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Results for “External validity”

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At least 937 records · Page 52Linked to original sources
PubMed2003

Muscle strength testing: evaluation of tests of explosive force production.

The purpose of the study was to evaluate four tests of explosive force production (EFP). Specifically, the main aims of the study were to assess the reliability of different EFP tests, to examine their relationship with maximum muscle strength, and to explore the relationship between EFP tests and functional movement performance. After an extensive preliminary familiarization with the tasks, subjects ( n=26) were tested on maximum explosive strength of the elbow extensor and flexor muscle, as well as on rapid elbow extension and flexion movements performed in both an oscillatory and a discrete fashion. In addition to maximum force ( F(max)), four different EFP tests were assessed from the recorded force-time curves: the time interval elapsed between achieving 30% and 70% of F(max) ( F(30-70%)), the maximum rate of force development (RFD), the same value normalized with respect to F(max) (RFD/ F(max)), and the force exerted 100 ms after the contraction initiation ( F(100 ms)). Excluding F(30--70%), all remaining EFP tests revealed either good or fair reliability (intraclass correlation coefficients being within 0.8-1 and 0.6-0.8 intervals, respectively) which was also comparable with the reliability of F(max). RFD and F(100 ms) demonstrated a positive relationship with F(max), but not T(30-70%) and RFD/ F(max). Stronger elbow flexor muscles also demonstrated higher values of RFD and F(100 ms) than weaker elbow extensor muscles, while no difference was observed between either T(30-70%) or RFD/ F(max) recorded from two muscles. Despite the simplicity of the tested movement tasks, the relationship observed between the EFP tests and the peak movement velocity remained moderate and partly insignificant. It was concluded that most of the EFP tests could be reliable for assessing neuromuscular function in their muscle-force- (or, indirectly, muscle size) dependent (such as RFD and F(100 ms)), or muscle-force-independent ( T(30-70%) and RFD/ F(max)) forms. However, their "external validity" when applied to assess the ability to perform rapid movements could be questioned.

Adult↗
PubMed2004

Heat requirement for the onset of the Olea europaea L. pollen season in several sites in Andalusia and the effect of the expected future climate change.

Olives are one of the largest crops in the Mediterranean region, especially in Andalusia, in southern Spain. A thermal model has been developed for forecasting the start of the olive tree pollen season at five localities in Andalusia: Cordoba, Priego, Jaen, Granada and Malaga using airborne pollen and meteorological data from 1982 to 2001. Threshold temperatures varied between 5 degrees C and 12.5 degrees C depending on bio-geographical characteristics. The external validity of the results was tested using the data for the year 2002 as an independent variable and it confirmed the model's accuracy with only a few days difference from predicted values. All the localities had increasingly earlier start dates during the study period. This could confirm that olive flower phenology can be considered as a sensitive indicator of the effects of climate fluctuations in the Mediterranean area. The theoretical impact of the predicted climatic warming on the olive's flowering phenology at the end of the century is also proposed by applying Regional Climate Model data. A general advance, from 1 to 3 weeks could be expected, although this advance will be more pronounced in mid-altitude inland areas.

Climate↗
PubMed2005

[Toxoplasmosis round-robin test in Austria: results and limits of the toxoplasmosis screening].

In 1983 the Osterreichische Gesellschaft für Qualitätssicherung und Standardisierung medizinisch-diagnostischer Untersuchungen (OQUASTA) has invited the Department of Medical Parasitology of the Clinical Institute of Hygiene and Medical Microbiology, University of Vienna (today: Medical University of Vienna), to establish an external quality assessment service on the detection of specific antibodies against Toxoplasma gondii, one of the most prevalent protozoic parasites in the world. The objective of this project was the support of Austrian laboratories in standardising their test methods for the detection of specific antibodies against T. gondii. Between 1983 and 2004, 45 collaborating studies were carried out. During this period, the number of participating laboratories has increased from 10 in 1983 to about 50 in recent years. In total, the test results produced by the laboratories matched with the nominal values in more than 90%. On the examples of three human cases we demonstrate that externally validated serological methods alone, despite their great benefit, are not enough for a sufficient serodiagnosis of toxoplasmosis; unusually complicated serological situations do arise and can only be met by the knowledge about special tests, the application of an appropriate examination strategy and -- last but not least -- by many years of experience.

Austria↗
PubMed2005

The rationale for a spine registry.

In the discussion about the rationale for spine registries, two basic questions have to be answered. The first one deals with the value of orthopaedic registries per se, considering them as observational studies and comparing the evidence they generate with that of randomised controlled trials. The second question asks if the need for registries in spine surgery is similar to that in the arthroplasty sector. The widely held view that randomised controlled trials are the 'gold standard' for evaluation and that observational methods have little or no value ignores the limitations of randomised trials. They may prove unnecessary, inappropriate, impossible, or inadequate. In addition, the external validity and hence the ability to make generalisations about the results of randomised trials is often low. Therefore, the false conflict between those who advocate randomised trials in all situations and those who believe observational data provide sufficient evidence needs to be replaced with mutual recognition of their complementary roles. The fact that many surgical techniques or technologies were introduced into the field of spine surgery without randomised trials or prospective cohort comparisons makes obvious an even increased need for spine registries compared to joint arthroplasty. An essential methodological prerequisite for a registry is a common terminology for reporting results and a sophisticated technology that networks all participants so that one central data pool is created and accessed. Recognising this need, the Spine Society of Europe has researched and developed Spine Tango, the first European spine registry, which can be accessed under www.eurospine.org.

Arthroplasty↗
PubMed2005

Back related outcome assessment instruments.

A literature review of the most widely used condition specific, self administered assessment questionnaires for low back pain had been undertaken. General and historic aspects, reliability, responsiveness and minimum clinically important difference, external validity, floor and ceiling effects, and available languages were analysed. These criteria, however, are only part of the consideration. Of similar importance are the content, wording of questions and answers in each of the six questionnaires and an analysis of the different score results. The issue of score bias is discussed and suggestions are given in order to increase the construct validity in the practical use of the individual questionnaires.

Disability Evaluation↗
PubMed2002

Cross-cultural assessment of childhood temperament. A confirmatory factor analysis of the French Emotionality Activity and Sociability (EAS) questionnaire.

The Emotionality Activity Sociability (EAS) questionnaire focuses on heritable individual differences in reactivity and behavior which are often referred to in developmental temperament research. Psychometric properties of the French version of EAS were examined in a sample of 197 school-children aged six to 12 years. Parents, teachers and children aged nine years and more completed parallel forms of the EAS questionnaire. Confirmatory factor analysis was used to examine the fit between the original factors and the data. Internal consistency of each subscale, inter-rater and external validity were also examined. Children-rated EAS showed the best indices of fit between the four hypothesized factors and the data, but internal consistency was generally lower than in adult-rated questionnaires. Shyness and sociability showed significant overlap in both parent and teacher-rated EAS. The low concordance between child and adult-ratings indicates that temperament evaluation and interpretation of items may be influenced by subjective and/or developmental factors. Results are discussed in the perspective of validity versus cross-cultural comparability of temperament measurement. The theoretical four-factor structure was not completely replicable in our sample.

Child↗
PubMed2007

QSAR models for predicting the activity of non-peptide luteinizing hormone-releasing hormone (LHRH) antagonists derived from erythromycin A using quantum chemical properties.

Multiple linear regression (MLR) combined with genetic algorithm (GA) and Bayesian-regularized Genetic Neural Networks (BRGNNs) were used to model the binding affinity (pK(I)) of 38 11,12-cyclic carbamate derivatives of 6-O-methylerythromycin A for the Human Luteinizing Hormone-Releasing Hormone (LHRH) receptor using quantum chemical descriptors. A multiparametric MLR equation with good statistical quality was obtained that describes the features relevant for antagonistic activity when the substituent at the position 3 of the erythronolide core was varied. In addition, four-descriptor linear and nonlinear models were established for the whole dataset. Such models showed high statistical quality. However, the BRGNN model was better than the linear model according to the external validation process. In general, our linear and nonlinear models reveal that the binding affinity of the compounds studied for the LHRH receptor is modulated by electron-related terms.

Animals↗
PubMed2003

Lichtenstein tension-free hernioplasty: its inception, evolution, and principles.

To circumvent the degenerative nature of inguinal hernias and adverse effect of suture line tension, the Lichtenstein tension-free hernioplasty began in 1984 and evolved (between 1984 and 1988) to a procedure that is now considered the gold standard of hernia repair by the American College of Surgeons. The objective of this paper is to outline the reasons behind the minor changes made during the short, 4-year evolution of the technique, describe the key principles of the operation, and introduce a new mesh that, if elected to be used, automatically satisfies all the key principles of the procedure and guides the surgeon to perform the operation correctly. The worldwide reported result of the operation by experts and nonexperts alike is a recurrence and complication rate of less than 1%. When the key principles of the procedure, which, as reported by many authors, are easy to learn, perform, and teach, are respected, the operation results in an effectiveness (external validation) that is virtually the same as its efficacy (results of the experts), attesting to the simplicity of the procedure.

Abdomen↗
PubMed2005

Repetitive behavior profiles in Asperger syndrome and high-functioning autism.

Although repetitive behaviors are a core diagnostic domain for autism spectrum disorders, research in this area has been neglected. This study had two major aims: (1) to provide a detailed characterization of repetitive behaviors in individuals with Asperger Syndrome (AS), high-functioning autism (HFA), and typically developing controls (TD); and (2) to examine whether differences in repetitive behavior profiles could provide evidence for the external validity of AS separate from HFA. Specifically, it was hypothesized that circumscribed interests would be more prevalent and cause more impairment in the AS group than the HFA group, while the reverse would be true for other categories of repetitive behavior. The parent(s) of 61 children and adolescents (19 with AS, 21 with HFA, and 21 TD) completed two interviews focused specifically on lifetime and current repetitive behavior symptoms. No reliable differences in repetitive behavior between AS and HFA children were found. Results suggested that circumscribed interests differ in developmental course from the three other DSM-IV-TR categories of repetitive behavior. Internal consistency among the four DSM-IV-TR categories of repetitive behavior was high, alpha = .84, providing evidence for a unitary repetitive behaviors factor. The importance of expanding research in the repetitive behavior domain is highlighted as part of the necessary integration of behavioral and neurobiological approaches to understanding the etiology of autism.

Adolescent↗
PubMedDate not supplied

Genetic algorithms and self-organizing maps: a powerful combination for modeling complex QSAR and QSPR problems.

Modeling non-linear descriptor-target activity/property relationships with many dependent descriptors has been a long-standing challenge in the design of biologically active molecules. In an effort to address this problem, we couple the supervised self-organizing map with the genetic algorithm. Although self-organizing maps are non-linear and topology-preserving techniques that hold great potential for modeling and decoding relationships, the large number of descriptors in typical quantitative structure-activity relationship or quantitative structure-property relationship analysis may lead to spurious correlation(s) and/or difficulty in the interpretation of resulting models. To reduce the number of descriptors to a manageable size, we chose the genetic algorithm for descriptor selection because of its flexibility and efficiency in solving complex problems. Feasibility studies were conducted using six different datasets, of moderate-to-large size and moderate-to-great diversity; each with a different biological endpoint. Since favorable training set statistics do not necessarily indicate a highly predictive model, the quality of all models was confirmed by withholding a portion of each dataset for external validation. We also address the variability introduced onto modeling through dataset partitioning and through the stochastic nature of the combined genetic algorithm supervised self-organizing map method using the z-score and other tests. Experiments show that the combined method provides comparable accuracy to the supervised self-organizing map alone, but using significantly fewer descriptors in the models generated. We observed consistently better results than partial least squares models. We conclude that the combination of genetic algorithms with the supervised self-organizing map shows great potential as a quantitative structure-activity/property relationship modeling tool.

Algorithms↗
PubMed2004

Population pharmacokinetic modeling of subcutaneously administered etanercept in patients with psoriasis.

The objective of this paper is to present a population PK model which adequately describes the time-concentration profiles of different doses of ctanercept (Enbrel) administered subcutaneously to subjects with moderate-to-severe psoriasis and to simulate the time courses of concentrations following 50 mg once weekly (QW) dosing. Pharmacokinetic (PK) data from three clinical studies with doses 25 mg QW 25 mg twice weekly (BIW) and 50 mg BIW, were used. A one-compartment model with gender, weight and time covariates on the apparent clearance and weight covariate on the apparent volume of distribution was developed. The population mean of the apparent steady state clearance in males was 0.129 l/h. compared to 0.148 l/h in females. The clearance varied with time being lower in the first 2 weeks of the therapy, increasing sharply during weeks 3-4. and converging gradually after that to its steady state level. The population mean of the apparent volume of distribution also varied with time and was 16.11 during week 1, 20.01 during weeks 2-4 and 22.51 after week 4. The population PK model adequately described the observed concentration-time profiles in subjects with psoriasis. Despite a somewhat different covariate set, the parameter estimates of the population PK model for etanercept are very similar between the psoriasis and rheumatoid arthritis populations. The population PK model was used to simulate the pharmacokinetic profiles after a novel 50 mg QW dosing regimen. The simulations show good agreement with the observed data from 84 subjects participating in a fourth study (50 mg QW dose) used as an external validation set. The simulations of the 50 mg QW and the 25 mg BIW dosing regimens show that there is a significant overlap between the profiles yielding similar steady state exposures with both dosing regimens. The latter is an indication that the respective efficacy and safety profiles after those two dosing regimens are likely to be similar.

Computer Simulation↗
PubMed2006

A novel RBF neural network training methodology to predict toxicity to Vibrio fischeri.

This work introduces a neural network methodology for developing QSTR predictors of toxicity to Vibrio fischeri. The method adopts the Radial Basis Function (RBF) architecture and the fuzzy means training strategy, which is fast and repetitive, in contrast to most traditional training techniques. The data set that was utilized consisted of 39 organic compounds and their corresponding toxicity values to Vibrio fischeri, while lipophilicity, equalized electronegativity and one topological index were used to provide input information to the models. The performance and predictive ability of the RBF model were illustrated through external validation and various statistical tests. The proposed methodology can be used to successfully model toxicity to Vibrio fischeri for a heterogeneous set of compounds.

Aliivibrio fischeri↗
PubMed1993

Canadian Amiodarone Myocardial Infarction Arrhythmia Trial (CAMIAT): rationale and protocol. CAMIAT Investigators.

The Canadian Amiodarone Myocardial Infarction Trial (CAMIAT) is a multicenter, triple-blind, randomized, placebo-controlled trial. Eligible patients are those found on 24-hour ambulatory electrocardiographic monitoring within 6-45 days of acute myocardial infarction to have ventricular premature depolarizations (VPDs) that are frequent (> or = 10/hr) or repetitive (> or = 1 three-beat run of ventricular tachycardia). Consenting patients are randomized to amiodarone or placebo with an oral loading dose of 10 mg/kg/day for 2 weeks; maintenance dose is 300-400 mg/day for 3.5 months, 200-300 mg/day for 4 months, and 200 mg/day for 5 or 7 days/week for 16 months. Patients are followed by alternate telephone and clinical visit at 2-month intervals for 24 months. The principal outcome is a composite of presumed arrhythmic death or resuscitated ventricular fibrillation. Outcomes are determined by an external validation committee. The anticipated rate of arrhythmic death is 7.5% over 2 years; the sample size is 1,200 patients. CAMIAT began in June 1990 and is anticipated to conclude enrollment by June 1994 and follow-up by June 1995. Recruitment rate is about 92% of projected.

Amiodarone↗
PubMed1993

Applying quantitative methods to the prediction of full functional recovery in adult rehabilitation patients.

The purpose of this project was to construct a pilot prognostic index for use in research and clinical practice that would predict functional recovery in adult rehabilitation patients at discharge using clinical characteristics at admission to rehabilitation (independent performance of seven activities of daily living and three basic mobility tasks). We constructed the index from retrospectively collected data on 1,020 adult rehabilitation patients who underwent rehabilitation between 1980 and 1986. Adjusting for patient characteristics, the odds of recovering independent function doubled for each ten-point increase in the 100-point functional status score measured at admission to rehabilitation (odds ratio = 2.1, 95% confidence interval [CI] = 1.9 to 2.4). The odds increased by a factor of 1.9 (95% CI = 1.1 to 3.2) in patients with an impairment considered more functionally reversible and by a factor of 2.1 (95% CI = 1.3 to 3.4) in patients transferred from an acute hospital. The odds of functional recovery decreased in those over 79 years of age, in those who were unemployed before hospitalization, and as the number of comorbid conditions increased. Our findings demonstrate the feasibility of developing quantitative estimates of functional prognosis. Prior to use, the index should be externally validated in different rehabilitation facilities.

Activities of Daily Living↗
PubMed1990

Stress and blood glucose in type II diabetes mellitus.

Six adults with non-insulin dependent diabetes mellitus participated in a laboratory procedure to determine the effects of an acute stressor, mental arithmetic, on blood glucose, cardiovascular, and subjective indices of stress. They then completed 12 days home monitoring of stressful events, subjective stress, and blood glucose. Diet and activity were controlled to evaluate the direct effects of stress on blood glucose in the natural environment. Laboratory results showed significant increases in blood glucose, cardiovascular (HR and SBP), and subjective stress ratings during the mental arithmetic task when compared to a resting condition. Home monitoring data were consistent with the laboratory findings; blood glucose range tended to be greater on high vs low stress days, especially when the difference between high and low stress was greatest. These findings suggest that the laboratory stress induction procedure was externally valid and that in the natural environment, stress has a hyperglycemic effect on blood glucose.

Arousal↗
PubMed1995

Self selection and sample selection in a treatment study of social phobia.

The external validity or generalizability of a treatment outcome study may be influenced by the choices patients make (self-selection) and by study requirements intended to increase internal validity or protect subject welfare (e.g. sample selection). Although these effects are well-known, they have rarely been studied, and little is known about the impact they may have on generalizability of findings. In this study, subjects accepting random assignment to a larger study examining pharmacologic and cognitive-behavioral treatments for social phobia were compared with subjects refusing random assignment (i.e. self-selected) and excluded subjects (i.e. "sample-selected"). "Acceptors" differed from "refusers" on some measures suggesting that they have a lower annual income and may have fewer social supports. Therefore, they may have fewer available resources and might be more willing to accept help wherever it is offered. Despite these differences, acceptors differed from refusers on just one pretreatment measure of clinical functioning. Excluded subjects did not differ from refusers or acceptors on demographic or pretreatment clinical measures. Refusers and excluded subjects were treated with the same cognitive-behavioral treatment used in the comparative outcome study, and their posttreatment data were compared with the subgroup of acceptors who were randomly assigned to that treatment. Again, there were few significant differences. These results suggest that while self-selection and sample selection may have influenced some characteristics of the sample in this comparative outcome study, the three groups of subjects were clinically similar and responded similarly to cognitive-behavioral treatment of social phobia.

Adult↗
PubMed1982

Period effects, generation effects and age effects in peptic ulcer mortality.

The interpretation of secular trends in terms of period, age and cohorts is illustrated by data on peptic ulcer mortality for England and Wales from 1900 to 1977. Approaches to the external validation of the inferences made from such analyses are also illustrated. These data conform with predictions from a cohort analysis of some 20 years ago that peptic ulcer mortality and morbidity would decline.

Age Factors↗
PubMed1985

Memory for verbal and nonverbal stimuli in learning disability subgroups: analysis by selective reminding.

Memory for verbal and nonverbal stimuli was evaluated using selective reminding procedures in normal achieving children and four groups of disabled learners: (1) reading-spelling disabled (R-S); (2) reading-spelling-arithmetic disabled (R-S-A); (3) spelling-arithmetic disabled (S-A); and (4) arithmetic disabled (A). Each child received two analogous free-list memory tasks, one for verbal material (animal names) and the other for nonverbal material (random dot patterns). These tasks were administered using selective reminding procedures that permit separation of storage and retrieval aspects of memory by reminding children only of those words not recalled on previous trials. Results revealed that relative to controls, the A and S-A children had significantly lower storage and retrieval scores on the nonverbal task, but did not differ on the verbal task; the R-S children differed only on retrieval scores from the verbal task; and the R-S-A children on retrieval scores on the verbal task and storage and retrieval scores on the nonverbal task. Thus, results indicate that the memory performance of disabled learners varies according to (1) the type of learning problem (arithmetic vs reading), (2) the nature of the stimuli (verbal vs nonverbal), and (3) the aspect of memory being assessed (storage vs retrieval). This study provides external validation for the classification of disabled learners according to patterns of academic achievement, demonstrating a useful procedure for dealing with the intrasubject variability characteristic of disabled learners.

Achievement↗