Likelihood-based analysis of longitudinal data from outcome-related sampling designs.

Investigators commonly gather longitudinal data to assess changes in responses over time and to relate these changes to within-subject changes in predictors. With rare or expensive outcomes such as uncommon diseases and costly radiologic measurements, outcome-dependent, and more generally outcome-related, sampling plans can improve estimation efficiency and reduce cost. Longitudinal follow up of subjects gathered in an initial outcome-related sample can then be used to study the trajectories of responses over time and to assess the association of changes in predictors within subjects with change in response.

Patterns of family doctor decision making in practice context. What are the implications for medical practice variation and social disparities?

Medical practice variation and social disparities in health are pervasive features of health care systems. But what impact might everyday clinical decision making have in shaping such aggregate patterns, and could this in turn be influenced by the immediate environment in which family doctors practise? We investigate this by studying inter-practitioner variation in clinical activity across four payment types in New Zealand, a "gatekeeper" primary care system. We do this for four measures of clinical activity by patient ethnic and socio-economic status in a 2001/2002 representative sample of 9272 encounters at 185 family practices.

Partial likelihood ratio tests for the Cox model under complex sampling.

We develop an analog of the likelihood ratio test for Cox proportional hazards models fitted to sample survey data. We look at methods for computing the asymptotic distribution and at ways of improving the small-sample performance. The methods are illustrated with examples using data from the National Health and Nutrition Examination Survey and from a stratified case-cohort study.

A Hardy-Weinberg equilibrium test for analyzing population genetic surveys with complex sample designs.

Testing for deviations from Hardy-Weinberg equilibrium is a widely recommended practice for population-based genetic association studies. However, current methods for this test assume a simple random sample and may not be appropriate for sample surveys with complex survey designs. In this paper, the authors present a test for Hardy-Weinberg equilibrium that adjusts for the sample weights and correlation of data collected in complex surveys.

Using multiple frames in health surveys.

In this paper, we look at a unified approach to estimation in multiple frame surveys that enables the analysis to be handled with standard survey software. We investigate how the approach performs with data from the Auckland Diabetes, Heart and Health Survey, a dual frame survey looking at risk factors for cardiovascular disease with special attention to Maori and Pacific Island people and to older people. The results suggest that the use of multiple frames might be useful in other surveys where good estimates are wanted for both the whole population and particular subgroups at the same time.

Case-control analysis with a continuous outcome variable.

It is not uncommon for a continuous outcome variable Y to be dichotomized and analysed using logistic regression. Moser and Coombs (Statist. Med.

Do hospital bed reduction and multiple system reform affect patient mortality?: A trend and multilevel analysis in New Zealand over the period 1988-2001.

Background: The impact of hospital and system restructuring on the quality and pattern of care is an important issue of public policy concern.

Objective: To assess the effect on patterns of care and patient outcomes of a substantial reduction in public hospital bed availability and multiple reorganizations in New Zealand through the 1990s.

Research Design: Trend analysis using both tabular and multilevel techniques.

On the Breslow-Holubkov estimator.

Breslow and Holubkov (J Roy Stat Soc B 59:447-461 1997a) developed semiparametric maximum likelihood estimation for two-phase studies with a case-control first phase under a logistic regression model and noted that, apart for the overall intercept term, it was the same as the semiparametric estimator for two-phase studies with a prospective first phase developed in Scott and Wild (Biometrica 84:57-71 1997). In this paper we extend the Breslow-Holubkov result to general binary regression models and show that it has a very simple relationship with its prospective first-phase counterpart. We also explore why the design of the first phase only affects the intercept of a logistic model, simplify the calculation of standard errors, establish the semiparametric efficiency of the Breslow-Holubkov estimator and derive its asymptotic distribution in the general case.

Quality of hospital care for Māori patients in New Zealand: retrospective cross-sectional assessment.

Background: New Zealand has a substantial indigenous minority--the Māori--that has considerably worse health status than the majority population. We aimed to assess possible disparities in quality of hospital care for Māori with data on preventable adverse events as an indicator of suboptimum treatment.

Methods: We undertook a nationally representative cross-sectional survey of admissions to general public hospitals with more than 100 beds providing acute care.

Modeling eligibility under national systems of compensation for treatment injury.

How can different schemes of compensation for treatment injury be evaluated? This article offers an empirical approach to assessment based on the simulation of alternative models of eligibility using real-world data. It draws on information about adverse events generated from a representative survey of public hospital admissions in New Zealand and classifies these under a range of eligibility criteria for different possible compensation systems. These are then evaluated according to a number of policy design considerations, using variables available from the New Zealand study.

Secondary analysis of case-control data.

We extend the discussion of Lee et al. and others on methods for performing secondary analyses of case-control sampled data and carry out an extensive investigation of efficiency and robustness. We find that, with the exception of the 'analyse-the-controls-only' strategy for populations in which cases are rare, ad hoc methods in common usage often lead to extremely misleading conclusions and that it is not possible to tell in advance when this will happen.

Adverse events in New Zealand public hospitals II: preventability and clinical context.

Aims: To assess the preventability and clinical context of adverse events identified in New Zealand public hospitals.

Methods: Two-stage retrospective review of 6579 medical records randomly sampled from admissions for 1998 in 13 generalist hospitals providing acute care. Initial screening and medical review according to a standardised protocol.

Adverse events in New Zealand public hospitals I: occurrence and impact.

Aim: To assess the occurrence and impact of adverse events in New Zealand public hospitals.

Methods: Two-stage retrospective review of 6579 medical records, selected by systematic list sample from admissions for 1998 in 13 generalist hospitals providing acute care. After initial screening, medical records were reviewed by trained medical practitioners using a standardised protocol.

How much variation in clinical activity is there between general practitioners? A multi-level analysis of decision-making in primary care.

Objectives: There is considerable policy interest in medical practice variation (MPV). Although the extent of MPV has been quantified for secondary care, this has not been investigated adequately in general practice. Technical obstacles to such analyses have been presented by the reliance on ecological small area variation (SAV) data, the binary nature of many clinical outcomes in primary care and by diagnostic variability.

Co-morbidity and health outcomes in three Auckland hospitals.

Aims: To establish the burden of co-morbid disease using the Charlson Index among hospital inpatients and its relationship to key health outcomes.

Methods: An initial screen was carried out on 1575 medical records selected by systematic list sample from admissions for 1995 in three public hospitals in the Auckland region. In the course of the administration of the instrument, screeners were required to record the occurrence of co-morbid disease using the Charlson Index.