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.     

Use of Indwelling Pleural Catheter in the Outpatient Management of Recurrent Malignant Pleural Effusion

IntroductionTo analyse the effectiveness and safety of the indwelling pleural catheter in the management of recurrent malignant pleural effusion.Patients and methodsA prospective multicentre study was performed in 63 consecutive outpatients from four Spanish hospitals. A total of 43 men and 20 women were included, with a median age of 67 years. In seven of the cases treatment with pleurodesis had failed; in five other cases their lung was trapped; in another five cases after repeat therapeutic thoracocentesis, and the rest of them as a preference choice to pleurodesis. All patients had an indwelling pleural catheter inserted (PleurX^®, Denver Biomedical).ResultsMost of patients (94.5%) reported an improvement in their respiratory symptoms (cough and dyspnoea) and their ability to function independently. Average length of the catheterisation was 45 days (6-222). Average amount of drained pleural effusion was 75 ml, with a frequency of drainage of between 3 and 4 times per week and once fortnightly. Spontaneous pleurodesis was achieved following 34.9% of procedures. No complications occurred during the insertion of the catheter. The post-catheterisation complications were empyema (3 cases), chest pain (2 cases), and tumour metastasis (3 cases).ConclusionsThe use of an indwelling pleural catheter is an effective palliative treatment in the outpatient management for patients suffering malignant pleural effusion. It is also a simple treatment that can be easily applied, does not require hospitalisation and can be easily managed by the patient at home, with a low rate of complications.     

Analysis of malformations of the heart amenable to a Blalock-Taussig operation

The Blalock-Taussig operation is of benefit to any patient who suffers from lack of adequate pulmonary blood flow, provided the structure of the heart is such that it is able to adjust to the altered circulation.Experience has shown that a patient with a tetralogy of Fallot can adjust to the altered circulation. The other types of malformation which have been improved by operation are those with a cardiac contour similar to that of a tetralogy of Fallot with left axis deviation, those with partial rotation of the heart on its axis, possibly those with “pure” pulmonary stenosis and an auricular septal defect, and a few with unusual arrhythmias. In atypical cases an effort is made to determine whether the condition is such that the patient can be helped by increasing the circulation to the lungs.The six criteria essential for successful operation are (1) the primary difficulty must be lack of adequate pulmonary blood flow; (2) there must be a pulmonary artery to which to anastomose the systemic artery; (3) a systemic artery must be available for the anastomosis; (4) the difference in pressure between the systemic and pulmonic circulations must be sufficiently great for blood to flow from the aorta to the lungs; (5) the structure of the lungs must be such that the patient can tolerate the collapse of one lung and the temporary occlusion of one pulmonary artery; and (6) the structure of the heart must be such that it can adjust to the altered circulation. The methods for the determination of each of these factors are discussed.In an analysis of the structure of the heart it is emphasized that (1) venous blood must be directed to the systemic circulation, (2) the increased volume of oxygenated blood which is returned from the lungs must be able to reach the aorta; (3) the structure of the heart must be such as to permit the continuous circulation of the blood at an accelerated rate; (4) the structure of the heart must also be such that the operation does not cause progressive cardiac enlargement. Each of these factors is analyzed.The effect of the altered circulation on the size of the heart is discussed in the light of the long-time results of the operation. Less than 5 per cent of the patients have shown progressive cardiac enlargement or died of cardiac failure. Thirty per cent have shown no increase in heart size. Thirty per cent have shown increase in heart size during the first three weeks after operation and then have adjusted to the load, and 30 per cent have shown cardiac enlargement between the time of discharge and the six-month checkup and thereafter have shown no further increase in heart size.In general, the results from the use of the subclavian artery, as estimated by the oxygen saturation of the arterial blood, the red blood cell count, and the hemoglobin level, have been as beneficial as when the innominate artery has been used for the anastomosis and, moreover, this former group of patients has shown less increase in the size of the heart.A child with a tetralogy of allot has a 90 per cent chance of being greatly improved by the operation and an equally good chance of maintaining that improvement.