SEARCH · PubMed Health

Results for “Internal validation”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 937 records · Page 52Linked to original sources

PubMed2004

Telepsychiatry treatment outcome research methodology: efficacy versus effectiveness.

The use of videoconferencing technology to provide mental health services (telepsychiatry) offers hope for addressing longstanding problems regarding work force shortages and access to care, especially in remote or rural areas. However, data on treatment outcomes (i.e., based on randomized clinical trials) from telepsychiatry applications are virtually nonexistent, representing an important gap in the literature. An important methodological decision point in developing treatment outcome research is whether to take an efficacy or effectiveness approach. Efficacy approaches offer enhanced internal validity; however, they may have limited generalizability to real-world settings. Effectiveness approaches offer enhanced external validity. But, they are typically less controlled than efficacy studies, thereby limiting the assumptions that can be made about causality. The current state of telepsychiatry research necessitates efficacy studies, the outcomes from which can be used to inform future effectiveness studies.

Health Services Research↗

PubMed1991

The abbreviated mental test: its use and validity.

The validity of the Abbreviated Mental Test was demonstrated by comparison with final clinical diagnoses in a consecutive sample of 168 patients admitted with acute illness to a department of health care of the elderly. Fifty-eight (34%) had abnormal cognition. The best cut-off point was 8, with less than 8 suggesting abnormal cognitive function. A short version (the AMT7) of the AMT was developed. Its validity, internal consistency and coverage of domains was equivalent to the AMT but it had a slightly higher sensitivity (with acceptable specificity) than the original. This new short version may improve performance of junior doctors in clinical practice who appear to have difficulty remembering all 10 items of the AMT.

Aged↗

PubMed1989

Iron deficiency and educational achievement in Thailand.

This double-blind clinical trial was conducted in Thailand to assess the impact of iron treatment on the IQ and educational attainment of 1358 9-11-y-old children. The children were classified into one of three groups: iron replete, iron depleted, and iron-deficient anemic. The Raven Progressive Matrices was used to measure IQ. A Thai language and a math test were administered to assess school attainment. A 50-mg/d tablet of ferrous sulphate was given for 2 wk and a 100 mg/d tablet, for 14 wk. An anthelminthic drug was given on the day of the blood test before treatment and 3 mo after the intervention started. There is evidence of a positive association between iron status and IQ and a language school achievement test but there is no support for the internal validity of the hypothesis that this association is causal.

Anthelmintics↗

PubMed1992

Mortality of severely obese subjects.

All large prospective studies (n greater than 20,000) and several smaller studies have found that severe obesity [body mass index (BMI) greater than or equal to 35 kg/m2] is associated with approximately a twofold increase in total mortality and in a severalfold increase in mortality due to diabetes, cerebro-, and cardiovascular disease, and certain forms of cancer. Studies that have not been able to confirm this have been small and/or short term, have failed to control for smoking or early mortality, have controlled for intermediate risk factors in an inappropriate way, or have a reduced internal validity due to misclassification biases. As compared with BMI, abdominal obesity is a stronger predictor of mortality in most studies available. The incidence of sudden death unexplained by autopsy may be up to 40 times higher in severely obese subjects as compared with the general population. A small weight increase since the age of 18 is associated with a decreased risk whereas weight increases greater than 10 kg are associated with an increased mortality. The total mortality ratio for severe obesity decreases from 55 y of age and is not detectable above 80 y of age. Studies lacking adequate control groups indicate that a sustained weight loss may induce a reduced mortality but results from controlled intervention studies are so far not available.

Cohort Studies↗

PubMed2005

Reporting participation in epidemiologic studies: a survey of practice.

Self-selection bias may threaten the internal validity of epidemiologic studies. Studies with a low level of participation are particularly vulnerable to this bias, and commentators note apparent declines in participation in recent years. The authors therefore conducted a retrospective review to survey the practice of reporting participation in epidemiologic studies, to assess changes in participation over time, and to evaluate the impact of increased biologic specimen collection on participation. The authors abstracted selected study characteristics from 355 peer-reviewed, original, analytic-epidemiology research articles published from January 1 to April 30, 2003, in 10 high-impact general epidemiology, public health, and medical journals. At least some information regarding participation was provided in 59% of cross-sectional studies, 44% of case-control studies, and 32% of cohort studies. Participation appears to have declined during 1970-2003 for all study designs. Participation declined most steeply for controls in population-based, case-control studies (-1.86% per year, 95% confidence interval: -3.03, -0.69), with steeper declines after 1990. Proportionately more studies collected biologic specimens over time, particularly for cohort and case-control study designs (p(trend) = 0.06 and 0.03, respectively), yet participation was reported separately for the biologic specimen study component in only 27% of studies. The authors conclude that epidemiologists need to address declining participation and to report participation consistently, including for biologic specimen collection.

Bibliometrics↗

PubMed2002

A proposal for evaluation of exposure data.

There is a growing need for transparency concerning ways in which existing exposure data are weighted for their relative value and quality. Currently, this evaluation is largely subjective and is dependent on the quality of the judgement of the individual assessor or expert group. In this paper some general guidelines are presented for a quality assessment procedure. Such a predetermined procedure potentially enhances the consistency among different assessors and assessments and facilitates harmonization of assessment procedures. The guidelines are presented in the context of a decision tree with four decision rules for data quality, i.e. 'availability of occupational hygiene information', 'variability and precision issues', 'internal validity' and 'external validity'. These methodological issues are considered to be the most important aspects of data quality and will be discussed in this paper. The decision tree eventually results in three quality classes, i.e. exposure data providing sufficient information, supplementary information and data which should be excluded from the exposure assessment process. The guidelines should not be used in a rigid manner but have to be interpreted in the light of the particular circumstances and purposes of the assessment.

Chemical Industry↗

PubMed1999

Pre-existing medical conditions as predictors of adverse events in day-case surgery.

We have developed mathematical models to estimate the risk of perioperative adverse events in patients with pre-existing conditions undergoing day-case surgery. We studied 17,638 consecutive day-case surgical patients in a prospective study. Preoperative, intraoperative and postoperative data were collected. Risk modelling was performed with backward stepwise multiple logistic regression and validated on a separate subset of our patients. Eighteen pre-existing conditions were entered into the model. We adjusted for age, sex, and duration and type of surgery. Seven associations between pre-existing medical conditions and perioperative adverse events were statistically significant. Hypertension predicted the occurrence of any intraoperative event and intraoperative cardiovascular events. Obesity predicted intraoperative and postoperative respiratory events, and smoking and asthma predicted postoperative respiratory events. Gastro-oesophageal reflux predicted intubation-related events. The presented models of risk estimation were validated internally and provided a useful tool for accurate risk estimation.

Adolescent↗

PubMedDate not supplied

Interpretation and comparison of treatment studies for uncomplicated urinary tract infections in women.

Recent treatment trials for uncomplicated urinary tract infection were reviewed to determine most commonly used methodologic approaches and to assess whether methodologic problems often compromise internal validity and comparability of these studies. The 62 studies surveyed fulfilled an average of 56% (standard deviation, 19.2%) of 12 standards necessary for accurate interpretation and comparability. Standards most often met were: reporting the incidence of adverse-effects (90%); recording presence or absence of pretreatment symptoms (81%); and describing clinical response to therapy (71%). Standards least often met were: having adequate statistical power to detect a meaningful difference between therapies (21%); double-blinded assigning of treatment regimens (37%); and clearly defining criteria for diagnosing cure and failure (35%). Two recurring characteristics that impaired both interpretation of individual studies and comparisons between studies were failure to separately randomize or stratify patients with risk factors known to adversely affect therapeutic response and inadequate description of outcome measures. Consideration of these factors and use of a proposed system for classifying therapeutic outcome in future treatment trials would improve the basis for clinical decision making.

Anti-Bacterial Agents↗

PubMed1990

Statistical aspects of controlled single subject trials.

Randomized controlled trials in groups and single subjects differ in several statistical aspects. In group trials the experimental unit is a randomly selected subject from a predefined population and this subject is randomly assigned to a treatment. Outcome is confined to average effects which can be generalized to the specific population, but which do not necessarily apply to individual persons. In single subject trials the experimental unit is a treatment period and each treatment period is randomly allocated in a multiple cross-over sequence of periods. The single subject is only representative of itself, but similar responses in corresponding single subject trials may justify careful extrapolation of the results. Single subject trials have a high risk of Type II errors. However, the randomization procedure chosen and the type of statistical test applied may enhance the statistical power of such trials. Internal validity depends on modeling the trial design to the clinical features, drug properties and statistical requirements, while reliability is determined by the reproducibility of the trial response.

Humans↗

PubMed2003

Regular visitors are not good substitutes for assessment of elderly patient satisfaction with nursing home care and services.

BACKGROUND: Due to physical and psychological impairments, elderly patients residing in homes are often unable to participate in studies on satisfaction with care services. While their regular visitors provide interesting information, patient-visitor response concordance requires study. Our objective was to measure patient-visitor agreement on quality of care and accommodation. METHODS: A survey was conducted on elderly people in 13 nursing homes and their visitors. The 125 patient-visitor pairs completed the same Nursing Home Satisfaction Questionnaire (NHSQ) independently, for which reliability and internal validity have previously been explored. Satisfaction scores for room comfort, meal provision, information, and medical/nursing care were calculated. To estimate patient-visitor concordance, intraclass coefficients, a bias index, and Pearson's correlation coefficients were calculated. RESULTS: Patient satisfaction scores ranged from 57.8 (information) to 78.6 (room comfort), and visitor satisfaction from 67.9 (meal provision) to 85.9 (medical/nursing care). Mean visitor scores were higher for all scales, with a small-to-moderate index bias statistically significant for medical/nursing care (p <.001), information (p <.001), and meal provision (p =.006). Intraclass correlation coefficients were low for room comfort, information, and medical/nursing care scales (0.08 to 0.18), and nearly acceptable for the meal provision scale (0.46). CONCLUSIONS: Visitors were not able to provide information on elderly patients' satisfaction with nursing home. Their assessments were milder than patient assessments. The NHSQ is reliable for use in either population, but patient and visitor assessments should not be merged in satisfaction studies.

Access to Information↗

PubMed1995

Measurement properties of the Center for Epidemiological Studies Depression Scale: an Australian community study of aged persons.

The measurement properties of the Center for Epidemiological Studies Depression Scale (CES-D) were examined in an Australian community study of aged persons in order to contribute to international validation of the measure. Confirmatory analysis of polychoric correlations was conducted using the generally weighted least squares method. The original four-factor solution proposed by Radloff was successfully replicated for Australians, showing similar underlying structures as for Americans, Canadians, and Japanese. Schmid-Leiman parameterization of the second order factor analysis showed that little information was lost in considering full-scale scores rather than the four subscales separately. The behavior of the CES-D in an Australian population aligns with existing North American research and thus confirms the exceptional functioning of the Well-Being scale in Japan. More work on the behavior of the CES-D in non-English speaking societies is needed to separate issues of wording and grammar from genuine cultural variations. The CES-D was confirmed as essentially unidimensional and robust to minor changes; therefore, it is recommended for use in cross-cultural studies of depression in elderly persons.

Aged↗

PubMed1987

Respiratory questionnaires in occupational studies: their use in multilingual workforces on the Witwatersrand.

The mother tongue of the majority of black workers in the industrial workforces of the Witwatersrand is either Zulu or S Sotho/Tswana, and these are also the main languages spoken in the area. However a substantial minority cite one of several other languages as their mother tongue. In consequence, in occupational surveys using a respiratory questionnaire, the accepted practice has been to use multilingual interviewers who administer the questionnaire in whichever of the two main languages the interviewee requests, but work from an English language version. To test the reproducibility of the information so gathered, a standardized questionnaire was administered to 56 subjects on two occasions approximately three weeks apart by each of two interviewers, one of whose mother tongue was Zulu and the other S Sotho. Reproducibility was little affected by whether the interviewer used her mother tongue or not, pointing to the multilingual competence of both interviewers. Reproducibility was, however, less in subjects not interviewed in their mother tongue compared to those who were. In general, reproducibility was also less for symptom than for history questions, though the phlegm question performed comparably to that reported for more homogeneous language/ethnic groups. Thus, even if internally valid, respiratory symptom information obtained by this method may have limited generalizability. However respiratory history information appears more reliable and may prove of value in the investigation of the natural history of chronic lung disease in this and similar communities.

Adult↗

PubMed1997

Short-term effects of ambient oxidant exposure on mortality: a combined analysis within the APHEA project. Air Pollution and Health: a European Approach.

The Air Pollution and Health: a European Approach (APHEA) project is a coordinated study of the short-term effects of air pollution on mortality and hospital admissions using data from 15 European cities, with a wide range of geographic, sociodemographic, climatic, and air quality patterns. The objective of this paper is to summarize the results of the short-term effects of ambient oxidants on daily deaths from all causes (excluding accidents). Within the APHEA project, six cities spanning Central and Western Europe provided data on daily deaths and NO2 and/or O3 levels. The data were analyzed by each center separately following a standardized methodology to ensure comparability of results. Poisson autoregressive models allowing for overdispersion were fitted. Fixed effects models were used to pool the individual regression coefficients when there was no evidence of heterogeneity among the cities and random effects models otherwise. Factors possibly correlated with heterogeneity were also investigated. Significant positive associations were found between daily deaths and both NO2 and O3. Increases of 50 micrograms/m3 in NO2 (1-hour maximum) or O3 (1-hour maximum) were associated with a 1.3% (95% confidence interval 0.9-1.8) and 2.9% (95% confidence interval 1.0-4.9) increase in the daily number of deaths, respectively. Stratified analysis of NO2 effects by low and high levels of black smoke or O3 showed no significant evidence for an interaction within each city. However, there was a tendency for larger effects of NO2 in cities with higher levels of black smoke. The pooled estimate for the O3 effect was only slightly reduced, whereas the one for NO2 was almost halved (although it remained significant) when two pollutant models including black smoke were applied. The internal validity (consistency across cities) as well as the external validity (similarities with other published studies) of our results on the O3 effect support the hypothesis of a causal relation between O3 and all cause daily mortality. However, the short-term effects of NO2 on mortality may be confounded by other vehicle-derived pollutants. Thus, the issue of independent NO2 effects requires additional investigation.

Europe↗

PubMed1977

Bias due to misclassification in the estimation of relative risk.

Lack of bias in the estimation of relative effect in epidemiologic studies depends on the internal validity of the study. This paper conveys in graphic and tabular form the direction and magnitude of bias due to misclassification of study subjects. A series of computer-generated graphs shows that the departure of the estimate of effect (relative risk or odds ratio) from its true value is a function of sensitivity and specificity (measures of classification validity), disease frequency, and exposure frequency. The discussion of bias emphasizes misclassification of the "outcome" variable; i.e., disease occurrence in a cohort study and exposure rate in a case-control study. Examples are used to illustrate that the magnitude of the bias can be large under circumstances which occur readily in epidemiologic research. When misclassification is equal for the two compared groups, the estimate is biased toward the null value, and in some instances beyond; when differential misclassification occurs (as in selective recall in case-control studies) the bias can be in either direction, and may be great. Formulas are derived to estimate the underlying true value of the relative risk or odds ratio using the investigator's observations together with the estimated sensitivity and specificity of the classification procedure.

Classification↗

PubMed1981

Multiple sclerosis: a two-stage process?

The concept that the pathogenesis of multiple sclerosis (MS) is dependent on both an environmental factor and host factors associated with the puberty period was tested using the data for the Faroe Islands "outbreak." Although this "outbreak" affected only 25 individuals, its value may be unique since it is the only virgin outbreak described. The population affected demonstrated an age-associated bimodality. Incubation period for the older group, using 1942 (midpoint of British troop occupation) as onset time, was 5 years, while for the younger group, using puberty as onset time, a similar 5.7-year incubation period was demonstrated. Male and female incubation periods for both groups were similar, demonstrating an internal validity check. Although 10 cases were below the age of puberty at the time of the occupation, none of these developed disease prior to reaching puberty. The data suggest that onset of pathogensis of MS is dependent on passing or having passed through the puberty period. This would explain why MS is rarely seen below age 10, is unusual below age 15, why age 15 has been a "critical time" in migration studies and why females have an earlier onset than males. The data further indicate that susceptibility to MS may be acquired over a wide range of ages. The fact that many aging curves such as those for estrogen, testosterone or 17-hydroxycorticosteroid show striking similarity to the MS incidence curves raises the question whether infection is the entire explanation for the age distribution.

Adolescent↗

PubMed1984

Nonenzymatic glycosylation of proteins--a new tool for assessment of cumulative hyperglycemia in epidemiologic studies, past and future.

In conclusion, the discovery of nonenzymatic glycosylation of proteins has opened new horizons in all aspects of diabetes management and research. The field is young. Advances in the understanding of the role of this phenomenon in the pathogenesis of diabetic complications and in the quantitating of its occurrence in various bodily proteins, come monthly. The nonenzymatically glycosylated protein markers, because they offer increased internal validity and precision, afford significant advantages over the classical measures of hyperglycemia. By providing improved means of assessing cumulative hyperglycemia, they will contribute to a better understanding of the relationship of diabetes to its chronic complications. They may also lead to an appreciation that mild hyperglycemia plays a substantial causal role in diseases, such as cardiovascular, with which diabetes has been traditionally associated. A variety of nonenzymatically glycosylated proteins exist, applicable to different purposes. Stored sera may well allow their retrospective determination in studies conceived of and/or executed without an appreciation of their potential. It behooves epidemiologists interested in any aspect of diabetes or in diseases for which diabetes is a relevant study factor, to become familiar with the process, measurement, and potential value of nonenzymatic glycosylation of proteins.

Blood Glucose↗

PubMed1995

Community intervention trials: reflections on the Stanford Five-City Project Experience.

In the past two decades several community intervention studies designed to lower the risk of cardiovascular disease in populations have been completed. These trials shared the rationale that the community approach was the best way to address the large population attributable risk of mild elevations of multiple risk factors, the interrelation of several health behaviors, and the potential efficiency of large-scale interventions not limited to the medical care system. These trials also shared several threats to internal validity, especially the small number of intervention units (usually cities) that could be studied. The purpose of this paper is to reflect on the lessons learned in one of the studies, the Stanford Five-City Project, which began in 1978. The anticipated advantages were observed, including the generalizability of the intervention components, the potential for amplification of interventions through diffusion in the community, and the efficiency of the mass media and other community programs for reaching the entire population. Numerous components of the intervention proved effective when evaluated individually, as was true in other community studies. However, the design limitations proved difficult to overcome, especially in the face of unexpectedly large, favorable risk factor changes in control sites. As a result, definitive conclusions about the overall effectiveness of the communitywide efforts were not always possible. Nevertheless, in aggregate, these studies support the effectiveness of communitywide health promotion, and investigators in the field should turn to different questions. The authors have learned how little they know of the determinants of population-level change and the characteristics that separate communities that change quickly in response to general health information from those that do not. Future studies in communities must elucidate these characteristics, while improving the effectiveness of educational interventions and expanding the role of environmental and health policy components of health promotion.

Adult↗

PubMed2003

Randomized controlled trials in evidence-based mental health care: getting the right answer to the right question.

The purpose of clinical research is to answer this question: Would a new treatment, when added to the existing range of treatment options available in practice, help patients? Randomized controlled trials (RCTs)--in particular, double-blind RCTs--have important methodological advantages over observational studies for addressing this question. These advantages, however, come at a price. RCTs compare treatments using a particular allocation rule for assigning patients to treatments (random assignment) that does not mimic real-world practice. "Favorable" results from an RCT indicating that a new treatment is superior to existing treatments are neither necessary nor sufficient for establishing a "yes" answer to the question posed above. Modeled on an experimental design, RCTs are expensive in time and money and must compare simple differences in treatments. Findings have a high internal validity but may not address the needs of the field, particularly where treatment is complex and rapidly evolving. Design of clinical research needs to take account of the way treatments are allocated in actual practice and include flexible designs to answer important questions most effectively.

Evidence-Based Medicine↗