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Results for “External validity”

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At least 1,495 records · Page 83Linked to original sources
PubMed2000

Can warfarin randomized trials be reproduced in 'real life'? Adherence to warfarin guidelines for intensity of anticoagulation in a university-based warfarin clinic.

BACKGROUND: Subjects in clinical trials may benefit from the increased attention and specific focus of the trial, thereby limiting the external validity of clinical trial results to clinical practice. Our study evaluated adherence to guidelines for intensity of anticoagulation in a large, university-based warfarin clinic to assess the generalizability of randomized clinical trials of warfarin efficacy to clinical practice. METHODS: We reviewed anticoagulation clinic records of 480 patients observed for up to 2 years to determine the amount of time anticoagulation was within the recommended therapeutic range. RESULTS: The most common indication for warfarin use was atrial arrhythmia (51.5%). Overall, anticoagulation was within the intended international normalized ratio (INR) target range on 57.8% of treatment days. Nontherapeutic treatment days were due more commonly to subtherapeutic INR values (27.6+/-25.7%) than supratherapeutic INR values (14.9+/-17.0%). This pattern was seen across all warfarin indications. CONCLUSION: These data are comparable to those reported from large randomized trials and thus support the generalizability of clinical trials of long-term warfarin anticoagulation to clinical practice.

Adolescent↗
PubMed2000

Culture, ritual, and errors of repudiation: some implications for the assessment of alternative medical traditions.

In this article, sources of error that are likely involved when alternative medical traditions are assessed from the standpoint of orthodox biomedicine are discussed. These sources include (1) biomedicine's implicit reductive materialism (manifested in its negative orientation toward placebo effects), (2) a related bias against ritual, and (3) cultural barriers to the construction of externally valid protocols. To overcome these biases, investigators must attend to ritualistic elements in alternative treatments and should recruit patients from appropriate cultural groups. Collaborative research may be the key. Benefits of collaborative research include (1) increased mutual respect and integration between culturally distinct groups and practices, (2) increased understanding and use of sophisticated techniques of empirical analysis among practitioners from the alternative traditions, (3) increased appropriation of the therapeutic benefits of ritual, and (4) enhanced overall benefit for patients of all cultural backgrounds.

Complementary Therapies↗
PubMed2000

[Clinical trials in bronchial asthma].

Most of the clinical trials with new drugs on the treatment of asthma are carried out in well selected patients who are not representative of a very clinically heterogeneous disease, with periodic controls differing from those normally undertake in the general practice and specialist consultations. The clinical trials are usually performed over very short periods of time while the normal pharmacologic treatment of asthma requires prolonged treatment. The external validity of these studies is unknown but it is probably not comparable to internal validity. To improve the quality of the clinical trials on asthma, studies should be carried out on patients representing the global population in conditions which are closer to those of the real world and during prolonged periods of time.

Asthma↗
PubMed2000

Identification and characterization of sera from HIV-infected individuals with broad cross-neutralizing activity against group M (env clade A-H) and group O primary HIV-1 isolates.

A previous study on cross-clade neutralization activity, identified three key isolates, MNlab (envB/gagB; X4 coreceptor), VI525 (envG/gagH, envA/gagA; R5X4) and CA9 (Group O; R5), that allowed discrimination of sera, likely or unlikely to neutralize primary HIV-1 isolates belonging to Group M (env clades A-H) and Group O. The prognostic ability of these three isolates was verified by means of an external validation on a different and larger set of sera. A total of 79 different sera (66 HIV-1, 10 HIV-2, 1 HIV-1+2 and 2 SIV(cpz)) were examined first for their capacity to neutralize the three key isolates, next sera were challenged against 12 other primary HIV-1 isolates of Group M (env A-H) and 2 isolates of Group O. Sera that neutralized all three isolates with an ID(50) titer of > or =1/40, also neutralized the 14 other primary isolates belonging to different genetic groups and clades. Sera that did not neutralize all three isolates did not exert broad cross-neutralizing activity. The neutralizing activity was antibody-mediated because it was absorbed and eluted from a Prot-G column. Competition-neutralization experiments using recombinant gp120 (HIV-1 MNlab) reduced the neutralizing capacity, suggesting that the neutralizing antibodies were directed against the Env protein. Remarkably, the broad cross-neutralization activity was found primarily in African female patients. In conclusion, this study confirms that three isolates are sufficient to allow identification of broad cross-neutralizing sera.

AIDS Serodiagnosis↗
PubMed2000

Age and gender differences in oppositional behavior and conduct problems: a cross-sectional household study of middle childhood and adolescence.

Behavior problems among youths cannot be understood without explaining their age and gender differences, but age and gender differences cannot be explained until they have been accurately described. In a household survey of 1,285 youths aged 9 to 17 years, there were no gender differences in oppositional behavior, but aggression, property offenses, and status offenses were more common among boys. Levels of oppositional behavior were greater at younger ages, aggression peaked near the middle of this age range, and property and status offenses were more prevalent at older ages. These findings are generally consistent with developmental models of conduct problems but are inconsistent with a recent model of gender differences and raise questions about the external validity of current taxonomies.

Adolescent↗
PubMed2000

Assessment of patient sociodemographic variables in clinical trials--can patient characteristics make a difference?

INTRODUCTION: The recruitment of patients into clinical trials is often thought to be a selective process whereby non-biological variables such as education, occupation, family/social support, and socioeconomic status are often found to be predictive of patient volunteers. This paper considers whether the susceptibility of trials to recruit non-representative patient populations may impair the extrapolation of results to diverse sociodemographic patient groups and/or hinder operational trial efficiency. METHOD: A review of the Embase and Medline databases was conducted using Subject Headings (clinical trial or randomised-controlled trial) combined with Keywords (sociodemographic, education, occupation or socioeconomic). References presenting patient sociodemographic characteristics in relation to trial recruitment or impact on measured trial data points were reviewed. RESULTS: Both quantitative and qualitative reports suggest clinical trials are prone to recruit biased sociodemographic cohorts. This review suggests three trial cohort analyses that may enhance the interpretation of trial results and provide insight into the operational efficiency of clinical trials. Assessments include: (1) comparing recruited trial cohort with source population; (2) assessing trial data points across sociodemographic groupings irrespective of treatment; (3) assessment of patient dropouts based on sociodemographic characteristics. CONCLUSION: In view of the known sociodemographic disparities found in trial recruitment, a methodology is suggested which may provide valuable information regarding the external validity of trial results and/or assessing operational trial efficiency. The challenge to those undertaking clinical trials should be to firstly determine whether recruitment biases may exist, and secondly whether trial integrity may be compromised by the presence of such biases.

Clinical Trials as Topic↗
PubMed2000

A systematic review of comparisons of effect sizes derived from randomised and non-randomised studies.

BACKGROUND: There is controversy about the value of evidence about the effectiveness of healthcare interventions from non-randomised study designs. Advocates for quasi-experimental and observational (QEO) studies argue that evidence from randomised controlled trials (RCTs) is often difficult or impossible to obtain, or is inadequate to answer the question of interest. Advocates for RCTs point out that QEO studies are more susceptible to bias and refer to published comparisons that suggest QEO estimates tend to find a greater benefit than RCT estimates. However, comparisons from the literature are often cited selectively, may be unsystematic and may have failed to distinguish between different explanations for any discrepancies observed. OBJECTIVES: The aim was to investigate the association between methodological quality and the magnitude of estimates of effectiveness by comparing systematically estimates of effectiveness derived from RCTs and QEO studies. Quantifying any such association should help healthcare decision-makers to judge the strength of evidence from non-randomised studies. Two strategies were used to minimise the influence of differences in external validity between RCTs and QEO studies: a comparison of the RCT and QEO study estimates of effectiveness of any intervention, where both estimates were reported in a single paper a comparison of the RCT and QEO study estimates of effectiveness for specified interventions, where the estimates were reported in different papers. The authors also sought to identify study designs that have been proposed to address one or more of the problems often found with conventional RCTs. METHODS DATA SOURCES: Relevant literature was identified from: The Cochrane Library, MEDLINE, EMBASE, DARE, and the Science Citation Index. References of relevant papers already identified experts. Electronic searches were very difficult to design and yielded few papers for the first strategy and when identifying study designs. CHOICE OF INTERVENTIONS TO REVIEW FOR STRATEGIES 1 AND 2: For strategy 1, any intervention was eligible. For strategy 2, interventions for which the population, intervention and outcome investigated were anticipated to be homogeneous across studies were selected for review: Mammographic screening (MSBC) of women to reduce mortality from breast cancer. Folic acid supplementation (FAS) to prevent neural tube defects in women trying to conceive. DATA EXTRACTION AND QUALITY ASSESSMENT: Data were extracted by the first author and checked by the second author. Disagreements were negotiated with reference to the paper concerned. For strategy 1, study quality was scored using a checklist to assess whether the RCT and QEO study estimates were derived from the same populations, whether the assessment of outcomes was 'blinded', and the extent to which the QEO study estimate took account of possible confounding. For strategy 2, a more detailed instrument was used to assess study quality on four dimensions: the quality of reporting, the generalisability of the results, and the extent to which estimates of effectiveness may have been subject to bias or confounding. All quality assessments were carried out by three people. DATA SYNTHESIS AND ANALYSIS: For strategy 1, pairs of comparisons between RCT and QEO study estimates were classified as high or low quality. Seven indices of the size of discrepancies between estimates of effect size and outcome frequency were calculated, where possible, for each comparison. Distributions of the size and direction of discrepancies were compared for high- and low-quality comparisons. FOR STRATEGY 2, THREE ANALYSES WERE CARRIED OUT: Attributes of the instrument were described by k statistics, percentage agreement, and Cronbach's a values. Regression analyses were used to investigate -variations in study quality. (ABSTRACT TRUNCATED)

Breast Neoplasms↗
PubMed2001

[Why researchers excluded women from their trial populations].

Women are still, but to a lesser extent than twenty years ago, excluded as subjects of medical research on diseases that are prevalent among both men and women. To discover the basis on which women were excluded, the research ethics committee requested a written explanation. In all, 26 such project applications were identified during 1997-1999 (2% of the total number of applications during the period). Most researchers had more than one reason for exclusion. Qualitative analysis revealed that these explanations could be grouped into three categories, depending on whether women were excluded for scientific, historical or economic reasons. The scientific reasons correspond mainly to a lack of pertinent knowledge of the physiology and metabolism of women of childbearing age. Consequently, results lacked external validity. Perhaps the lack of knowledge of women's physiology and metabolism could be explained by a lack of female experimental animals in pre-clinical studies. One notes however a general concern not to harm women of childbearing age. The historical reasons underlie the tendency to repeat studies on former study populations that happened to be composed of men. Finally, tight research budgets restricted the participation of women but not of men. The Swedish Medical Research Council issued a policy document in 1998 to the effect that research ethics committees could require additional information concerning choice of study population. This study demonstrates an avoidable occurrence of gender bias in medical research.

Clinical Trials as Topic↗
PubMed2001

The statistical comparison of clinical trials.

Being able to compare clinical trials using statistically proven analyses is essential, but certain protocols must be followed if such a comparison is to be made. The difficulty of making meaningful statistical comparisons is illustrated in 5 clinical trials comparing atypical antipsychotics. Certain judgments can be made on the basis of internal and external validity, for example, but there are many other areas--effect size, for example--in which it is impossible to make any statistical comparisons across these trials because they were not conducted in a uniform fashion. In the final analysis, it is doubtful that the differences between atypical antipsychotics covered in these trials are greater than those due to chance.

Antipsychotic Agents↗
PubMed1998

Groin hernia surgery: a systematic review.

BACKGROUND: An extensive volume of clinical research has been undertaken on the use of surgery for groin hernias. For many years there has been a large number of different methods of repairing hernias and, with the introduction of laparoscopic surgery, this has increased further. It is uncertain which method is the best in terms of safety and effectiveness. OBJECTIVES: This review was undertaken to compare the outcomes following different surgical procedures to treat groin hernias in adults. It sought answers to six questions: 1)Which method of surgery (including open procedures and laparoscopic surgery) is the safest and most effective for inguinal hernia repair? 2) Is local anaesthesia a safe and effective alternative to general anaesthesia? 3) Is there a difference in outcome between specialist and non-specialist surgeons? 4) Is day-case as safe and effective as inpatient surgery? 5) Is synchronous bilateral hernia repair as safe and effective as delayed repair? 6) Which method of surgery is the safest and most effective for femoral hernia repair? METHODS: The primary measure of effectiveness used was the proportion of hernia repairs in which there was a recurrence. Secondary outcome measures included complications, post-operative pain, wound infection, time to return to normal activities and/or return to work. A systematic search of the literature (up to February 1996) was undertaken using a variety of approaches. the methodological quality of all prospective comparative studies (45 randomised trials and 26 non-randomised trials/prospective cohort studies) was assessed using a standard checklist. RESULTS: Some of the variation in findings from different studies is likely to be due to methodological differences rather than differences in the effectiveness of the surgical procedures. The main methodological shortcomings of the studies that have been performed are: lack of agreed method for assessing severity of hernias; failure to take confounding into account in non-randomised studies; variation in length of follow-up; poor external validity; lack of objective measures of outcome; and inadequate statistical power. These problems severely limit the conclusions that can be drawn from the literature.

Adult↗
PubMed2001

From paper-based to electronic guidelines: application to French guidelines.

In order to develop an internet-based decision support system, making available for French general practitioners several prevention guidelines is was necessary to implement paper based guideline. We propose a framework allowing to transform paper based practice guideline into their electronic form. Three different problems were identified: computability (e.g. determinism of the eCPG), logic (e.g. ambiguities when combining Booleans operators) and external validity (i.e. stability of decision for variations around thresholds and proportion of subjects classified in the various terminal nodes). The last problem concerned documentation of evidence: the level of evidence was associated only with the terminal decision node and not with the pathway through the decision tree. We concluded that computerisation of guidelines is not possible without expertise or authors advice. To improve computability it is necessary to provide authors with a framework that checks ambiguities, and logical errors.

Algorithms↗
PubMedDate not supplied

Quantifying tobacco related health care expenditures in the Republic of the Marshall Islands: a case study in determining health costs in a developing US associated island nation.

OBJECTIVES: This case study examines the advantages, disadvantages, and utility of three research methods to measure the medical costs of tobacco use in the Republic of the Marshall Islands (RMI). METHODS: The authors used the morbidity-based models, models based on the difference in utilization of medical facilities between smokers and non-smokers, and models of inter-country comparisons. FINDINGS: In the RMI, morbidity models would have a propensity to grossly under-estimate the medical costs of tobacco use. Models that measure the difference in medical service utilization between smokers and non-smokers can be confounded by cultural factors and by the level of health care that is provided. The RMI population structure affected the sampling methods. The external validity of the survey instrument may be increased through measuring more parameters with greater precision. Inter-country comparisons may be used to approximate and set upper and lower limits of costs for past medical costs, and may be the only method to determine future health care costs from tobacco use. CONCLUSIONS: Determining medical costs of tobacco use in an US Associated island nation with an under-developed health care infrastructure has not been previously attempted. There were significant methodological challenges that were encountered. Health, economic, cultural, and research environments in the RMI are unique and require innovative methods to determine medical costs associated with tobacco use. Direct application of the methodologies utilized in the United States to determine medical costs of tobacco use may grossly under-estimate the medical cost of tobacco use in the RMI. The research challenges can be addressed.

Developing Countries↗
PubMed2001

Structure-specificity relationships for haloalkane dehalogenases.

A structural analysis of the substrate specificity of hydrolytic dehalogenases originating from three different bacterial isolates has been performed using the multiple computer-automated structure evaluation methodology. This methodology identifies structural fragments in substrate molecules that either activate or deactivate biological processes. The analysis presented in this contribution is based on newly measured dehalogenation data combined with data from the literature (91 substrates). The enzymes under study represent different specificity classes of haloalkane dehalogenases (haloalkane dehalogenase from Xanthobacter autotrophicus GJ10, Rhodococcus erythropolis Y2, and Sphingomonas paucimobilis UT26). Three sets of structural rules have been identified to explain their substrate specificity and to predict activity for untested substrates. Predictions of activity and inactivity based on the structural rules from this analysis were provided for those compounds that were not yet tested experimentally. Predictions were also made for the compounds with available experimental data not used for the model construction (i.e., the external validation set). Correct predictions were obtained for 28 of 30 compounds in the validation set. Incorrect predictions were noted for two substrates outside the chemical domain of the set of compounds for which the structural rules were generated. A mechanistic interpretation of the structural rules generated provided a fundamental understanding of the structure-specificity relationships for the family of haloalkane dehalogenases.

Biodegradation, Environmental↗
PubMed2001

A multidimensional meta-analysis of treatments for depression, panic, and generalized anxiety disorder: an empirical examination of the status of empirically supported therapies.

The authors report a meta-analysis of high-quality studies published from 1990-1998 on the efficacy of manualized psychotherapies for depression, panic disorder, and generalized anxiety disorder (GAD) that bear on the clinical utility and external validity of empirically supported therapies. The results suggest that a substantial proportion of patients with panic improve and remain improved; that treatments for depression and GAD produce impressive short-term effects: that most patients in treatment for depression and GAD do not improve and remain improved at clinically meaningful follow-up intervals: and that screening procedures used in many studies raise questions about generalizability, particularly in light of a systematic relation across studies between exclusion rates and outcome. The data suggest the importance of reporting, in both clinical trials and meta-analyses, a range of outcome indices that provide a more comprehensive, multidimensional portrait of treatment effects and their generalizability. These include exclusion rates, percent improved, percent recovered, percent who remained improved or recovered at follow-up, percent seeking additional treatment at follow-up, and data on both completer and intent-to-treat samples.

Anxiety Disorders↗
PubMed2001

[An observational study requires careful consideration by the reader].

The observational study has its merits when randomized controlled studies are impossible to perform. This review discusses its merits and weaknesses for a reader of such studies. The reader has to consider the internal and external validity of the study and its role in the establishment of causal relationships and estimations of risks. The reader is recommended to primarily evaluate the quality of study design, confounding and measurement bias, rather than to try to understand if an advanced statistical analysis is correct. The possibilities of misleading results are discussed.

Bias↗
PubMed2002

Issues in pooling administrative data for economic evaluation.

Managed care, in particular the health maintenance organization (HMO), now dominates US healthcare delivery, and economic evaluation is receiving increasing attention as a management tool that can be tailored to its perceived business needs. This encourages use of HMO administrative data as an efficient source of resource utilization and cost measures. Use of administrative data coincides with growing research interest in multisite analyses that increase external validity. The best alternative to a nationally representative data set is to pool administrative data from multiple sites within one database. However, pooling administrative data is problematic because HMO data sources reflect differences in systems of care, costing, and coding. This paper describes issues inherent in the pooling of HMO administrative cost data for use in multisite economic evaluations. We describe the attributes of administrative data that are relevant to costing and discuss their implications for multisite economic evaluations. We then briefly describe our experience with pooling multisite cost data, discuss lessons learned, and offer suggestions for researchers working with such data, followed by concluding comments. Multisite administrative data provide unique opportunities to conduct population-based clinical and economic research.

Community Health Planning↗
PubMed2002

The unexpected influence of physician attributes on clinical decisions: results of an experiment.

UNLABELLED: This experiment was designed to determine: (1) whether patient attributes (specifically a patient's age, gender, race, and socioeconomic status) independently influence clinical decision-making; and (2) whether physician characteristics alone (such as their gender, age, race, and medical specialty), or in combination with patient attributes, influence medical decision-making. METHODS: An experiment was conducted in which 16 (= 2(4)) videotapes portraying patient-physician encounters for two medical conditions (polymyalgia rheumatica (PMR) and depression) were randomly assigned to physicians for viewing. Each video presented a combination of four patient attributes (65 years or 80 years of age; male or female; black or white; blue or white collar occupation). Steps were taken to enhance external validity. One hundred twenty-eight eligible physicians were sampled from the northeastern United States, with numbers balanced across 16 (= 2(4)) strata generated from the following characteristics (male or female; < 15 or > or = 15 years since graduation; black or white; internists or family practitioners). The outcomes studied were: 1) the most likely diagnosis; 2) level of certainty adhering to that diagnosis; and 3) the number of tests that would be ordered. RESULTS: Patient attributes (namely age, race, gender, and socioeconomic status) had no influence on the three outcomes studied (the most likely diagnosis, the level of certainty, and test ordering behavior). This was consistent across the two medical conditions portrayed (PMR and depression). In contrast, characteristics of physicians (namely their medical specialty, race, and age) interactively influenced medical decision-making. CONCLUSION: Epidemiologically important patient attributes (which Bayesian decision theorists hold should be influential) had no effect on medical decision-making for the two conditions, while clinically extraneous physician characteristics (which should not be influential) had a statistically significant effect. The validity of idealized theoretical approaches to medical decision making and the usefulness of further observational approaches are discussed.

Age Factors↗
PubMed1993

Methodology of the National Survey of Sexual Attitudes and Lifestyles.

"The preparation and fieldwork for the National Survey of Sexual Attitudes and Lifestyles was carried out between 1987-1991. The survey was a combination of a face-to-face interview and self-completion questionnaire and comprised 18,876 individuals aged 16-59 years in Great Britain. The response rate was similar to other sample surveys on less sensitive topics. Women were overrepresented but the distributions of other demographic characteristics were similar to other data sets. The external validity and internal consistency of the data were found to be adequate. The likely sources and effects of bias are discussed."

Attitude↗