Estimation of Hazard, Density and Survivor Functions for Randomly Censored Data

Maximum likelihood estimation and goodness-of-fit techniques are used within a competing risks framework to obtain maximum likelihood estimates of hazard, density, and survivor functions for randomly right-censored variables. Goodness-of- fit techniques are used to fit distributions to the crude lifetimes, which are used to obtain an estimate of the hazard function, which, in turn, is used to construct the survivor and density functions of the net lifetime of the variable of interest. If only one of the crude lifetimes can be adequately characterized by a parametric model, then semi-parametric estimates may be obtained using a maximum likelihood estimate of one crude lifetime and the empirical distribution function of the other. Simulation studies show that the survivor function estimates from crude lifetimes compare favourably with those given by the product-limit estimator when crude lifetimes are chosen correctly. Other advantages are discussed.     

Net worth and the economic diversity of the elderly

Using data from the 1984 panel of the Survey of Income and Program Participation (SIPP), this article examines characteristics of the older population disaggregated by net-worth quintiles. The authors argue that income is not a sufficient measure of economic status for current policy discussions on issues such as changing Medicare co-payments, increasing the taxation of social security benefits, or means-testing under Medicaid. Net worth is a better measure of economic status, particularly for the elderly, because it represents the net value of assets accumulated over the life course. Their results indicate that there is considerable diversity in the economic status of the older population, which is masked by aggregate statistics (such as means and medians) typically used to summarize the economic status of population groups. Stereotypical views of the elderly based on such aggregates result in misdirected policy formulation. In the future, policymakers will need to formulate policies and programs using information on the distributions of income and assets among the older populations rather than relying on statistical aggregates.     

Fossil fuel supplies simulation 1972–1979

Fossil fuels are an important source of energy for Ontario Hydro and purchases exceed $100 million per year. This paper describes a computer simulation of the inventory situation over an eight-year period, which is being used to assess the relationship between order flexibility and the target carry-over stocks at the beginning of each shipping season. A simple way of presenting the results for management evaluation is illustrated. Variations of the model are used to assess random influences, such as strikes, and to determine the economic balance between holding costs and stock-outs.     

What do the parents of tomorrow know about child care? A survey of 14–16 year olds

What do the parents of tomorrow know about child care? This study aimed to obtain a baseline measurement of child care knowledge, to ascertain any differences in knowledge between adolescents with and without mild to moderate learning difficulties (MLD). In addition, we were interested to establish the effect of school nurse health education health input on knowledge in the learning difficulties subgroup. Assessment was by self‐completed questionnaire and interview of a random sample of 14–16 year olds attending mainstream and special schools. Sixty pupils from secondary school and 33 from a MLD school took part in the study. Pupil knowledge in basic parenting and child care was dependent on the type of school attended, reading ability of those attending the MLD school and the provision of health education in the special school by the school nurse. No associations were found between pupils knowledge and their gender, family position or family size. Pupils from both schools scored lower in the areas of health service organisation and personnel, health promotion and management of common childhood conditions. Adolescents have insufficient knowledge of basic child care and services available for new parents. The effect of school based health education in these areas is promising. Copyright © 2001 John Wiley & Sons, Ltd.     

全系列三维激光扫描技术在文物及考古测绘中的应用

三维激光扫描技术在文物及考古测绘中的综合应用,实现了文物及考古测绘由二维向三维、四维、乃至多维的革命性飞跃。在大量测绘实践和分析研究基础上,文章对微观、中观、宏观等全系列三维激光扫描仪在文物与考古测绘中的应用相关问题进行了梳理,根据文物及考古测绘特点探讨了基于三维激光扫描技术的文物考古测绘成果多样化表现形式;进一步指出,将传统测量方法和先进测量技术融合贯通、优势互补是全系列三维激光扫描技术深度应用的基本途径。     

Percentage points for directional anderson-darling goodness-of-fit tests

This paper discusses the problem of assessing the asymptotic distribution when parameters of the hypothesized distribution are estimated from a sample, pointing out a common mistake included in the paper by Sinclair, Spurr, and Ahmad (1990) which introduced two modifications of the Anderson-Darling goodness-of-fit test statistic. Their two test statistics modify the popular Anderson-Darling test statistic to be sensitive to departures of the fitted distribution from the true distribution in one or the other of the tails. This paper uses these new test statistics to develop tests of fit for the normal and exponential distributions. Easy to use formulas are given so the reader can perform these tests at any sample size without consulting exhaustive tables of percentage points. Finally a power study is given to demonstrate the test statistics’ viability against a broad range of alternatives.     

A new look at the health and homeless experience of a cohort of five-year olds

Homelessness is increasing and health workers and others need to be ever vigilant about the risk that this has on children's health. What is that risk and what are children's experiences of homelessness? A retrospective case note study was carried out to compare the health of a group of five-year olds who had experienced homelessness and compare them with matched ‘non-homeless’ controls. A home interview questionnaire was used to give a profile of the children's housing experience and the health issues faced during their time in temporary accommodation. Fifty-three cases when compared with 41 controls showed a statistically greater prevalence of child protection issues and an increased number of health needs identified at the school nurse health appraisal. The housing profile identified that the case children moved homes many times (37 per cent more than five times), were homeless much longer than the officially registered period (67 per cent more than 12 months) and 61 per cent were made homeless through domestic violence. The study reinforces the need for us to acknowledge important environmental stress and to continue to advocate for this group of disadvantaged children.     

Decomposition analysis as a framework for understanding heterogeneity of treatment effects in non-randomized health care studies

This paper uses the decomposition framework from the economics literature to examine the statistical structure of treatment effects estimated with observational data compared to those estimated from randomized studies. It begins with the estimation of treatment effects using a dummy variable in regression models and then presents the decomposition method from economics which estimates separate regression models for the comparison groups and recovers the treatment effect using bootstrapping methods. This method shows that the overall treatment effect is a weighted average of structural relationships of patient features with outcomes within each treatment arm and differences in the distributions of these features across the arms. In large randomized trials, it is assumed that the distribution of features across arms is very similar. Importantly, randomization not only balances observed features but also unobserved. Applying high dimensional balancing methods such as propensity score matching to the observational data causes the distributional terms of the decomposition model to be eliminated but unobserved features may still not be balanced in the observational data. Finally, a correction for non-random selection into the treatment groups is introduced via a switching regime model. Theoretically, the treatment effect estimates obtained from this model should be the same as those from a randomized trial. However, there are significant challenges in identifying instrumental variables that are necessary for estimating such models. At a minimum, decomposition models are useful tools for understanding the relationship between treatment effects estimated from observational versus randomized data.     

Assessing and communicating heterogeneity of treatment effects for patient subpopulations: Panel discussion on considerations in design and analysis

Clinical trials are primarily conducted to understand the average effects treatments have on patients. However, patients are heterogeneous in the severity of the condition and in ways that affect what treatment effect they can expect. It is therefore important to understand and characterize how treatment effects vary. The design and analysis of clinical studies play critical roles in evaluating and characterizing heterogeneous treatment effects. This panel discussed considerations in design and analysis under the recognition that there are heterogeneous treatment effects across subgroups of patients. Panel members discussed many questions including: What is a good estimate of the treatment effect in me, a 65-year-old, bald, Caucasian-American, male patient? What magnitude of heterogeneity of treatment effects (HTE) is sufficiently large to merit attention? What role can prior evidence about HTE play in confirmatory trial design and analysis? Is there anything described in the 21st Century Cures Act that would benefit from greater attention to HTE? An example of a Bayesian approach addressing multiplicity when testing for treatment effects in subgroups will be provided. We can do more or better at understanding heterogeneous treatment effects and providing the best information on heterogeneous treatment effects.