member. Analysis of these linked data successfully identified serious potential adverse events in the first year of life and the timing of events around immunization. Not only is population-based active surveillance for immunization-related events feasible, but the techniques described, applied to years of data accumulated through surveillance, offer powerful research tools. Baseline population incidences of adverse events were calculated, temporal relationships between events and immunization assessed, and incidences for events showing true temporal associations determined. Eventual goals are the quantification of vaccine-related risk and the gathering of evidence concerning casual associations. The approach could be used readily by several other Canadian provinces and by health maintenance organizations in the United States.

Outcomes of coronary artery bypass graft surgery in 24,461 patients aged 80 years or older.

BACKGROUND: Coronary artery bypass graft surgery is increasingly common in patients of age > or = 80 years. Single-institution reviews have cited a wide range of mortality results after bypass surgery in this age group, in part because of limited sample sizes. Using claims data, we examined recent national trends in the use and outcomes of bypass surgery in the very elderly. METHODS AND RESULTS: From an examination of Medicare data from 1987 through 1990, we identified 24,461 patients of age > or = 80 years who underwent bypass surgery. We compared surgical outcomes in these patients with those in Medicare patients of age 65 to 70 years. We found that the national use of bypass surgery in patients of age > or = 80 years increased 67% between 1987 and 1990. Compared with patients of age 65 to 70 years, the very elderly had significantly longer postoperative hospital stays (mean, 14.3 versus 10.4 days), higher charges (mean, $48,200 versus $38,000), and greater costs (mean, $27,200 versus $21,700). In-hospital (11.5% versus 4.4%), 1-year (19.3% versus 7.9%), and 3-year mortality rates (28.8% versus 13.1%) after bypass surgery were also significantly higher in patients of age > or = 80 years compared with younger patients. Although their initial surgical risk was high, octogenarians who underwent bypass surgery had a long-term survival rate similar to that of the general US octogenarian population. CONCLUSIONS: The use of bypass surgery in patients of age > or = 80 years in increasing. These very elderly patients face high surgical risks and accumulate significant hospital expenses. Further research is indicated to determine whether the long-term benefits from bypass surgery in the very elderly outweigh the increased procedural risks.

Changes in mortality after myocardial revascularization in the elderly. The national Medicare experience.

OBJECTIVE: To examine secular changes in the use and outcome of percutaneous transluminal coronary angioplasty and cardiac bypass graft surgery in the elderly. DESIGN: A retrospective cohort study based on a longitudinal database created from the administrative files of Medicare. SETTING: U.S. hospitals that perform myocardial revascularization procedures covered by Medicare. PATIENTS: 225,915 consecutive patients who had angioplasty and 357,885 consecutive patients who had bypass surgery from 1987 to 1990. MEASUREMENTS: The rates of angioplasty and bypass surgery use; unadjusted 30-day and 1-year mortality rates after revascularization; and adjusted odds ratios for mortality by year of procedure for 1987 to 1990. RESULTS: From 1987 to 1990, the rates of angioplasty and bypass surgery done in the elderly increased by 55% and 18%, respectively. During this period, 30-day unadjusted mortality rates after angioplasty and bypass surgery decreased by 25% (95% CI, 22% to 28%) and 12% (CI, 10% to 14%), and 1-year mortality rates decreased by 10% (CI, 8% to 11%) and 8% (CI, 7% to 10%), respectively. After adjustment for changes in patient characteristics, 30-day mortality rates after these procedures decreased by 37% (CI, 32% to 41%) and 18% (CI, 14% to 21%), and 1-year mortality rates decreased by 22% (CI, 18% to 25%) and 19% (CI, 16% to 21%), respectively. CONCLUSIONS: The use of cardiac revascularization procedures in the elderly has steadily increased. Patients who had revascularization are progressively older, have more coded comorbid conditions, and present with more acute diseases. Although elderly patients have apparently higher risk profiles, mortality rates after angioplasty and bypass surgery in the elderly have decreased, suggesting a national improvement in the outcomes of these interventions. Health policy decisions concerning revascularization procedures in the elderly must consider these trends in improved outcome.

Monitoring childhood immunizations: a Canadian approach.

In Manitoba, Canada, a centralized, computerized childhood immunization monitoring system serves a population with insured medical coverage; each individual has a unique identification number. All physicians bill a single payer, and specific billing codes are used to identify immunizations given by physicians and by public health nurses. Together with dates of service, this information is used to construct immunizations-to-date and age-at-immunization profiles for individuals and groups. Reminders seeking missing information are built into the system and executed at strategic ages. The quality of input data has been assessed as high. The approach could be used readily by health maintenance organizations in the United States.