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One method for analyzing contingency tables with missing observations is to model the missing-data mechanism using log-linear models. Previous methods for obtaining estimates (of missing counts and parameters) have required an iterative algorithm. In many cases, however, one can obtain estimates by use of a simple algebraic formula. We illustrate the method with data on smoking and birth weight.
BACKGROUND: There may be a link between infection and preterm birth. OBJECTIVES: Since rupture of the membranes is an important factor in the progression of preterm labour, it is important to see if antibiotics are of any benefit prior to membrane rupture. The objective of this review was to assess the effects of antibiotics administered to women in preterm labour with intact membranes, on maternal and neonatal outcomes. SEARCH STRATEGY: We searched the Cochrane Pregnancy and Childbirth Group trials register and reference lists of articles. We contacted experts in the field. SELECTION CRITERIA: Randomised trials which compared antibiotic treatment with placebo or no treatment for women in preterm labour (between 20 and 36 weeks gestation) with intact membranes. DATA COLLECTION AND ANALYSIS: Trial quality was assessed and data were extracted independently by two reviewers. Study authors were contacted for missing data. MAIN RESULTS: Meta-analysis of the ten included trials demonstrated a statistically significant prolongation of pregnancy associated with the use of antibiotics (5. 4 days, 95% confidence interval (CI) 0.9- 9.8 days). Antibiotic treatment was also associated with a statistically significant reduction in maternal infection (odds ratio (OR) 0.59, 95% CI 0.36, 0.97) and neonatal necrotising enterocolitis (OR 0.33, 95% CI 0.13, 0.88). No statistically significant effect was detected on the neonatal outcomes of respiratory distress syndrome and neonatal sepsis, although there was a trend towards the latter (OR 0.67, 95% CI 0.42, 1.07). An increase in perinatal mortality was observed in the group receiving antibiotics (OR 3.36, 95% CI 1.21, 9.32). REVIEWER'S CONCLUSIONS: Although a prolongation in time to delivery and a trend towards a reduction in neonatal sepsis was detected, this review fails to demonstrate a clear overall benefit from antibiotic treatment for preterm labour with intact membranes on neonatal outcomes and raises concerns about increased perinatal mortality for those who received antibiotics. This treatment cannot therefore be currently recommended for routine practice. Further research is required to identify a subgroup of women (and their babies) who are more likely to experience benefit from antibiotic treatment for preterm labour prior to membrane rupture, and to identify which antibiotic or combination of antibiotics is most effective. The results of the ongoing ORACLE trial should help resolve some of the uncertainties revealed by this review.
BACKGROUND: Treatment of acute asthma is based on rapid reversal of bronchospasm and arresting airway inflammation. There is some evidence that intravenous magnesium can provide additional bronchodilation when given in conjunction with standard bronchodilating agents and corticosteroids. No systematic review of this literature has been completed on this topic. OBJECTIVES: To examine the effect of additional intravenous magnesium sulfate in patients with acute asthma managed in the emergency department. SEARCH STRATEGY: Randomised controlled trials were identified from the Cochrane Airways Review Group register. Bibliographies from included studies, known reviews and texts were searched. Primary authors and content experts were contacted. SELECTION CRITERIA: Randomised controlled trials or quasi-randomised trials were eligible for inclusion. Studies were included if patients presented with acute asthma and were treated with IV magnesium sulfate vs placebo. DATA COLLECTION AND ANALYSIS: Data were extracted and methodological quality was assessed independently by two reviewers. Missing data were obtained from authors. MAIN RESULTS: Seven trials were included (5 adult, 2 pediatric). A total of 665 patients were involved. Patients receiving magnesium sulfate demonstrated non-significant improvements in peak expiratory flow rates when all studies were pooled (weighted mean difference: 29.4 L/min; 95% confidence interval: -3.4 to 62). In studies of people with severe acute asthma, peak expiratory flow rate improved by 52.3 L/min (95% confidence interval: 27 to 77.5). The forced expiratory volume in one second also improved by 9.8 % predicted (95% confidence interval: 3.8 to 15.8). Overall, admission to hospital was not reduced, odds ratio: 0.31 (95% confidence interval: 0.09 to 1.02). In the severe subgroup, admissions were reduced in those receiving magnesium sulfate (odds ratio: 0.10, 95% confidence interval: 0.04 to 0.27). No clinically important changes in vital signs or adverse side effects were reported. REVIEWER'S CONCLUSIONS: Current evidence does not support routine use of intravenous magnesium sulfate in all patients with acute asthma presenting to the emergency department. Magnesium sulfate appears to be safe and beneficial in patients who present with severe acute asthma.
Lung function tests are used both clinically, in assessing disease, and epidemiologically, in identifying those factors which influence the growth and aging process of the lungs. The user must beware of several common pitfalls in the use of these tests, however. First, the commonly used tests of lung function can only identify patterns of dysfunction, not specific pathologic processes. Second, these tests are subject to many sources of intra- and inter-subject variability, making it difficult to dissect out the signal (for example, the rate of lung aging in adults) from the noise which may greatly exceed the signal. Finally, the analysis of longitudinal pulmonary function data is complicated by the alinearity of the growth and aging process, missing data, variable follow-up times, information censoring mechanisms and covariate processes, and problems in defining abnormality.
Clinical trials involving quality of life measurement published in the literature suffer from important weaknesses due to the lack of information on numerous topics. The psychometric properties of the instruments are often lacking as well as data on the number of patients treated and analyzed. The handling of missing data is rarely documented. In order to facilitate the reporting of trials and the evaluation of published results, this article proposes a set of general guidelines for the reporting of clinical trials which include a quality of life assessment. A checklist designed to assist authors is appended.
One hundred and eight pregnant women, most of their husbands and a comparison group of non-expectant parents were recruited for a long-term study which involved responding to a 55-item Symptom Checklist (SCL) and the Beck Depression Inventory three times during pregnancy and once during the first postpartum month. Responses to the SCL were factor analysed, and the four groups were then compared on their factor scores as well as their scores on the Beck Depression Inventory (BDI) using discriminant analysis and trend analysis. The discriminant analyses were done twice: once using all the data provided by all subjects and once using only subjects with no missing data. At each measurement period, the pregnant women were distinguished from the other groups by a different factor of the SCL: at 3-5 months, it was 'Feeling Sick'; at 6-8 months, it was 'Feeling Overweight'; at 9 months, it was 'Feeling Overweight/Physical Stress'; and at postpartum, it was 'Physical Stress'. Also, trend analysis showed a significant tendency for the scores of pregnant women on the SCL 'Negative Emotional State', factor and on the BDI to increase over time, in contrast to those of the other groups.
The primary objectives of this research were to translate, validate, and generate normative data on the SF-36 Health Survey for use among Dutch-speaking residents of the Netherlands. Translation of the SF-36 into Dutch followed the stepwise, iterative procedures developed by the IQOLA Project. Following extensive pilot testing, the SF-36 was administered to: (1) a random sample of adult residents of Amsterdam (n = 4172); (2) a random, nationwide sample of adults (n = 1742); (3) a sample of migraine sufferers (n = 423); and (4) a sample of cancer patients undergoing active anti-neoplastic treatment (n = 485). Data quality across the four studies was consistently high. The rates of missing data ranged from 1% to 5% at the item level, and from 1.2% to 2.6% at the scale level. Multitrait scaling analysis confirmed the hypothesized scale structure of the SF-36 and associated scale scoring in all four samples. Cronbach's alpha coefficients surpassed the 0.70 criterion for group comparisons in all but one case (the Social Functioning scale in the cancer sample), with a mean alpha coefficient across all scales and samples of 0.84. Known-group comparisons yielded consistent support for the validity of the SF-36. In the two community samples, statistically significant differences in SF-36 mean scale scores were observed as a function of age, gender, and the prevalence of chronic health conditions. In the migraine and cancer samples, mean SF-36 scale scores varied significantly as a function of various indicators of disease severity. The SF-36 profiles for the two community samples were highly similar. The cancer sample yielded the lowest SF-36 scores, with the migraine sample holding an intermediate position. On-going studies will generate data on the responsiveness of the SF-36 to within-group changes in health over time. Efforts are underway to translate and validate the questionnaire for use among ethnic minority groups in the Netherlands.
STUDY OBJECTIVES: There is some evidence that magnesium, when infused into asthmatic patients, can produce bronchodilation in addition to that obtained from standard treatments. This systematic review examined the effect of intravenous magnesium sulfate used for patients with acute asthma managed in the emergency department. METHODS: Only randomized controlled trials were eligible for inclusion. Studies were included if patients presented with acute asthma and were treated with intravenous magnesium sulfate versus placebo. Trials were identified from the Cochrane Airways Review Group register, which consists of a combined search of EMBASE, MEDLINE, and CINAHL databases and hand-searching of 20 key respiratory journals. Bibliographies from included studies and known reviews were searched. Primary authors and content experts were contacted. Data were extracted and methodologic quality was assessed independently by 2 reviewers. Missing data were obtained from authors. RESULTS: Seven trials (5 adult, 2 pediatric) involving a total of 668 patients were included. Overall, admission to hospital was not statistically reduced using magnesium sulfate (odds ratio [OR] 0.31, 95% confidence interval [CI] 0.09 to 1.02). In the severe subgroup, admissions were reduced in those receiving magnesium sulfate (OR 0.10, 95% CI 0.04 to 0.27). Overall, patients receiving magnesium sulfate demonstrated nonsignificant improvements in peak expiratory flow rates (PEFR) when all studies were pooled (weighted mean difference [WMD] 29 L/min, 95% CI -3 to 62). In studies of patients with severe acute asthma, PEFR WMD improved by 52 L/min (95% CI 27 to 78) favoring magnesium sulfate treatment. The absolute FEV(1) also improved by 10% predicted (95% CI 4 to 16) in patients with severe acute asthma. No clinically important changes in vital signs or side effects were reported. CONCLUSION: Current evidence does not clearly support routine use of intravenous magnesium sulfate in all patients with acute asthma presenting to the ED. However, magnesium sulfate appears to be safe and beneficial for patients who present with severe acute asthma. Practice guidelines need to be changed to reflect these results.
OBJECTIVE: The aim of this study was to assess the effect of H. pylori eradication on ulcer recurrence in North American duodenal ulcer patients by examining only treatment studies that met rigorous methodologic criteria. METHODS: Data sources were computerized bibliographic searches from 1983, review of reference lists, communication with companies that manufacture medications used for H. pylori therapy in the U.S., and H. pylori investigators, review of open presentations to the Food and Drug Administration, and review of abstracts from annual scientific meetings. Criteria for study inclusion were double blind, randomized North American trials of H. pylori therapy for duodenal ulcer, scheduled endoscopic follow-up exams for > or = 6 months, and H. pylori cure documented > or = 4 wk after completion of therapy by at least two endoscopic biopsy tests. Seven relevant trials were identified. Data were abstracted independently and disagreement was resolved by consensus. We obtained missing data and identified erroneous assessments through contact with an author or sponsor of all studies. RESULTS: The common odds ratio for ulcer recurrence was 0.20 (95% CI, 0.13-0.31) and 2.8 patients would need to be successfully treated to prevent one ulcer recurrence at 6 months. The pooled ulcer recurrence rate at 6 months in patients with H. pylori eradication was 20%. CONCLUSION: Results of North American studies of highest methodological quality confirm that H. pylori eradication markedly decreases ulcer recurrence. Nevertheless, 20% of patients in these studies had ulcer recurrence within 6 months, despite successful cure of infection and no reported use of NSAIDs. Non-H. pylori, non-NSAID ulcers may be more common in the U.S. than previously believed.
An increasing use of non-invasive techniques and arteriographies of the coronary, carotid or femoral arteries has taken place during recent years. This has prompted researchers to perform long-term randomized trials aiming at reducing atherosclerosis progression or achieving regression by cholesterol lowering in high risk populations. These trials are designed to use outcomes such as various indices of atherosclerosis which are assessed repeatedly over time. There are major decisions to be made contingent on the data structures in these trials, such as sphericity, interaction, development over time, missing data, non-normality etc. So, the statistical analysis of such data needs to be planned and specified a priori in a unified manner. This is demonstrated for the Probucol Quantitative Regression Swedish Trial (PQRST) which is designed to answer the question whether the drug probucol, given in combination with diet and cholestyramine, can delay development of atherosclerosis in hypercholesterolemic patients up to 70 years old. Change in atheroma volume is assessed by a newly developed quantitative angiographic technique based on digitized angiograms.
The organization of controlled clinical trials requires well-defined clerical procedures which, with large-scale studies, are so monotonous that it is difficult to attract and keep staff of a sufficiently high calibre. In a large-scale trial of pulmonary tuberculosis, a computer is being used to undertake much of the routine clerical work, including (1) the preparation of an appointments diary, which also specifies the exact requirements for the trial, and (2) the storage of all the data on magnetic tape so that periodic checks can be made for missing data and interim and final analyses can be produced rapidly. These arrangements reduce the time spent by clerical and statistical staff to a minimum. Although a strict evaluation of the effect of introducing the computer has not yet been made, this approach does appear to be sufficiently promising to warrant further investigations of a similar type.
Postmarketing Surveillance (PMS) concerns the investigation of side-effects of drugs after they are introduced into the market. Traditionally, data collection for PMS-studies has been paper-based. The increasing number of general practitioners (GP) that use Computer-Based Patient Records (CBPR) and the central role these general practitioners in the Netherlands play in the delivery of care makes the use of CBPRs as a resource of data for PMS studies possible. Analysis of the current available CBPRs, however, proved them insufficient for PMS studies, because too much data is available only in free text, and other necessary data for PMS is lacking. To make the CBPR suitable for PMS, we had to build a software-module that could be plugged into the computer system of the GP. The module checks the data immediately after they it has been entered into the system, and missing data is requested. Initial filed studies have shown that, with this module, the collection of PMS data is feasible.
Peripheral blood samples were collected from 30 normal male volunteers before and at intervals after inhaling 0.4 ppm ozone for 4 h. Data from 4 of the subjects were excluded from the analysis because of missing data points. The blood samples were cultured for 48 h, slides made and stained with a uniform Giemsa stain, and 100 metaphase spreads per subject per treatment scored for chromosome aberrations. Cells with suspected aberrations were photographed, destained, restained with a banding procedure and rephotographed to identify the specific chromosomes and regions involved. Pre-exposure, immediate post-exposure, 3 days post-exposure, 2 weeks post-exposure and 4 weeks post-exposure means for the percentage of cells with 46 chromosomes were 93.0, 93.6, 91.7, 94.5 and 94.2, respectively; in the same order, the mean number of cells with chromatid and/or chromosome breaks per order, the mean number of cells with chromatid and/or chromosome breaks per 100 cells was 0.96, 0.85, 1.00, 0.88 and 0.81 respectively, and for chromatid and/or chromosome gaps per 100 cells: 1.35, 0.96, 1.35, 0.81 and 0.77, respectively. The means for each of these parameters as well as the mean frequencies of complex aberrations are not statistically significantly different between blood sampling times. The distribution of aberrations by chromosome and light and dark bands is not significantly influenced by ozone exposure. These data indicate no apparent detectable human cytogenetic effect due to exposure to ozone under the conditions of this experiment.
OBJECTIVES: Birth certificates are a major source of population-based data on maternal and perinatal health, but their value depends on the accuracy of the data. This study assesses the validity of information recorded on the birth certificates for women in Washington State who were considered to be low risk at entry into care. METHODS: Birth certificates were matched to data abstracted from prenatal and intrapartum clinic and hospital records of a sample of 1937 Washington State obstetrical patients who were considered to be low risk at the beginning of their pregnancies. Accuracy of a variety of pregnancy characteristics (e.g., complications, procedures) on the birth certificate was analyzed using percentage agreement and sensitivity with record abstracts as the "gold standard." Next, we weighted the data from each source to produce estimates of pregnancy characteristics in the population. We compared these estimates from the two data sources to see whether they provide similar pictures of this subpopulation. RESULTS: Missing data for specific items on the birth certificates ranged from 0% to 24%. The birth certificate accurately captured gravidity and parity, but was less likely to report prenatal and intrapartum complications. The population estimates of the two data sources were significantly different. CONCLUSIONS: Because birth certificates significantly underestimated the complications of pregnancies, number of interventions, number of procedures, and prenatal visits, use of these data for health policy development or resource allocation should be tempered with caution.
The search for truth and its unbiased reporting are ultimate goals of conducting scientific research. Ideally, the reporting of research data ought to be an objective task. In practice, however, it is fraught with numerous statistical and ethical pitfalls, seldom addressed in formal emergency medicine training. The lure of academic celebrity and related influences may persuade researchers to report results in ways that make data appear more interesting, or worthy of publication. Several examples of potentially misleading data reporting are illustrated, including using inappropriate statistical tests, neglecting negative results, omitting missing data points, failing to report actual numbers of eligible subjects, using inappropriate graph labels or terminology, data dredging, and others. Although potentially inaccurate or inflated methods of data reporting may not constitute overt scientific misconduct, the intentional misrepresentation of data is a form of fraud or deception. Publicly funded academic inquiry is a privilege and honor enjoyed by a trusted few. Regardless of outcome, every effort should be made to report data in the most scientifically accurate method. To this end, the Society for Academic Emergency Medicine Code of Conduct and American College of Emergency Physicians Code of Ethics provide important guidance toward the accurate, compassionate, competent, impartial, and honest conduct of scientific research. Accuracy and authenticity in data reporting are first and foremost a matter of individual integrity, and are crucial to the preservation of academic credibility, the protection of future patients, and the public's trust in the medical research enterprise.
BACKGROUND: The association between coronary heart disease and lesions of the coronary arteries has led to investigations of different interventions on atherosclerotic change. Currently, B-mode ultrasound of the peripheral arterial vessels, rather than arteriography of the coronary arteries, provides the most accurate evaluation of atherosclerotic disease extent in the patient. METHODS AND RESULTS: When measuring the effect of risk factor modification on atherosclerotic change, it is important to select appropriate methods and end points for quantifying disease and evaluating subsequent change. Measurements must be valid, precise, and reliable and require appropriate a priori definitions of end points and their change. Consistent methodology within studies is crucial. Multiple measurements and data reduction methods can increase the efficiency of comparisons and merit careful consideration. Missing data arising from nonvisualization of sites complicate analyses. Identifying both covariates of atherosclerotic change and possible confounding interventions require monitoring biochemical, physiological, and/or clinical variables and making inferences from these. CONCLUSIONS: To strengthen the rationale for use of B-mode ultrasonography in assessing the natural history of atherosclerosis, four methodological issues must be addressed: evaluation of primary end points using composite and/or individual measurements of atherosclerotic assessment from the carotid arteries, evaluation of new methodology that may allow assessment of the anatomy of specific lesions and/or their potential for rupture, development of methods making complementary use of both angiographic measurements of lumen diameter and ultrasound assessment of the arterial wall, and concrete demonstration of a direct link between increasing intimal-medial thickness and subsequent clinical events. The use of a continuous variable (intimal-medial thickness) in ultrasound studies offers cost/benefit advantages; this methodology continues to evolve.
The problems of creating and validating medical data are discussed. These difficulties relate to the structuring of data and its definiton. The necessity for clarity of thought, coherence and logic in data collection is stressed. Difficulty in medical and lay staff training shows that this is a continuing problem. Data validation must be the major province of senior as well as junior doctors. It is an absoulte essential continuing process and without valid data most analyses are not worthwhile because of high error rates and/or too much missing data.
Based on the linearity of the Radon transform and the convolution-backprojection reconstruction algorithm, a new linear-vector space notation is introduced that is of general use in computed tomography (CT). Using this notation, a consistency condition for the completion of incomplete projection data is described. This consistency condition leads to singular or ill-conditioned systems of linear equations for the unknown projection data. Using regularization methods, an algorithm for the consistent projection completion is presented that can exploit symmetries of the missing data region. The performance of the new algorithm is documented with simulated and actualy measured CT-projection data. The algorithm quantitatively improves CT reconstructions with realistic amounts of data and noise and can be used for the completion of arbitrary regions of missing projections.