Multivariate modelling of responses to conditional items: New possibilities for latent class analysis

Questionnaire data may contain missing values because certain questions do not apply to all respondents. For instance, questions addressing particular attributes of a symptom, such as frequency, triggers or seasonality, are only applicable to those who have experienced the symptom, while for those who have not, responses to these items will be missing. This missing information does not fall into the category ‘missing by design’, rather the features of interest do not exist and cannot be measured regardless of survey design. Analysis of responses to such conditional items is therefore typically restricted to the subpopulation in which they apply. This article is concerned with joint multivariate modelling of responses to both unconditional and conditional items without restricting the analysis to this subpopulation. Such an approach is of interest when the distributions of both types of responses are thought to be determined by common parameters affecting the whole population. By integrating the conditional item structure into the model, inference can be based both on unconditional data from the entire population and on conditional data from subjects for whom they exist. This approach opens new possibilities for multivariate analysis of such data. We apply this approach to latent class modelling and provide an example using data on respiratory symptoms (wheeze and cough) in children. Conditional data structures such as that considered here are common in medical research settings and, although our focus is on latent class models, the approach can be applied to other multivariate models. Copyright © 2009 John Wiley & Sons, Ltd.     

早期糖尿病视网膜病变药物治疗的药物经济学分析

目的：探讨不同方案治疗早期糖尿病视网膜病变的经济效果,找出既经济又有效的方案。方法：对目前临床常用的4种不同治疗方案（导升明、胰激肽原酶、复方血栓通胶囊、复方丹参滴丸,治疗时间均为90d）运用药物经济学方法进行成本-效果分析。结果：4种方案所需费用分别为1417.50元、810.00元、891.00元、656.10元;治疗有效率分别为94.25%、85.09%、85.17%、83.53%;成本-效果比分别为15.04、9.52、10.46、7.85。结论：复方丹参滴丸治疗效果较好,不良反应少,成本低廉。     

结节性甲状腺肿合并其他甲状腺疾病临床分析

目的探讨结节性甲状腺肿合并其他甲状腺疾病的临床特点。方法回顾性分析我院手术治疗的4622例结节性甲状腺肿中并存其他甲状腺疾病的临床资料。结果4622例结节性甲状腺肿中700例合并其他甲状腺疾病，1418例存在不同的诊断失误。结论在诊断结节性甲状腺肿的同时应注意其合并的其他甲状腺疾病。     

One‐ and two‐stage design proposals for a phase II trial comparing three active treatments with control using an ordered categorical endpoint

Phase II clinical trials are performed to investigate whether a novel treatment shows sufficient promise of efficacy to justify its evaluation in a subsequent definitive phase III trial, and they are often also used to select the dose to take forward. In this paper we discuss different design proposals for a phase II trial in which three active treatment doses and a placebo control are to be compared in terms of a single‐ordered categorical endpoint. The sample size requirements for one‐stage and two‐stage designs are derived, based on an approach similar to that of Dunnett. Detailed computations are prepared for an illustrative example concerning a study in stroke. Allowance for early stopping for futility is made. Simulations are used to verify that the specified type I error and power requirements are valid, despite certain approximations used in the derivation of sample size. The advantages and disadvantages of the different designs are discussed, and the scope for extending the approach to different forms of endpoint is considered. Copyright © 2008 John Wiley & Sons, Ltd.     

Measurement in clinical trials: A neglected issue for statisticians?

Biostatisticians have frequently uncritically accepted the measurements provided by their medical colleagues engaged in clinical research. Such measures often involve considerable loss of information. Particularly, unfortunate is the widespread use of the so‐called ‘responder analysis’, which may involve not only a loss of information through dichotomization, but also extravagant and unjustified causal inference regarding individual treatment effects at the patient level, and, increasingly, the use of the so‐called number needed to treat scale of measurement. Other problems involve inefficient use of baseline measurements, the use of covariates measured after the start of treatment, the interpretation of titrations and composite response measures. Many of these bad practices are becoming enshrined in the regulatory guidance to the pharmaceutical industry. We consider the losses involved in inappropriate measures and suggest that statisticians should pay more attention to this aspect of their work. Copyright © 2009 John Wiley & Sons, Ltd.     

Is the political system really related to health?

We analyze whether the political system and its stability are related to cross-country differences in health. We apply factor analysis on various national health indicators for a large sample of countries over the period 2000–2005 and use the outcomes of the factor analysis to construct two new health measures, i.e., the health of individuals and the quality of the health care sector. Using a cross-country structural equation model with various economic and demographic control variables, we examine the relationship between the type of regime and political stability on the one hand and health on the other. The political variables and the control variables are measured as averages over the period 1980–1999. Our results suggest that democracy has a positive relationship with the health of individuals, while regime instability has a negative relationship with the health of individuals. Government instability is negatively related to individual health via its link with the quality of the health care sector, while democracy is positively related with individual health through its link with income. Our main findings are confirmed by the results of a panel model and various sensitivity tests.     

Foot Polydactyly and Polysyndactyly: Genetic Implications in Two Families

The purpose of this study was to determine the genetic characteristics of foot polydactyly and identify its inheritance pattern by analyzing familial pedigree. Five cases from 2 Korean families were studied: 1 is a family whose members have been affected for 4 generations and the other for 2 generations. Using peripheral blood samples, we performed chromosomal analysis using the banding technique with Giemsa stain and karyotyping. We investigated the shape and structure of 46 chromosomes, looking for translation, deletion, inversion, ring chromosome, and isochromosome abnormalities. All peripheral blood samples demonstrated no chromosomal abnormalities, though the genetic nature of foot polydactyly and a new genetic locus was identified recently by other studies. Familial pedigree analysis suggested that polydactyly was inherited as an autosomal dominant trait in the first family. The mode of inheritance for the second family could not be determined due to an insufficient number of family members. The result of this study brought us to the conclusion that, while genetic factors play a major role in polydactyly, other factors may contribute to its occurrence.     

胃粘膜癌前病变的形态定量研究——胃粘膜核腺比值的定量分析

应用自动化图象分析仪对131个胃粘膜肠型病灶(单纯性肠化27个;异型增生:轻度30,中度35个,重度20个;肠型胃癌19个)进行定量分析。以单个腺管内细胞核总面积与细胞面积之比(ING)作为反映细胞核大小、数量及覆层排列程度的客观定量指标。结果发现:单纯性肠化(对照组)0.165±0.025,轻度异型增生0.21±0.023,中度异型增生0.259±0.026,重度异型增生0.32±0.028,分化型胃癌0.371±0.052,各组ING值呈正态,各组间的均值有非常显著的差异(P<0001)。因而,ING可作为胃粘膜癌前病变诊断的指标。