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Results for “External validity”

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At least 1,063 records · Page 59Linked to original sources
PubMed1998

The semi-structured affective temperament interview (TEMPS-I). Reliability and psychometric properties in 1010 14-26-year old students.

BACKGROUND: The purpose of this study was to evaluate the reliability and psychometric properties of the Semistructured Affective Temperament Interview, and determine cut-offs for each temperament. METHOD: 1010 Italian students aged between 14 and 26 were evaluated by means of the Akiskal and Mallya criteria in a Semistructured Interview for depressive, cyclothymic, hyperthymic, and irritable temperaments. RESULTS: This instrument has very good reliability and internal consistency. The percentage of subjects with a z-score higher than the second positive standard deviation ( + 2 SD) on the scales of depressive and cyclothymic temperaments are 3.6% and 6.3% (reaching scores of 7/7 and 9/10), respectively. Hyperthymic traits, on the other hand, are widespread in our sample: most subjects are included within the second positive standard deviation ( + 2 SD), and 8.2% of these reach a 7/7 score; therefore, the problem of defining a cut-off for this temperament is still open. By contrast, the irritable temperament is rare, conforming to a non-gaussian distribution, with 2.2% of cases above the second positive standard deviation ( + 2 SD). LIMITATION: The data are based on subject report without collateral information and external validation. CONCLUSION: This study contributes to more accurate definition of cut-offs for individual temperament scales. The standardization of the interview thus makes it possible to compare three out of four temperamental scales, showing the dominant temperamental characteristics for each subject. Prospective studies are needed to demonstrate the stability of these traits over time.

Adolescent↗
PubMed2004

Considering the complexity of microbial community dynamics in food safety risk assessment.

The potential for competitive inhibition to limit the growth of microbial pathogens in food raises questions about the external validity of typical predictive microbiology studies and suggests the need to consider microbial community dynamics in food safety risk assessment. Ecological theory indicates, however, that community dynamics are highly complex and may be very sensitive to initial conditions and random variation. Seemingly incongruous empirical results for Escherichia coli O157:H7 in ground beef are shown to be consistent with a simple theoretical model of interspecific competition. A potential means of incorporating community-level microbial dynamics into the food safety risk assessment process is explored.

Antibiosis↗
PubMed2003

Framingham risk function overestimates risk of coronary heart disease in men and women from Germany--results from the MONICA Augsburg and the PROCAM cohorts.

BACKGROUND: The prediction of the absolute risk of coronary heart disease (CHD) is commonly based on risk prediction equations that originate from the Framingham Heart Study. However, differences in population risk levels compromise the external validity of these risk functions. SETTING AND STUDY POPULATION: Participants aged 35-64 years from the MONICA Augsburg (2861 men and 2925 women) and the PROCAM (5527 men and 3155 women) cohorts were followed-up with regard to incident non-fatal myocardial infarction (MI) and fatal coronary events. For each participant, the predicted absolute risk of fatal plus non-fatal events was derived using Framingham risk equations. Predicted and actually observed risks were compared. RESULTS: The two cohorts were similar in their baseline characteristics. Coronary risk predicted by the Framingham risk function substantially exceeded the risk actually observed in the German cohorts, irrespective of gender. The difference between predicted and observed absolute CHD risk increased with age while the ratio of predicted over observed risk remained constant at about a value of 2. Taking potentials for underascertainment in the German cohorts due to unrecognised MI and sudden deaths into account, the residual magnitude of risk overestimation by the Framingham risk function is probably at least 50%. CONCLUSIONS: Local guidelines for the management of patients with risk factors need to correct for this overestimation to avoid inadequate initiation of treatment and inflation of costs in primary prevention. Similar studies should be conducted in other populations with the aim of defining appropriate factors that calibrate absolute risk predictions to local population levels of CHD risk.

Adult↗
PubMed1997

Use of a stochastic simulation model to identify an efficient protocol for ovarian cancer screening.

The intervention protocol for an ovarian cancer screening trial should be efficient as well as effective, because it may become the standard of care if the trial demonstrates mortality reduction. To identify an efficient ovarian cancer screening protocol, the effectiveness and cost-effectiveness of selected single modality and multimodal screening strategies were estimated using a stochastic simulation model. Screening was simulated over a 30-year period in a hypothetical cohort of 1 million women aged 50 at the beginning of the period. The net present value of the cost per year of life saved was estimated for six protocols involving transvaginal sonography (TVS) and/or the tumor antigen CA 125. Internal and external validation was performed, and sensitivity analyses were conducted to assess the robustness of the ranking of the strategies. A multimodal strategy involving CA 125 with a threshold for positivity of either elevation above 35 U/ml or doubling since the previous screen, followed by TVS only if CA 125 is positive, was found to be efficient in the sense that no other strategies saved as many years of life at lower cost per year of life saved. Used annually, this strategy cost under $100,000 per year of life saved over a range of assumptions. The model's predictions are consistent with results reported in the literature regarding the performance of TVS and CA 125. The multimodal strategy used annually or every six months was efficient compared to either ultrasound or CA 125 used alone, over a range of assumptions. Simulation of screening may be useful in selecting a screening protocol to be tested in a randomized controlled trial.

Aged↗
PubMed1997

Outcomes of a placebo run-in period in a head and neck cancer chemoprevention trial.

This study describes the outcomes of an eight-week placebo run-in period in a head and neck cancer chemoprevention trial. Of 391 former cancer patients who entered the run-in over the first two years of the trial, 91% were randomized. Pill counts showed that adherence rates ranged from 0% to 120% (mean 96%, SD = 15%). The trial did not randomize subjects who were no longer interested in trial participation (n = 20), who did not return within 10 weeks of enrollment date (n = 3), or who did not achieve a drug adherence level of at least 75% (n = 9). Three subjects were not randomized for other reasons. Univariate predictors of run-in outcome (randomized or not randomized) included ethnicity, education level, cancer site, cancer stage, and Karnofsky performance score. Multivariate analyses resulted in a logistic model with Karnofsky performance and education level as significant predictors of randomization. Persons with a Karnofsky score of 100 had 2.3 higher odds of randomization (95% CI = 1.1, 4.9) than persons with compromised Karnofsky scores, and persons with more than a high school education had 2.1 higher odds of randomization (95% CI = 1.0, 4.9) than persons with less education. These results suggest that the use of a run-in period may compromise the external validity of randomized prevention trials. More research is needed to understand further the behavioral factors underlying the observed differences so that prevention researchers can develop effective interventions for facilitating trial participation, especially in under-represented, trial-eligible groups. Investigators should expand the objectives of a run-in period to (1) evaluate why eligible persons refuse trial enrollment or fail to be randomized at the end of the run-in and (2) use the run-in period for a systematic evaluation of levels and costs of intervention strategies designed to promote trial enrollment and adherence.

Anticarcinogenic Agents↗
PubMed1997

Tracking and follow-up of 16,915 adolescents: minimizing attrition bias.

This paper reports a multi-dimensional approach to minimize drop-outs from a two-year follow-up of a clinical trial designed to reduce initiation of tobacco use in 16,915 adolescent orthodontic patients. A hierarchical approach to data collection and tracking was employed. Seventy percent of participants were reached and interviewed at home by telephone. Strategies used to survey remaining participants included calling parents' work numbers and directory assistance, reviewing orthodontists' charts, sending surveys by mail, offering incentives, and using reverse telephone directories. More than 92% of the participants completed follow-up surveys. Multivariate analyses showed that baseline tobacco and alcohol use predicted loss to follow-up. Similarly, the number of procedures used to track each participant predicted presence of risk behaviors at post-test, demonstrating that an organized tracking hierarchy curtailed even greater compromises to internal and external validity. Evaluation and costs of individual strategies are discussed.

Adolescent↗
PubMed1998

Should we adjust for covariates in nonlinear regression analyses of randomized trials?

The analyses of the primary objectives of randomized clinical trials often are not adjusted for covariates, except possibly for stratification variables. For analyses with linear models, adjustment is a precision issue only. We review the literature regarding logistic and Cox (proportional hazards) regression models. For these nonlinear analyses, omitting covariates from the analysis of randomized trials leads to a loss of efficiency as well as a change in the treatment effect being estimated. We recommend that the primary analyses adjust for important prognostic covariates in order to come as close as possible to the clinically most relevant subject-specific measure of treatment effect. Additional benefits would be an increase in efficiency of tests for no treatment effect and improved external validity. The latter is particularly relevant to meta-analyses.

Bias↗
PubMed1999

Detecting selection bias in randomized clinical trials.

Lack of concealment of allocation in randomized clinical trials can invite selection bias, which is the preferential enrollment of specific patients into one treatment group over another. For example, patients more likely to respond may be enrolled only when the next treatment to be assigned is known to be the active treatment, and patients less likely to respond may be enrolled only when the next treatment to be assigned is known to be the control. Despite the fact that selection bias can compromise both the internal and external validity of trials, little methodology has been developed for its detection. An investigator may test the success of the randomization by comparing baseline characteristics across treatment groups, but such test is limited by the potential inability of the measured baseline variables to predict response. A new method for detecting selections bias, based on response data only, is developed for the case in which a small block size, and either unmasking of treatment codes or an open-label design, have compromised the concealment of allocation. This new method complements baseline comparisons, and is sensitive to detect selection bias even in situations in which baseline comparisons are not.

Computer Simulation↗
PubMedDate not supplied

[Disagreement among hospital and community studies evaluating the same research question].

The goal of this review is to delineate some of reasons that justify the lack of consistency between hospital-based and community research. The main reasons for the differences are the selection of the hospital population and information based on clinical chart (its lack of uniformity and the treatment of the not available data). The reasons for lack of consistency are divided according to the type of research question: frequency, diagnosis, etiology, prognosis and treatment-prevention. The way a hospital population is selected justifies discrepancies regarding frequency and prognosis. As regards diagnosis, differences are mainly due the prevalence of disease. In the ascertainment of causality several biases are more common in hospital-based research, such as detection bias, protopathic (both producing an away-from-null estimate), and inclusion bias (diminishing the strength of association). Examples taken from the medical literature are offered to illustrate each bias. Regarding treatment-prevention problems arise from external validity, as clinical trials are less prone to bias; this latter situation is exemplified with an assessment of vaccine efficacy in both patients and healthy population. The frequency of citation of bias was assessed by a Medline search; in hospital studies detection bias and confounding by indication were more often quoted than in non-hospital research (RR = 2.71; 95% CI; 1.69-4.37; RR = 1.76; 95% CI, 0,90-3,42, respectively). Lastly, several recommendations are given to increase the validity of hospital-based research.

Biomedical Research↗
PubMedDate not supplied

[Strategies in measuring nursing care].

When resources are limited, the balance between the supply and the demand of nursing care is becoming more and more necessary. This situation justifies the use of tools to measure work charges in nursing. This article analyses the relationship between work charges and time estimation in nursing care. From a bibliographical review on this topic it discusses possibilities and techniques of time estimation for the nursing care given to a patient, as well as the caring time he or she requires. Two different approaches and some conclusions from the analysis of both of them are showed: first; the direct method, i.e. that of measuring caring levels; and secondly, the indirect method, that is a system for classifying patients. The interest of the direct method is advocated because of its clarity, external validation possible integration in nursing care plans.

Humans↗
PubMed2001

Pre-exposure rabies vaccination: strategies and cost-minimization study.

An alternative strategy for pre-exposure rabies vaccination to the institutional recommendations of the World Health Organization and the Centers for Disease Control and Prevention is proposed based on recent long-term follow-up of post-vaccinal seroconversion rates. The alternative strategy uses the same primary series (i.e. vaccination in the deltoid area on D0, D7, and D28), but is completed by a scheduled booster vaccination at D365. The frequency of recommended subsequent booster injections depends on the serological test results obtained by a RFFIT on D379 and 3 years later. The objective of this study was to compare the efficiency of the two pre-exposure strategies. A cost-minimization analysis was carried out to compare the two rabies pre-exposure vaccination and serological test strategies based on the data from two published studies on the long-term evolution of the immunity achieved using the different recommendations. For a theoretically equivalent immunogenicity, the cost of the alternative strategy ranged from 1.7 to 5.2 times lower than that of the institutional recommendations. A sensitivity analysis confirmed the robustness of the results. The alternative strategy should be validated externally under field conditions. This approach would compare its real efficiency to the institutional recommendations.

Antibodies, Viral↗
PubMed1998

Assessment of chronic back pain patient characteristics using factor analysis of the MMPI-2: which dimensions are actually assessed?

Guided by the study of Deardorff et al. (Pain, 54 (1993) 153-158), the MMPI-2 data from 240 chronic back pain patients were factor-analyzed in an attempt to discern the most important dimensions for this patient population. Principal components analysis with an oblique rotation revealed four underlying factors: Psychological disturbances, Extraversion-introversion, Passivity, and Somatic complaints. The factor structure reported by Deardorff et al. was thus successfully replicated. The stability of the factors was also supported using random split subsamples. External measures relevant to pain were used to investigate the external validity of Somatic complaints in a subsample of patients (n=93). Relations were found to number of painful sites, Waddell signs, fear of movement (maximal isometric flexion and extension performance by dynamometry, and cardiovascular fitness (VO2-max). Substantial differences emerged across genders. The derived MMPI-2 dimensions appear to constitute important characteristics associated with chronic pain. It is concluded that MMPI-2 research into chronic pain may become more productive when the instrument and its clinical correlates are examined within a clear conceptual framework of distress and personality relevant for chronic pain and its treatment.

Adult↗
PubMedDate not supplied

The College Alcohol Problems Scale.

A short, reliable two-factor instrument measuring drinking-related negative consequences was developed from a previous measure using two samples of college students. In Study I, data on alcohol use and problems associated with alcohol use were collected on 382 introductory psychology students. The original College Alcohol Problems Scale (CAPS) was tested and found to fit the data poorly. Sequential methods were used to develop a revised instrument. Principal components analyses (PCA) on half of the sample were conducted on 20 items written to measure negative consequences related to college student drinking. Results indicated a two-factor solution measuring social and emotional problems. Confirmatory factor analyses (CFA) on the other half of the sample confirmed the two-factor structure. Further refinement of the instrument resulted in the revised CAPS (CAPS-r), an eight-item two-factor scale. In Study II, the response format was altered to coincide with the Young Adult Problem Screening Test. A total of 726 students completed the instrument as part of a university-wide random sample. CFA showed that the hypothesized model fit well across all measures of model fit and the factor structure was invariant across gender. Additional analyses revealed that the scale was internally consistent and externally valid. A short reliable and valid measure of alcohol-related problems is needed to enable low-cost data collection on college campuses across the nation, as well as to facilitate program evaluation and routine epidemiological surveillance and monitoring.

Adolescent↗
PubMedDate not supplied

Dynamic typology clustering within the stages of change for smoking cessation.

Dynamic typology clustering was employed to find homogeneous subgroups of smokers within each of three early stages of change (precontemplation, contemplation, preparation) in a representative sample of smokers. Individual change profiles were created by coding the stage of change for each subject at five consecutive assessment points over a 2-year period (baseline and 6, 12, 18, and 24 months). A total of 446 unique change profiles were found in the sample of 2,088 smokers who had complete data for all five time points. The sample was initially split into three groups determined by baseline stage of change. Within each initial stage, subgroups that shared similar patterns of change were interpreted by examining the shape and elevation of the change profiles. Four major types of profiles emerged: a stable profile, a progressing profile, a vacillating profile, and a regressing profile. External validation revealed significant differences among the dynamic typology subtypes on key transtheoretical model constructs (processes of change, decisional balance, situational temptations). These results both support and complement key construct relationships within the transtheoretical model and can provide important predictive information to direct and enhance treatment interventions for smoking cessation.

Adult↗
PubMed1999

'Research' versus 'real-world' patients: representativeness of participants in clinical trials of treatments for cocaine dependence.

Rigorous clinical trials have been criticized as having limited external validity, and specifically that subjects participating in clinical trials are not representative of individuals seen in clinical practice. To assess the representativeness of subjects participating in clinical trials, 243 research subjects participating in clinical trials of treatments for cocaine dependence were compared to a sub-sample of 213 individuals being treated for cocaine dependence in outpatient clinical settings from a large national database. The data suggest that research findings are not invariably based on less challenging patients with mild forms of substance dependence and related problems; moreover research patients may be similar to, if not more severe than, individuals with cocaine problems seen in regular clinical settings in the community.

Adult↗
PubMed1986

Subselective measurement of coronary blood flow velocity using a steerable Doppler catheter.

The accuracy of coronary arteriography to predict obstruction to coronary blood flow has recently been questioned. Assessment of coronary hemodynamic variables and vasodilator reserve may provide more reliable information regarding the significance of coronary stenosis. To provide a clinically safe and reliable method of measuring coronary blood flow velocity and coronary flow reserve, a 3F steerable Doppler catheter capable of subselective placement in the coronary circulation was developed and validated in an animal model. Coronary blood flow velocity measured with the catheter correlated with simultaneous measurements by a previously validated external cuff type Doppler probe (r = 0.97), coronary sinus flow collections (r = 0.78) and femoral artery flow collections (r = 0.96). The extravascular Doppler cuff measurements of rest flow velocity and vasodilator reserve were not significantly different with or without the catheter in the artery, indicating that the Doppler catheter caused no obstruction to blood flow. The Doppler catheter has recorded stable and reproducible signals without complications in 28 patients, including 62 separate arterial cannulations. Thus: 1) the 3F Doppler coronary catheter is nonobstructing, steerable and safe; 2) there is an excellent correlation of blood flow velocity with volume collections; and 3) the catheter provides a reliable method of determining coronary blood flow velocity and coronary vasodilator reserve.

Animals↗
PubMed1999

A comparison of the national registry of myocardial infarction 2 with the cooperative cardiovascular project.

OBJECTIVES: This study was performed to evaluate whether or not the simpler case identification and data abstraction processes used in National Registry of Myocardial Infarction two (NRMI 2) are comparable with the more rigorous processes utilized in the Cooperative Cardiovascular Project (CCP). BACKGROUND: The increased demand for quality of care and outcomes data in hospitalized patients has resulted in a proliferation of databases of varying quality. For patients admitted with myocardial infarction, there are two national databases that attempt to capture critical process and outcome data using different case identification and abstraction processes. METHODS: We compared case ascertainment and data elements collected in Medicare-eligible patients included in the industry-sponsored NRMI 2 with Medicare enrollees included in the Health Care Financing Administration-sponsored CCP who were admitted during identical enrollment periods. Internal and external validity of NRMI 2 was defined using the CCP as the "gold standard." RESULTS: Demographic and procedure use data obtained independently in each database were nearly identical. There was a tendency for NRMI 2 to identify past medical histories such as prior infarct (29% vs. 31%, p < 0.001) or heart failure (21% vs. 25%, p < 0.001) less frequently than the CCP. Hospital mortality was calculated to be higher in NRMI 2 (19.7% vs. 18.1%, p < 0.001) due mostly to the inclusion of noninsured patients 65 years and older in NRMI 2. CONCLUSIONS: We conclude that the simpler case ascertainment and data collection strategies employed by NRMI 2 result in process and outcome measures that are comparable to the more rigorous methods utilized by the CCP. Outcomes that are more difficult to measure from retrospective chart review such as stroke and recurrent myocardial infarction must be interpreted cautiously.

Aged↗
PubMed2002

Patient-centred consultations and outcomes in primary care: a review of the literature.

Although 'patient-centred' consulting skills are increasingly seen as crucial for the delivery of effective primary care, there is significant lack of clarity over the precise definition of the term, optimal methods of measurement, and the relationship between patient-centred care and patient outcomes. The present study sought to review all empirical studies to date that have investigated the relationship between measures of patient-centred consulting and outcomes in primary care, and to examine the methodological rigour of the studies. A number of observational studies were identified, all of which reported some relationships between doctor behaviour defined as 'patient-centred' and a variety of patient health outcomes. However, the pattern of associations was not clear or consistent, and some of the studies had shortcomings in terms of their internal and external validity. Although the current evidence base may be suggestive of a relationship between patient-centred consulting behaviour and patient outcomes, the case has not been made definitively.

Humans↗