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Results for “Internal validation”

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At least 847 records · Page 47Linked to original sources

PubMed2003

Clinical prediction rule for 30-day mortality in Björk-Shiley convexo-concave valve replacement.

BACKGROUND AND OBJECTIVE: We aimed to develop a clinical prediction rule for 30-day mortality in patients undergoing Björk-Shiley convexo-concave (BScc) valve replacement, based on primary valve implantation procedures. METHODS: We studied 30-day mortality in 2,263 patients who received a BScc valve between 1979 and 1985 in The Netherlands. A logistic regression model was constructed and internally validated with bootstrapping techniques. RESULTS: Predictors for mortality were emergency operation, coronary artery disease, mitral or double-valve replacement, BScc implant being a reoperation, endocarditis, poor left ventricular function, age, concomitant tricuspid valve plasty, and aortic root replacement. The area under the receiver operating characteristic curve (AUC) for the predicted probability of death was 0.76 (95% CI 0.72-0.80). The model calibrated well, and had adequate discriminative ability in 195 BScc valve patients who underwent explantation, including 53 prophylactic explantations (AUC 0.81, 95% CI 0.73-0.89). CONCLUSION: A prediction rule derived from BScc valve implantation data performed well in patients undergoing explantation. Because the model provides accurate individualized estimates of the risk of mortality after reoperation, it may be helpful for decision making in patients with BScc valves.

Adult↗

PubMed1998

Prediction of relapse within eight weeks after an acute asthma exacerbation in adults.

Associations between historical, presenting, and treatment-related characteristics and relapse within 8 weeks after a moderate to severe asthma exacerbation were studied in a cohort of 284 adult asthmatics. Data were collected prospectively, and a multivariate model was developed and internally validated. Within 10 days, only 8% had relapsed, increasing to 45% by 8 weeks. Three variables that could be identified at the time of discharge were independently associated with relapse. These included: having made three or more visits to an emergency department in the prior 6 months (hazard ratio (HR) = 2.3, 95% CI = 1.6-3.4); difficulty performing work or activities as a result of physical health in the 4 weeks prior (HR = 2.7, 95% CI = 1.6-4.3); discontinuing hospital-based treatment for the exacerbation within 24 hours without having achieved a peak expiratory flow rate of at least 50% of predicted (HR = 2.6, 95% CI = 1.6-4.1). These risk factors may help to identify patients with poorly controlled asthma in need of more intensive and comprehensive management.

Acute Disease↗

PubMed1999

Quantifying excess length of postoperative stay attributable to infections: a comparison of methods.

To quantify the net effect of deep surgical site infection (DSSI) on postoperative stay (POS) among patients who had undergone open heart surgery, and to assess the comparability of two methods, two observational studies were conducted: one on a retrospective cohort of 701 operated patients, and the other on a cohort of 31 infected patients versus a cohort of uninfected patients, with 1:1 matching. In addition to DSSI, a further three factors were identified by multivariate analysis as independent POS-related predictor variables. After internal validation of the multivariate model, excess POS attributable to DSSI amounted to 20.7 days (95% confidence interval [CI] 16.7-24.9). In contrast, excess length of stay attributable to DSSI among the matched pairs who survived infection (22) totaled 14.3 days (95% CI 3.2-25.4) and 26.5 days (mean and median differences). Multivariate techniques may prove a more appropriate and reliable analysis than matched-pair comparisons for the purpose of evaluating the extra stay and cost attributable to the nosocomial infections.

Adolescent↗

PubMed2000

Why use placebos in clinical trials? A narrative review of the methodological literature.

Researchers have a number of different options for their choice of control or comparison intervention in randomized trials. We surveyed the methodological literature looking for reasons why a researcher might choose to administer a placebo (i.e., a mimic intervention) to control subjects. Two implicit assumptions were that the issue of placebo is pertinent only to drug trials and that the nonplacebo effect of a treatment is the "real" or "true" effect. Explicit reasons given in the literature for the use of placebos were facilitating blinding and controlling for the placebo effect. The importance of the latter was often inadequately argued. Reasons to avoid placebos in controlled trials, other than ethics and feasibility, are that placebos do not inform real decisions, and may interfere with accurate estimation of effect size and with nonspecific aspects of treatment. Placebo-controlled trials have high internal validity but may be difficult to apply to clinical practice; the situation is reversed for trials without placebo control.

Double-Blind Method↗

PubMed2001

Scopolamine nasal spray in motion sickness: a randomised, controlled, and crossover study for the comparison of two scopolamine nasal sprays with oral dimenhydrinate and placebo.

Scopolamine has been used successfully for treatment of motion sickness for almost a century and the nasal administration was first studied 50 years ago. However, there never appeared a nasal dosage form. Finally, after finding a stable and suitable formulation for scopolamine, a study to investigate efficacy, safety, and tolerability was conducted, with a randomised, double-blind, double-dummy, crossover, Latin square design including placebo control and a placebo/placebo control for internal validity at the German Air Force Institute of Aviation Medicine. To assess the efficacy of a new, stable and well-tolerated formulation of scopolamine nasal spray the reproducible induction of whole body vibrations by a rotating chair was chosen and a validated seasickness score (SKS). The reduction of SKS showed that scopolamine nasal spray at a concentration of 0.2% was statistically superior to both placebo and dimenhydrinate (P=0.003 and 0.004, respectively). There were no signs for a nasal or epipharyngeal irritation of the mucous membrane. Scopolamine nasal spray was found to be an effective and safe treatment in motion sickness, with a fast onset of action within 30 min after administration.

Administration, Inhalation↗

PubMed2001

Development of an EORTC disease-specific quality of life module for use in patients with gastric cancer.

Quality of life (QL) is an important outcome in clinical trials in oncology. There is currently no valid international QL measure for gastric cancer. This paper describes the development of a QL module for gastric cancer to supplement the European Organization for Research and Treatment of Cancer (EORTC) Quality of life (QLQ-C30) questionnaire. Phases I to III of module development were conducted in the United Kingdom, France, Germany and Spain according to EORTC QL Group guidelines. Twenty relevant QL issues were generated from the literature and interviews with health professionals (n=24) and patients (n=58). This produced a 24 item provisional module. Further testing in 115 patients resulted in the QLQ-STO22, containing 22 questions, conceptualised into five scales and four single items, related to disease symptoms, treatment side-effects and emotional issues specific to gastric cancer. The use of the QLQ-C30 supplemented by the QLQ-STO22 will provide a comprehensive QL measure for international trials in gastric cancer.

Adult↗

PubMed1996

Effectiveness of antiepileptic prophylaxis used with supratentorial craniotomies: a meta-analysis.

Thirty publications on the effectiveness of prophylactic antiepileptic drugs (AEDs) with supratentorial craniotomies were reviewed (1980-1995). After a first selection, six controlled studies remained (11 publications). These six were evaluated according to previously defined methodological criteria. The criteria were divided into three main categories: (1) internal validity, (2) proper and relevant outcome-measures and (3) analysis. In this way a maximum of 145 points could be obtained for each study. Three studies were considered to be of satisfactory methodological quality (> or = 55% or 145 points) and the odds ratios were calculated as a measure of association between treatment and occurrence of convulsions. The odds ratios of these three studies were statistically pooled using the Mantel-Haenszel Estimator. From this test it appeared that prophylactically used AEDs showed a tendency to prevent postoperative convulsions, but this effect was certainly not statistically significant (P = 0.1 one-tailed). Points of attention concerning possible future investigations are stressed.

Brain Diseases↗

PubMed1997

Designing research: ex post facto designs.

The research design is the overall plan or structure of the study. The goal of a good research design is to insure internal validity and answer the question being asked. The only clear rule in selecting a design is that the question dictates the design. Over the next few issues this column will cover types of research designs and their inherent strengths and weaknesses. This article discusses ex post facto research.

Choice Behavior↗

PubMedDate not supplied

Development and testing of the Clinical Post-Conference Learning Environment Survey.

Clinical postconference is an integral component of the required laboratory hours in undergraduate baccalaureate nursing education. Empirical evidence supporting the educational benefits of this activity are nearly nonexistent. This article describes the development and psychometric testing of a self-report instrument designed to measure clinical postconference learning environments as perceived by undergraduate nursing students and faculty. The Clinical Post-Conference Learning Environment Survey (CPCLES) consists of 54 items and has been tested with more than 500 participants in three schools of nursing in the Midwest. Based on theoretical support and comprehensive review of the literature, six components of the learning environment are measured in two forms of the instrument; an actual scale and an importance scale. Content validity, internal consistency, and test-retest reliability are discussed. Using the CPCLES, perceptions of undergraduate nursing students and faculty were measured. Significant differences between the actual components of the learning environment and the correlated ratings of the importance of these components were found. Faculty perceived a significantly greater amount of teacher support, task orientation, and innovation in the postconference learning environment than did undergraduate students. No differences were noted between faculty and students regarding the importance of the learning environment components. This study presents findings with the use of the first instrument developed to measure clinical postconference learning environments. The congruence and discrepancy among and between learning groups' perceptions carry implications for educational practices in this setting. Subseqent investigations using this tool may be able to link the perceived learning environment to valued cognitive, affective, and behavioral learning outcomes.

Adult↗

PubMed2006

Methods of defining best practice for population health approaches with obesity prevention as an example.

Childhood obesity has reached a crisis stage and has become a population health issue. The few traditional systematic reviews that have been done to identify best practice provide little direction for action. The concept of evidence-based practice has been adopted in health care, and in medicine in particular, to determine best practice. Evidence-based medicine has its origins in the scientific method and for many researchers this concept means strict adherence to standards determining internal validity in order to justify a practice as evidence based. Practitioners addressing population health face challenges in identifying criteria for determining evidence, in part because of the nature of population health with its goal of shifting the health of whole populations. As well, the type of evidence provided by more traditional critical appraisal schema is limiting. Expanded approaches in finding and defining evidence have been proposed that use: expert panels; broad and inclusive search and selection strategies; appraisal criteria that incorporate context and generalizability. A recent synthesis of 147 programmes addressing childhood overweight and obesity provides a concrete example of using a broader approach to identify evidence for best practice (Flynn et al. 2006). Incorporating evaluation and population health frameworks as criterion components in addition to traditional methodological rigour criteria, this synthesis has identified programmes that provide contextual information that can be used to populate what Swinburn et al. (2005) have described as the 'promise table'. Using this approach a range in 'certainty of effectiveness' and a range in 'potential for population impact' are integrated to identify promising strategies. The exercise can provide direction for agencies and practitioners in taking action to address obesity.

Adolescent↗

PubMed1987

Isolation and characterization of a nuclear depressive syndrome.

We investigated the nosology of endogenous depression by numerical taxonomy. Five hundred and sixty-nine patients diagnosed as having unipolar major depressive disorder in the NIMH Clinical Research Branch Program on the Psychobiology of Depression-Clinical were studied. Thirty-six symptoms which might distinguish endogenous from non-endogenous depressions were chosen from the literature. Patients' symptom profiles assessed by structured interview were grouped by two methods: a K-means improvement of Ward's method of cluster analysis, and a latent class algorithm. The methods produced very similar groups and several internal validity criteria suggested that the groups were not spurious. Cluster 1, 'nuclear depression,' included a nucleus of patients common to multiple definitions of endogenous depression. The non-nuclear group scored as less neurotic than the nuclear group on personality tests administered during the index episode. The groups do not differ in frequency, number or severity of reported life events prior to onset of the index episode. The nuclear group shows a poor prognosis on two-year prospective follow-up, greater disturbance on personality inventories, and increased heritability of depression in siblings.

Adult↗

PubMed2005

A multidimensional differential proteomic platform using dual-phase ion-exchange chromatography-polyacrylamide gel electrophoresis/reversed-phase liquid chromatography tandem mass spectrometry.

Differential proteomic analysis has arisen as a large-scale means to discern proteome-wide changes upon treatment, injury, or disease. Tandem protein separation methods are required for large-scale differential proteomic analysis. Here, a novel multidimensional platform for resolving and differentially analyzing complex biological samples is presented. The platform, collectively termed CAX-PAGE/RPLC-MSMS, combines biphasic ion-exchange chromatography with polyacrylamide gel electrophoresis for protein separation, quantification, and differential band targeting, followed by capillary reversed-phase liquid chromatography and data-dependent tandem mass spectrometry for quantitative and qualitative peptide analysis. CAX-PAGE provides high protein resolving power with a theoretical peak capacity of 3570, extendable to 7600, a wide protein mass range verified from 16 to 273 kDa, and reproducible differential sample comparison without the added expense of fluorescent dyes and imaging equipment. Demonstrated using a neuroproteomic model, CAX-PAGE revealed an increased number of differential proteins, 137, compared with 82 found by 2D difference gel electrophoresis. When combined with RPLC-MSMS for protein identification, an additional quantification step is performed for internal validation, confirming a 2-fold or greater change in 89% of identified differential targets.

Animals↗

PubMed2002

Solution structure of a monoheme ferrocytochrome c from Shewanella putrefaciens and structural analysis of sequence-similar proteins: functional implications.

Within the frame of the characterization of the structure and function of cytochromes c, an 81-amino acid cytochrome c was identified in the genome of Shewanella putrefaciens. Because of the scarce information about bacterial cytochromes of this type and the large variability in sequences and possibly function, we decided to proceed to its structural characterization. This protein was expressed in Escherichia coli and purified. The oxidized species is largely high spin, with a detached methionine, whereas the reduced species has the classical His/Met axial ligation to iron. The NMR solution structure of the reduced form was determined on a (15)N-labeled sample, for which 99% of all non-proline backbone (1)H and (15)N resonances have been assigned. One thousand three hundred two meaningful NOEs, out of 1775 NOEs, together with 66 dihedral angles provide a structure with rmsd values from the mean of 0.50 and 0.96 A for backbone and all heavy atoms, respectively. A search of gene banks allowed us to locate 10 different cytochromes c, the sequences of which are more than 30% identical to that of the S. putrefacienscytochrome. For two of them, the structures are known. The structures of the others have been modeled by using the available templates and internally validated. Structural similarities in terms of surface properties account for their biophysical features and provide hints about the function.

Amino Acid Sequence↗

PubMedDate not supplied

Use of robust classification techniques for the prediction of human cytochrome P450 2D6 inhibition.

A new in silico model is developed to predict cytochrome P450 2D6 inhibition from 2D chemical structure. Using a diverse training set of 100 compounds with published inhibition constants, an ensemble approach to recursive partitioning is applied to create a large number of classification trees, each of which yields a yes/no prediction about inhibition for a given compound. These binary classifications are combined to provide an overall prediction, which answers the yes/no question about inhibition and provides a measure of confidence about that prediction. Compared to single-tree models, the ensemble approach is less sensitive to noise in the experimental data as well as to changes in the training set. Internal validation tests indicated an overall classification accuracy of 75%, whereas predictions applied to an external set of 51 compounds yielded 80% accuracy, with all inhibitors correctly identified. The speed and 2D nature of this model make it appropriate for high-throughput processing of large chemical libraries, and the confidence level provides a continuous scale on which to prioritize compounds.

Computer-Aided Design↗

PubMed2003

Virgin olive oil quality classification combining neural network and MOS sensors.

A model based on neural networks has been designed to detect lampante virgin olive oils, a category of olive oil that cannot be consumed without a previous refining process according to the current regulation of the European Communities. The response of 7 metal oxide sensors analyzing 114 olive oil samples has been used in the design, training, and internal validation of the neural network with only 4.5% error in validation. The designed mathematical model, the equations of which are fully described, has been validated also with an external set of 13 samples of diverse varieties and geographical origins with 100% correct classification.

Chemistry Techniques, Analytical↗

PubMed2003

Computational studies of chiral catalysts: a comparative molecular field analysis of an asymmetric Diels-Alder reaction with catalysts containing bisoxazoline or phosphinooxazoline ligands.

A QSAR using Comparative Molecular Field Analysis (CoMFA) is developed for a set of 23 catalysts containing bisoxazoline or phosphinooxazoline ligands that are known to induce asymmetry during the Diels-Alder reaction of N-2-alkenoyl-1,3-oxazolidine-2-one with cyclopentadiene. It is shown that extremely high q(2) statistics can be derived by using standard modeling protocols when internal validation alone is done as well as when an external test set is used. From these models it is shown that approximately 70% of the variance in the observed enantiomeric excess can be attributed to the steric field and the remainder of the variance to the electrostatic field. Suggestions about how to improve the performance of inefficient catalysts are given.

Journal Article↗

PubMed2000

The value of interrupted time-series experiments for community intervention research.

Greater use of interrupted time-series experiments is advocated for community intervention research. Time-series designs enable the development of knowledge about the effects of community interventions and policies in circumstances in which randomized controlled trials are too expensive, premature, or simply impractical. The multiple baseline time-series design typically involves two or more communities that are repeatedly assessed, with the intervention introduced into one community at a time. It is particularly well suited to initial evaluations of community interventions and the refinement of those interventions. This paper describes the main features of multiple baseline designs and related repeated-measures time-series experiments, discusses the threats to internal validity in multiple baseline designs, and outlines techniques for statistical analyses of time-series data. Examples are given of the use of multiple baseline designs in evaluating community interventions and policy changes.

Community Health Services↗

PubMed2001

Efficient screening of covariates in population models using Wald's approximation to the likelihood ratio test.

We propose an efficient algorithm for screening covariates in population model building using Wald's approximation to the likelihood ratio test (LRT) statistic in conjunction with Schwarz's Bayesian criterion. The algorithm can be applied to a full model fit of k covariate parameters to calculate the approximate LRT for all 2k - 1 possible restricted models. The algorithm's efficiency also permits internal validation of the model selection process via bootstrap methods. We illustrate the use of this algorithm for both model selection and validation with data from a Daypro pediatric study. The algorithm is easily implemented using standard statistical software such as SAS/IML and S-Plus. A SAS/IML macro to perform the algorithm is provided.

Adult↗