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.     

Congestive gastropathy

15 patients with congestive gastropathy were reported including clinical and pathological characteristics of the disease. Every patient had alcoholic liver cirrhosis and portal hypertension. 6 patient's stomach was resected while in 2 further cases the disease was found at autopsy. In additional 7 cases the characteristic microvascular changes were observed in endoscopic biopsy specimens from the gastric mucosa. The authors presume that this disease has an acute and a chronic stage. In the acute stage dilated capillaries are present under the surface, not related to the inflammation of gastric mucosa. This phenomenon was described in the literature. In the chronic stage there are dilated and tortuous vessels in the submucosal layer surrounded by collagenous connective tissue. The authors suppose that the thick and fibrotic submucosal layer causes microcirculatory disturbances in the gastric mucosa. The impaired microcirculation may cause extensive ulcers with profuse and sometimes lethal bleeding.     

Health and social inequities in Switzerland

Despite standards of living and life expectancy amongst the highest in Europe, Switzerland exhibits fairly substantial social inequities in health. As regards male mortality by socio-economic group, these differentials are both marked and independent of cause of death. There is a wealth of information on morbidity and disability supporting the hypothesis that people in lower socio-economic groups tend to age faster and suffer more at younger ages. It is similarly evident that infants of low class mothers, particularly those unwed, underprivileged immigrant, are at excess risk. The Swiss results are of political and scientific interest in that they suggest that the average wealth of a community does not determine health differentials.     

The use of measures of influence in epidemiology

In epidemiological studies the units of observation often consist of political entities such as countries, each of which has its own specific inner structure. When a multiple regression is performed it is therefore of particular interest to analyse not only the overall behaviour of the dataset, but in addition, to investigate how each individual country contributes to, and deviates from, this overall behaviour. By means of the example 'relation between infant mortality and structural data of countries' several ways are discussed of how each individual country can influence the regression model. Firstly the potential influence which each country might exhibit due to the explanatory variables alone is analysed. Then the actual influence of each country is analysed by taking the explanatory variables and the target variable into account simultaneously. This is done by means of statistical measures not generally familiar to epidemiologists, which have been developed in recent years (leverage values, Cook's distances). These measures also point to deviations of countries from the model, and suggest directions in which to search for explanation. Finally the influence of the 'size' of the countries is investigated.     

Isolated leukemic iritis in childhood

Case report on a child with acute lymphogenous leukemia. Although there was constant hematological remission she developed an isolated leukemic iritis and secondary glaucoma. The clinical picture showed a characteristic stratification of the hyphema. After the patient had remained seated for a prolonged period of time the leukemic cells settled above the erythrocytes, forming a so-called pseudohypopyon, which diagnostically important. Cytologic examination after anterior chamber paracentesis is indispensable in order to establish the etiology of the disease. Isolated leukemic iritis may be the first sign of a relapse and therefore indicate a need to reinstitute induction therapy.     

Malignant pleural mesothelioma among Swiss furniture workers. A new high-risk group

Within the framework of a research project concerning occupational mortality, attention was drawn to a highly significant standardized mortality ratio for mesothelioma among furniture workers. From information drawn from the mortality records for the years 1979-1985 and from the 1980 national census, the number of pleural mesotheliomas among this occupational group was examined. The expected number of deaths from pleural mesothelioma among Swiss furniture workers for this period was 4.4; the observed number was 12. This finding indicates a 2.7-fold relative risk (P = 0.004) for death due to these cancers among Swiss furniture workers.     

The relationship between anti-human eye muscle antibodies and thyroid function, anti-TSH receptor antibodies and eye symptoms in Graves' ophthalmopathy.

Circulating IgG, IgA, and IgM antibodies to human eye muscle cytosol antigens were studied in 60 patients with Graves' ophthalmopathy using the indirect ELISA method. There was a significant difference in the levels of both IgG and IgA antibodies between the patients with Graves' ophthalmopathy and a control group (p < 0.001). IgA antibodies to eye muscle cytosol antigens were raised in 20 out of 29 patients with proptosis (class 3 ophthalmopathy), in comparison with 31 patients out of the total group of 60 with Graves' ophthalmopathy (p < 0.02). Anti-TSH receptor antibodies (TRAK) were not present in over half of the 31 patients with raised IgA antibodies to eye muscle antigens. However, a significant difference was found between the levels of IgG and IgA antibodies in the TRAK-negative patients (p < 0.05). These findings suggests that both IgG and IgA antibodies to eye muscle antigens might be important in the development of ophthalmopathy.     

Simple non-radioactive detection of the CFTR mutation N1303K by artificial creation of a restriction site.

N1303K is one of the most frequent non-delta F508 mutations causing cystic fibrosis in Central Europe. Since no restriction site is altered by this mutation and no other frequent mutations are known so far in exon 21, the detection requires a separate and laborious test. A mismatched primer was used to create an artificial Hin dIII site in amplified wildtype DNA, which is destroyed by the mutation. This allows for rapid and convenient detection by restriction enzyme digestion.