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At least 271 records · Page 15Linked to original sources
PubMed1998

Molecular phylogeny of the genus Hypochaeris using internal transcribed spacers of nuclear rDNA: inference for chromosomal evolution.

Sequences of the internal transcribed spacers (ITSs) of 18S-26S nuclear ribosomal DNA were used to resolve phylogenetic relationships and chromosomal evolution among 14 species of the genus Hypochaeris (Asteraceae). Parsimony analysis was performed for phylogenetic reconstruction, and sequence divergence between species was estimated. Pairwise sequence divergence within Hypochaeris genus ranged from 0% to 25.68% in ITS1 and from 0% to 17.08% in ITS2. A highly resolved strict-consensus tree was obtained that showed the phylogenetically useful information of ITS sequences within the genus Hypochaeris. Four clades could be well distinguished, one of them formed by the single species H. robertia, which appeared to be the most related to the ancestral species of the genus. The results agree with taxonomic classification based on morphological data, and the tree obtained, when indels are coded as missing data, aggregates the species having the same chromosome number, except in one clade. According to the ITS phylogenetic tree, the chromosomal evolution within the genus Hypochaeris conflicts with the previous hypothesis and suggests that karyotype evolution in Hypochaeris was accompanied with both decreasing and increasing dysploidy, probably with several chromosomal rearrangements, and from an ancestral basic chromosome number of 4 or 5.

Asteraceae↗
PubMed1995

The feasibility and cost of a large multicentre audit of process and outcome of prostatectomy.

Objective--To determine the feasibility of performing multicentre process and outcome audits of common interventions taking prostatic procedures as an example. Design--Prospective, cohort study. Setting--All National Health Service and independent hospitals in Northern, Wessex, Mersey, and South West Thames health regions. Patients--5361 men undergoing prostatectomy identified by 103 of the 107 urologists and general surgeons performing prostatectomy in the study regions. Main measures-- Rates of participation by surgeons and patients; completeness of clinical data provided by surgeons; patient response rate and completeness of patient derived data; and cost. Results--Most surgeons (103,96%) agreed to participate. Overall, the proportion of eligible patients invited to take part was high (89%), although this was only measured in South West Thames, where dedicated data collectors were employed. Few men (80, 1.5%) declined to participate. Of those surviving for three months after surgery, 82.4% (4226) completed and returned the postal questionnaire. The response rate was higher in South West Thames (86.7%) than in the other regions (80.6%-80.8%). The audit was well received: 91% of patients found the questionnaire easy to complete and only 2.3% of them disapproved. Completeness of data was high with both the hospital and patient questionnaires. Missing data occurred in less than 5% of responses to most questions. The attributable cost was 34.50 pounds per patient identified or 44 pounds for patients in whom either the treatment outcome or vital status was known three months after their prostatectomy. Conclusions--This multicentre audit of process and outcome of prostatectomy proved feasible in terms of surgeon participation, patient identification, and the quantity and quality of data collection. Whether the cost was warranted will depend on how surgeons use the audit data to modify their practice.

Aged↗
PubMed1997

Now you see it, now you don't: a comparison of traditional versus random-effects regression models in the analysis of longitudinal follow-up data from a clinical trial.

To illustrate the limitations of commonly used methods of handling missing data when using traditional analysis of variance (ANOVA) models and highlight the relative advantages of random-effects regression models, multiple analytic strategies were applied to follow-up data from a clinical trial. Traditional ANOVA and random-effects models produced similar results when underlying assumptions were met and data were complete. However, analyses based on subsamples, to which investigators would have been limited with traditional models, would have led to different conclusions about treatment effects over time than analyses based on intention-to-treat samples using random-effects regression models. These findings underscore the advantages of models that use all data collected and the importance of complete data collection to minimize sample bias.

Adult↗
PubMed1998

Magnetic resonance imaging for the investigation of knee injuries: an investigation of preferences.

The conventional approach to the diagnosis and treatment of severe knee injuries is arthroscopy, a minimally invasive surgical procedure. Since arthroscopy is an invasive technique that carries risks, magnetic resonance imaging (MRI) is increasingly being used for diagnosis. MRI is potentially associated with diagnostic and therapeutic 'impacts', in that arthroscopy can be avoided. This paper reports a discrete choice conjoint analysis exercise that assessed the value placed on such 'impacts' by potential patients and investigated the degree to which respondents were willing to trade between process and outcome. The marginal rates of substitution between attributes were estimated. The results suggest that the diagnostic and therapeutic 'impacts' of MRI were valued by many respondents. The study has highlighted a number of important issues for the design and analysis of future health-related conjoint studies, including the use of treatment cost as an attribute, dealing with data from lexicographic respondents, and distinguishing between points of indifference and missing data.

Adult↗
PubMedDate not supplied

"Keyhole" method for accelerating imaging of contrast agent uptake.

Magnetic resonance (MR) imaging methods with good spatial and contrast resolution are often too slow to follow the uptake of contrast agents with the desired temporal resolution. Imaging can be accelerated by skipping the acquisition of data normally taken with strong phase-encoding gradients, restricting acquisition to weak-gradient data only. If the usual procedure of substituting zeroes for the missing data is followed, blurring results. Substituting instead reference data taken before or well after contrast agent injection reduces this problem. Volunteer and patient images obtained by using such reference data show that imaging can be usefully accelerated severalfold. Cortical and medullary regions of interest and whole kidney regions were studied, and both gradient- and spin-echo images are shown. The method is believed to be compatible with other acceleration methods such as half-Fourier reconstruction and reading of more than one line of k space per excitation.

Contrast Media↗
PubMed1994

Crossover designs for clinical trials.

I discuss three-period crossover designs for an efficient comparison of two test treatments with special application to clinical trials which often have many practical limitations. In this paper I specify a subset of three-period crossover designs so that the investigators are not left with the problematic two-period two-sequence design, should the trials be terminated after the second period. I show that there is a dramatic reduction in variability for estimating the direct and residual treatment effects in three-period designs compared to two-period designs. I also show that the universally optimal design with ABB and BAA sequences is unsuitable when a complex form of residual effects is suspected, such as the second-order residual effects or treatment by period interactions. The design with ABB, BAA, AAB, and BBA sequences is relatively robust to these uncertain model assumptions. I also discuss missing data problems and conclude that, even with a large proportion of missing values, the three-period design is far more efficient than the two-period design.

Analysis of Variance↗
PubMed1994

A PC program for classification into one of several groups on the basis of longitudinal data.

A stand-alone, menu-driven PC program, ZCLASS, written in GAUSS386i, for classifying subjects into one of several distinct, existing groups on the basis of longitudinal data is described, illustrated, and made available to interested readers. The program accepts data from studies where common times of measurement are planned, but missing data are accommodated in that one or more measurement sequences may be incomplete.

Anthropometry↗
PubMed1988

Microcomputer application of Bayesean probability testing for the identification of bacteria.

A computer program (BACTID) is described which facilitates the identification of bacteria based on a priori data and Bayesean probability testing. The program is not limited to a specific format, has a short execution time, can be easily applied to a variety of situations, and can be run on almost any microcomputer system operating under either 8-bit CP/M or 16-bit MS-DOS/PC-DOS. Additionally, BACTID (1) is not limited to one type of computer (hardware independent), (2) is not limited by size of the computer's random access (RAM independent), (3) can recognize various data bases matrices (format independent), (4) is able to compensate for missing data and (5) allows for various methods of data entry. The efficacy of the program was checked against a commercially available test system and a 99.34% agreement was obtained. Also, the execution time for a 46 x 21 element data matrix was as little as 3.5 s. These results show that microcomputer identification programs are not only viable alternatives to code book registers, but also offer flexibility which is not found in commercial systems.

Bacteria↗
PubMed1989

A comparison of response rate, data quality, and cost in the collection of data on sexual history and personal behaviors. Mail survey approaches and in-person interview.

The authors examined differences in rate of response, data quality, and cost between mail approaches and in-person interview in the collection of data on sexual history and personal behaviors. A sample of women from a midwestern United States university (n = 342) was identified from health service medical records as having been seen for a sexually transmitted disease (cases) or a contraceptive visit (controls) during the latter half of 1985. The women were randomly assigned to one of three data collection strategies. A total of 268 subjects (78%) participated. Results indicated no differences in validity by method of data collection or by case-control status but there were significant differences in completeness, cost, and response rates. In-person interviews resulted in more complete data than mail approaches, although all instruments had low proportions of missing data (0.001-0.006). Response rate differences were not found when data collection methodologies were compared (75-82%) but were found in case-control analyses. Cases were consistently less likely to participate and significantly less likely to respond by mail (p less than 0.05). The cost of the in-person interview was approximately four times that of the mail survey for the data collection. Implications of the case-control response rate difference suggest that mail methodologies, although low in cost, may introduce sampling bias in studies of sexually transmitted diseases.

Adolescent↗
PubMed1993

Maximum a posteriori estimation with Good's roughness for three-dimensional optical-sectioning microscopy.

The three-dimensional image-reconstruction problem solved here for optical-sectioning microscopy is to estimate the fluorescence intensity lambda(x), where x epsilon R3, given a series of Poisson counting process measurements [Mj(dx)]jJ = 1, each with intensity [formula: see text] with [formula: see text] being the point spread of the optics focused to the jth plane and sj(y) the detection probability for detector point y at focal depth j. A maximum a posteriori reconstruction generated by inducing a prior distribution on the space of images via Good's three-dimensional rotationally invariant roughness penalty [formula: see text] It is proven that the sequence of iterates that is generated by using the expectation maximization algorithm is monotonically increasing in posterior probability, with stable points of the iteration satisfying the necessary maximizer conditions of the maximum a posteriori solution. The algorithms were implemented on the DECmpp-SX, a 64 x 64 parallel processor, running at < 2 s/(64(3), 3-D iteration). Results are demonstrated from simulated as well as amoebae and volvox data. We study performance comparisons of the algorithms for the missing-data problems corresponding to fast data collection for rapid motion studies in which every other focal plane is removed and for imaging with limited detector areas and efficiency.

Algorithms↗
PubMed1980

Studies on occupational health: a critique.

A critique of 48 recent articles dealing with occupational health was undertaken by two readers using a set of questions devised to assess adherence to selected methodologic principles concerning data quality. Articles were read independently, responses to assessment questions were discussed and differences between readers reconciled. The greatest inattention to principles was found in the areas of sample size; definition of exposure; description, standardization, and validation of data sources; use of "blind" observers; and the possible effect of missing data on the results. Rigorus attention to these methodologic principles is necessary if the results of studies are to be accepted and applied in the prevention and control of occupational hazards.

Occupational Medicine↗
PubMed1996

[Treatment of convulsions in newborn infants].

OBJECTIVE: Measurement of incidence of neonatal seizures and evaluation of the therapeutic strategy used. SETTING: Neonatal intensive care unit, University Hospital, Groningen, the Netherlands. DESIGN: Retrospective, descriptive. METHODS: All patients admitted in a period of 5.5 years who had clinical seizures within 28 days from birth received pharmacological treatment in 4 steps. When a seizure remained clinically uncontrolled, the next step was taken. Step 1: methylphenobarbital 15-35 mg/kg i.v. Step 2: phenytoin 15-35 mg/kg i.v. After an initial loading dose of 15 mg/kg i.v., both the methylphenobarbital and the phenytoin loading dose were stepwise increased until reaching the maximum of 35 mg/kg. Step 3: clonazepam 1-2 x 0,15 mg/kg i.v. Step 4: thiopental 1-2 mg/kg/hour i.v. RESULTS: The incidence of neonatal seizures was 121/2068 (5.9%). For assessment of the efficacy of the therapeutic strategy used, data of 37 patients were not available: 16 patients because of missing data, 11 because of deviation from the strategy and 10 because they died during the strategy. Cases of 84 patients could be evaluated for treatment response. The cumulative response rates were 68% (57/84) controlled seizures for methylphenobarbital, 87% (73/84) for phenytoin, 94% (79/84) for clonazepam, and 96% (81/84) for thiopental. For both methylphenobarbital and phenytoin a marked increase in clinical response was seen at increasing loading doses. CONCLUSION: The stepwise therapeutic strategy used in this study proved to be successful in most cases of neonatal seizures. The anticonvulsive action of both methylphenobarbital and phenytoin appeared to be dose-related.

Anticonvulsants↗
PubMed1992

A method for assessing patterns of familial resemblance in complex human pedigrees, with an application to the nevus-count data in Utah kindreds.

An analytic method is described for estimating phenotypic correlations between pairs of members of specific relationships in pedigrees. In estimating correlations, this new method allows simultaneous adjustment for available covariates such as age, gender, environmental factors, and variables reflecting ascertainment mode, through mean- and variance-regression models. The estimated correlations and regression coefficients corresponding to covariates are consistent and asymptotically normally distributed. Differing from a full-likelihood approach, this new method does not require the assumption of a particular joint distribution of phenotypes from a pedigree, such as the multivariate normal distribution, but instead only requires correct specification of mean- and variance-regression models. Within this framework, missing data, if they are missing completely at random, can be ignored without biasing estimates. The method is illustrated by an application using nevus-count data from 28 Utah kinships. The results from the analysis are that covariate-adjusted nevus counts are correlated between parents and children (correlation .22; P less than .001) and between siblings (correlation .32; P less than .001), while the correlation of -.04 between husband and wife is not significantly different (P = .31) from 0. This result is consistent with a genetic etiology of nevus count.

Dysplastic Nevus Syndrome↗
PubMed1992

Closed-form estimates for missing counts in two-way contingency tables.

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.

Algorithms↗
PubMed2000

Antibiotics for preterm labour with intact membranes.

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.

Anti-Bacterial Agents↗
PubMed2000

Magnesium sulfate for treating exacerbations of acute asthma in the emergency department.

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.

Acute Disease↗
PubMedDate not supplied

The use of lung function tests in identifying factors that affect lung growth and aging.

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.

Adolescent↗
PubMed1996

Guidelines for reporting results of quality of life assessments in clinical trials.

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.

Clinical Trials as Topic↗