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 1,045 records · Page 58Linked to original sources

PubMed1993

Prognostic index for recurrence of seizures after remission of epilepsy. Medical Research Council Antiepileptic Drug Withdrawal Study Group.

OBJECTIVES: To develop and test a prognostic index for the recurrence of seizures after a minimum remission of seizures of two years in people with a history of epilepsy. DESIGN: Information from a large prospective randomised study of withdrawal of antiepileptic drugs was used to identify clinical and treatment factors of prognostic importance in determining the recurrence of seizures. A split sample approach was used to test the internal validity of predictions made on the basis of identified prognostic factors. SETTING: Centres in six European countries. MAIN OUTCOME MEASURES: Comparison of predicted and observed rates of recurrence of seizure. SUBJECTS: 1013 patients randomised to the Medical Research Council study for antiepileptic drug withdrawal. RESULTS: The Cox proportional hazards model identified several factors that increased the risk of seizures recurring. These included being 16 years or older; taking more than one antiepileptic drug; experiencing seizures after starting antiepileptic drug treatment; a history of primary or secondarily generalised tonic-clonic seizures; a history of myoclonic seizures; and having an abnormal electroencephalogram. The risks of seizures recurring decreased with increasing time without seizures. The model allowed estimation of the risk of seizures recurring in the next one and two years under the policies of continued antiepileptic drug treatment and slow withdrawal of drugs. Split sample validation suggested that the model was well calibrated. CONCLUSION: The model is currently the best available aid for counselling the many patients in the community with epilepsy currently in remission who seek advice about the risks of seizures recurring if they stop antiepileptic drug treatment. The model requires validation in a broad population of patients, and such studies are in progress.

Age Factors↗

PubMed1999

Association between selective serotonin reuptake inhibitors and upper gastrointestinal bleeding: population based case-control study.

OBJECTIVE: To examine the association between selective serotonin reuptake inhibitors and risk of upper gastrointestinal bleeding. DESIGN: Population based case-control study. SETTING: General practices included in the UK general practice research database. SUBJECTS: 1651 incident cases of upper gastrointestinal bleeding and 248 cases of ulcer perforation among patients aged 40 to 79 years between April 1993 and September 1997, and 10 000 controls matched for age, sex, and year that the case was identified. INTERVENTIONS: Review of computer profiles for all potential cases, and an internal validation study to confirm the accuracy of the diagnosis on the basis of the computerised information. MAIN OUTCOME MEASURES: Current use of selective serotonin reuptake inhibitors or other antidepressants within 30 days before the index date. RESULTS: Current exposure to selective serotonin reuptake inhibitors was identified in 3.1% (52 of 1651) of patients with upper gastrointestinal bleeding but only 1.0% (95 of 10 000) of controls, giving an adjusted rate ratio of 3.0 (95% confidence interval 2.1 to 4.4). This effect measure was not modified by sex, age, dose, or treatment duration. A crude incidence of 1 case per 8000 prescriptions was estimated. A small association was found with non-selective serotonin reuptake inhibitors (relative risk 1.4, 1.1 to 1.9) but not with antidepressants lacking this inhibitory effect. None of the groups of antidepressants was associated with ulcer perforation. The concurrent use of selective serotonin reuptake inhibitors with non-steroidal anti-inflammatory drugs increased the risk of upper gastrointestinal bleeding beyond the sum of their independent effects (15.6, 6.6 to 36.6). A smaller interaction was also found between selective serotonin reuptake inhibitors and low dose aspirin (7.2, 3.1 to 17.1). CONCLUSIONS: Selective serotonin reuptake inhibitors increase the risk of upper gastrointestinal bleeding. The absolute effect is, however, moderate and about equivalent to low dose ibuprofen. The concurrent use of non-steroidal anti-inflammatory drugs or aspirin with selective serotonin reuptake inhibitors greatly increases the risk of upper gastrointestinal bleeding.

Adult↗

PubMed2003

Evidence for risk of bias in cluster randomised trials: review of recent trials published in three general medical journals.

OBJECTIVE: To examine the prevalence of a risk of bias associated with the design and conduct of cluster randomised controlled trials among a sample of recently published studies. DESIGN: Retrospective review of cluster randomised trials published in the BMJ, Lancet, and New England Journal of Medicine from January 1997 to October 2002. MAIN OUTCOME MEASURES: Prevalence of secure randomisation of clusters, identification of participants before randomisation (to avoid foreknowledge of allocation), differential recruitment between treatment arms, differential application of inclusion and exclusion criteria, and differential attrition. RESULTS: Of the 36 trials identified, 24 were published in the BMJ,11 in the Lancet, and a single trial in the New England Journal of Medicine. At the cluster level, 15 (42%) trials provided evidence for secure allocation and 25 (69%) used stratified allocation. Few trials showed evidence of imbalance at the cluster level. However, some evidence of susceptibility to risk of bias at the individual level existed in 14 (39%) studies. CONCLUSIONS: Some recently published cluster randomised trials may not have taken adequate precautions to guard against threats to the internal validity of their design.

Bias↗

PubMed2005

Proposal of a new prognostic model for hepatocellular carcinoma: an analysis of 403 patients.

BACKGROUND: The prognosis of hepatocellular carcinoma (HCC) is highly dependent on tumour extension and liver function. Recently, two new prognostic scoring systems-the CLIP score, developed by Italian investigators and the BCLC score, developed in Barcelona-have been widely used to assess prognosis in patients presenting with hepatocellular carcinoma. Each system has its own relative limitations. AIMS: To create a new prognostic scoring system which is simple, easy to calculate, and suitable for estimating prognosis during radical treatment of early HCC. METHODS: A total of 403 consecutive patients with HCC treated by percutaneous ablation at the Department of Gastroenterology, University of Tokyo Hospital, between 1990 and 1997 were used as the training sample to identify prognostic factors for our patients and used to develop the Tokyo score. As a testing sample, 203 independent patients who underwent hepatectomy at the Department of Hepato-Biliary-Pancreatic Surgery were studied. Prognostic factors were analysed by univariate and multivariate Cox proportional hazard regression. RESULTS: The Tokyo score consists of four factors: serum albumin, bilirubin, and size and number of tumours. Five year survival was 78.7%, 62.1%, 40.0%, 27.7%, and 14.3% for Tokyo scores 0, 1, 2, 3, and 4-6, respectively. The discriminatory ability of the Tokyo score was internally validated by bootstrap methods. The Tokyo score, CLIP score, and BCLC staging were compared by Akaike information criterion and Harrell's c index among training and testing samples. In the testing sample, the predictive ability of the Tokyo score was equal to CLIP and better than BCLC staging. CONCLUSIONS: The Tokyo score is a simple system which provides good prediction of prognosis for Japanese patients with HCC requiring radical therapy.

Adolescent↗

PubMed2005

Multivariate prediction of major adverse cardiac events after 9914 percutaneous coronary interventions in the north west of England.

OBJECTIVE: To develop a multivariate prediction model for major adverse cardiac events (MACE) after percutaneous coronary interventions (PCIs) by using the North West Quality Improvement Programme in Cardiac Interventions (NWQIP) PCI Registry. SETTING: All NHS centres undertaking adult PCIs in north west England. METHODS: Retrospective analysis of prospectively collected data on 9914 consecutive patients undergoing adult PCI between 1 August 2001 and 31 December 2003. A multivariate logistic regression analysis was undertaken, with the forward stepwise technique, to identify independent risk factors for MACE. The area under the receiver operating characteristic (ROC) curve and the Hosmer-Lemeshow goodness of fit statistic were calculated to assess the performance and calibration of the model, respectively. The statistical model was internally validated by using the technique of bootstrap resampling. MAIN OUTCOME MEASURES: MACE, which were in-hospital mortality, Q wave myocardial infarction, emergency coronary artery bypass graft surgery, and cerebrovascular accidents. RESULTS: Independent variables identified with an increased risk of developing MACE were advanced age, female sex, cerebrovascular disease, cardiogenic shock, priority, and treatment of the left main stem or graft lesions during PCI. The ROC curve for the predicted probability of MACE was 0.76, indicating a good discrimination power. The prediction equation was well calibrated, predicting well at all levels of risk. Bootstrapping showed that estimates were stable. CONCLUSIONS: A contemporaneous multivariate prediction model for MACE after PCI was developed. The NWQIP tool allows calculation of the risk of MACE permitting meaningful risk adjusted comparisons of performance between hospitals and operators.

Adult↗

PubMed2003

Routine narrative analysis as a screening tool to improve data quality.

AIM: To determine whether narrative information in emergency department surveillance systems can be systematically interrogated to improve our understanding of the causes of injury. METHODS: Screening algorithms for location, intent, and activity were developed from structured analysis of narrative data from 98999 records. The algorithms were then tested on a 50000 record database containing entries in both of the two narrative fields. A proxy gold standard was defined as the total extract using both code and narrative. Sensitivity and specificity of the emergency department coding and narrative algorithms was calculated. RESULTS: The proportion of records carrying an informative emergency department code was higher in records containing narrative-the percentage of causes coded "not know" dropped by 28.3%. The sensitivity of coded data varied from 42% to 98 % and from 33% to 99% for narrative data. Narrative analysis increased the percentage of home injuries identified by 19%, assaults by 26%, and rugby injuries by 137%. CONCLUSIONS: Using a small amount of narrative is a practical and effective means of developing more informative injury causation data in an emergency department based surveillance system. It allows for internal validation of the codes and for the identification of emerging hazards without adding more "tick boxes" or further burdening data entry clerks.

Algorithms↗

PubMed2004

Bias.

The concept of bias is the lack of internal validity or incorrect assessment of the association between an exposure and an effect in the target population in which the statistic estimated has an expectation that does not equal the true value. Biases can be classified by the research stage in which they occur or by the direction of change in a estimate. The most important biases are those produced in the definition and selection of the study population, data collection, and the association between different determinants of an effect in the population. A definition of the most common biases occurring in these stages is given.

Bias↗

PubMed2006

The effect of visual training for patients with visual field defects due to brain damage: a systematic review.

The objective of this review was to evaluate whether systematic visual training leads to (1) a restitution of the visual field (restoration), (2) an increase in the visual search field size or an improvement in scanning strategies (compensation) and (3) a transfer of training-related improvements in activities of daily living such as reading. To retrieve relevant publications, computer-aided searches of databases (Medline, Embase, Cinahl, Cochrane Central Registers of Controlled Trials) and extensive reference tracing and hand searching were performed. Subsequently, all retrieved and blinded studies were scored on methodological quality. 14 studies were included, 2 randomised controlled trials (RCTs) and 12 within-subject repeated-measures designs (RMD). One of the two RCT studies had good quality. The internal validity of the RMD studies varied from poor to good. Five studies reported a significant effect of the vision restoration therapy (VRT), whereas two studies reported no effect using scanning laser ophthalmoscopy or Goldmann perimetry as outcome measure. All authors of the studies on scanning compensatory therapy (SCT) found a significant effect of up to 30 degrees visual search field, a significant increase in reading speed or decrease in reading errors. It is unclear to what extent patients benefit from restoration therapy in relation to a more efficient scanning strategy which enables them to read faster or to avoid obstacles in a better way. No study has given a satisfactory answer. SCT seems to provide a more successful rehabilitation with more simple and user-friendly training techniques. Validated questionnaires provide the most reliable subjective data to assess the transfer of the relevance of training procedures to activities of daily living of the patient. Hence, SCT is recommended until the effect of the VRT is defined.

Brain Diseases↗

PubMed2001

Effect of experience of severe stroke on subjective valuations of quality of life after stroke.

Previous work suggests that the quality of life associated with severe disability after stroke is rated very poorly by members of the public, often as being worse than death. Other evidence suggests that experience of illness alters perceptions of its severity. This was tested for severe stroke. Eleven patients with severely disabling stroke, but able to complete a standard gamble interview, 22 age and sex matched controls, and 20 health professionals participated. A standard gamble interview was carried out to determine the quality of life (utility) associated with three hypothetical scenarios representing mild, moderate, and severe stroke, and current health. A sample was retested for reliability, and comparisons were made with other measures of health status. All three subject groups showed wide variation in the utilities they attached to each of the scenarios. The control subjects' valuations were lower than those of either patients or staff members, especially for moderate stroke (median 0.30, 0.73, and 0.68 respectively). There were weak to moderate correlations between utilities and other measures of health status including the Barthel index (r=0.51) and Rivermead mobility score (r=0.24). Test retest-reliability was modest (reliability coefficient 0.75), but indicators of the internal validity of the results were good. In conclusion, it cannot be assumed that general population valuations are valid for patient groups. In clinical practice it is unsafe to make any assumption about subjective quality of life after stroke, due to the wide range of valuations given, although many people rate severe and moderate stroke at least as bad as death.

Aged↗

PubMed1997

A systematic review of controlled clinical trials on the prevention of back pain in industry.

OBJECTIVE: To assess the effectiveness of lumbar supports, education, and exercise in the prevention of back pain in industry. METHODS: A computerised search for controlled clinical trials was conducted. A criteria list was used to assess the methodological quality of the studies. The available evidence for the effectiveness of the interventions was graded with a rating system for the level of evidence. Effect sizes of individual studies were combined if the studies were sufficiently similar. RESULTS: 11 studies were identified for the review. The methodological quality of all studies was low, with a maximum score of three out of seven for internal validity. There was no evidence for the effectiveness of lumbar supports due to contradictory outcomes of the studies. Five of the six studies on education reported no effect. Thus there is limited evidence that education does not help to prevent back pain. All three studies on exercise reported a positive result, indicating limited evidence for the effectiveness of exercise. The combined effect size for exercise was 0.53, which is a medium sized effect. CONCLUSIONS: Although widely used, there is little evaluative research on the preventive measures studied here. The review showed that there is limited evidence that exercise has some effect in the prevention of back pain and that education is not effective. No conclusive evidence was found for or against the effectiveness of lumbar supports. Research of higher methodological quality is needed before firm conclusions on the effectiveness of lumbar supports, education, and exercise in the prevention of back pain in industry can be drawn.

Back Pain↗

PubMed2005

Genetic variation and willingness to participate in epidemiologic research: data from three studies.

The differences in common genetic polymorphism frequencies by willingness to participate in epidemiologic studies are unexplored, but the same threats to internal validity operate as for studies with nongenetic information. We analyzed single nucleotide polymorphism genotypes, haplotypes, and short tandem repeats among control groups from three studies with different recruitment designs that included early, late, and never questionnaire responders, one or more participation incentives, and blood or buccal DNA collection. Among 2,955 individuals, we compared 108 genotypes, 8 haplotypes, and 9 to 15 short tandem repeats by respondent type. Among our main comparisons, single nucleotide polymorphism genotype frequencies differed significantly (P < 0.05) between respondent groups in six instances, with 13 expected by chance alone. When comparing the odds of carrying a variant among the various response groups, 19 odds ratios were </=0.70 or >/=1.40, levels that might be notably different. Among the various respondent group comparisons, haplotype and short tandem repeat frequencies were not significantly different by willingness to participate. We observed little evidence to suggest that genotype differences underlie response characteristics in molecular epidemiologic studies, but a greater variety of genes should be examined, including those related to behavioral traits potentially associated with willingness to participate. To the extent possible, investigators should evaluate their own genetic data for bias in response categories.

Community Participation↗

PubMed2006

Nomograms provide improved accuracy for predicting survival after radical cystectomy.

AIMS: To develop multivariate nomograms that determine the probabilities of all-cause and bladder cancer-specific survival after radical cystectomy and to compare their predictive accuracy to that of American Joint Committee on Cancer (AJCC) staging. METHODS: We used Cox proportional hazards regression analyses to model variables of 731 consecutive patients treated with radical cystectomy and bilateral pelvic lymphadenectomy for bladder transitional cell carcinoma. Variables included age of patient, gender, pathologic stage (pT), pathologic grade, carcinoma in situ, lymphovascular invasion (LVI), lymph node status (pN), neoadjuvant chemotherapy (NACH), adjuvant chemotherapy (ACH), and adjuvant external beam radiotherapy (AXRT). Two hundred bootstrap resamples were used to reduce overfit bias and for internal validation. RESULTS: During a mean follow-up of 36.4 months, 290 of 731 (39.7%) patients died; 196 of 290 patients (67.6%) died of bladder cancer. Actuarial all-cause survival estimates were 56.3% [95% confidence interval (95% CI), 51.8-60.6%] and 42.9% (95% CI, 37.3-48.4%) at 5 and 8 years after cystectomy, respectively. Actuarial cancer-specific survival estimates were 67.3% (62.9-71.3%) and 58.7% (52.7-64.2%) at 5 and 8 years, respectively. The accuracy of a nomogram for prediction of all-cause survival (0.732) that included patient age, pT, pN, LVI, NACH, ACH, and AXRT was significantly superior (P=0.001) to that of AJCC staging-based risk grouping (0.615). Similarly, the accuracy of a nomogram for prediction of cancer-specific survival that included pT, pN, LVI, NACH, and AXRT (0.791) was significantly superior (P=0.001) to that of AJCC staging-based risk grouping (0.663). CONCLUSIONS: Multivariate nomograms provide a more accurate and relevant individualized prediction of survival after cystectomy compared with conventional prediction models, thereby allowing for improved patient counseling and treatment selection.

Adult↗

PubMedDate not supplied

Evaluation of the German version of the PTSD Symptom Scale (PSS).

The psychometric properties of the PTSD Symptom Scale (PSS) were evaluated in a clinical sample of severely injured in-patients after a traffic accident (n = 123). The PSS contains 17 items which were derived from the DSM-III-R criteria of posttraumatic stress disorder (PTSD). The results indicate that the PSS has satisfactory reliability and validity (internal and external). The results are in correspondence with the results of Foa et al. using a sample of rape and non-sexual-assault patients.

Accidents, Traffic↗

PubMed2001

Importance of individual response in symptom score evaluation.

In making treatment decisions for patients with benign prostatic hyperplasia (BPH), physicians have to rely on the efficacy data published in the literature and adapt this to individual patient's needs. Criticism can be made, however, of the randomised clinical trials (RCTs) that are performed, as the patients enrolled are not an adequate reflection of the general patient population. Although internal validity is high in RCTs with regard to inclusion criteria, external validity is reduced. Another failing of RCTs is the way in which patients are assessed. Typically in many studies, symptom improvement is expressed as a percentage of the Symptom Index improvement. This can be misleading if the results of two trials are compared as this value depends on the pre-treatment Symptom Index. Other methods of evaluation should be considered, such as the presentation of direct symptom outcomes (threshold improvement), the cumulative frequency distribution of threshold improvements or linear regression analysis of individual IPSS. All of these means of expressing the results focus clinical evaluation on the patient himself.

Clinical Trials as Topic↗

PubMed2001

[Distant healing and clinical research].

Distant healing is one of the most controversially discussed methods of complementary medicine. In the first section this paper outlines the history of spiritual healing and describes some possible definitions and different methods of spiritual healing. Based on a literature search in Medline, EMBASE, Current Contents, Allied and Complementary Medicine Database (AMED) as well as a manual tracking, current distant healing studies (excluding therapeutic touch studies) (n = 16) and some review articles (n = 6) are outlined in the second section. In addition, the randomized clinical double-blind studies (n = 12) are judged as to their formal quality by means of the Jadad Scale and the Internal Validity Scale (IV). Based on the controversially discussed study by Harris et al., some discussion points in the research field of spiritual healing are presented in the third section of this paper. From the evidence contained in the studies of this review article, no firm conclusions about the efficacy or inefficacy of healing can yet be made.

Complementary Therapies↗

PubMed2006

Prevalence of epilepsy in a rural district of central Lao PDR.

PURPOSE: To assess the prevalence of epilepsy in a rural district of Lao PDR and to describe the clinical and epidemiological profile of the disease. METHODS: Door-to-door screening was performed on the entire population of 8 randomly selected villages in the Hinheub district, using an internationally validated and standardized questionnaire. Additional passive case detection was performed through village key informants. Suspected epilepsy patients identified by the questionnaire were revisited and examined by an experienced neurologist on two follow-up visits. The confirmation of epilepsy was based only on an in-depth clinical examination. Electroencephalograms were performed at the district health care center. RESULTS: In the 8 villages, 277 suspected cases of epilepsy were identified among 4,310 interviewed subjects; 194 of whom (70%) underwent a clinical examination by a neurologist during the first visit while 65 of 83 remaining suspected cases were seen on the second confirmation visit. Twenty-seven persons with epilepsy were identified. Six additional patients were diagnosed in 219 self-referred subjects. An overall prevalence of 7.7 cases of epilepsy per thousand inhabitants was calculated (95% CI 5.3-10.7). Generalized epilepsy (21 cases, 63.6%) was commoner than partial epilepsy (9 cases, 27.3%). The remaining 3 cases (9.1%) were not-classifiable as either generalized or partial. EEG abnormal findings were found in 12 of the 24 patients (50.0%) who had an EEG registration. CONCLUSIONS: This is the first study in Lao PDR to estimate the prevalence of epilepsy. Compared to Western countries it shows a pattern towards a higher prevalence.

Adolescent↗

PubMed1990

A dimensional approach to severe delusional psychoses.

By use of latent trait models a 7-item rating scale of severe delusional psychoses was established based on the PSE interview. Data from 88 first-admitted patients with delusional psychoses were analysed. These data assigned good internal validity of the scale and revealed a dimensional rather than a categorical distribution of severe delusional psychoses. Using schizophrenia as a reference, the scale with a cut-off point greater than or equal to 1 established the diagnosis with a sensitivity of 0.84 and a specificity of 0.95. In a study to come a latent class analysis among deluded patients will be performed.

Delusions↗

PubMed2004

Relationship between erectile dysfunction and silent myocardial ischemia in apparently uncomplicated type 2 diabetic patients.

BACKGROUND: Erectile dysfunction (ED) is associated with coronary artery disease (CAD). In diabetic patients, CAD is often silent. Among diabetic patients with silent CAD, the prevalence of ED has never been evaluated. We investigated whether ED is associated with asymptomatic CAD in type 2 diabetic patients. METHODS AND RESULTS: We evaluated the prevalence of ED in 133 uncomplicated diabetic men with angiographically verified silent CAD and in 127 diabetic men without myocardial ischemia at exercise ECG, 48-hour ambulatory ECG, and stress echocardiography. The groups were comparable for age and diabetes duration. Patients were screened for ED using the validated International Index of Erectile Function (IIEF-5) questionnaire. The prevalence of ED was significantly higher in patients with than in those without silent CAD (33.8% versus 4.7%; P=0.000). Multiple logistic regression analysis showed that ED, apolipoprotein(a) polymorphism, smoking, microalbuminuria, HDL, and LDL were significantly associated with silent CAD; among these risk factors, ED appeared to be the most efficient predictor of silent CAD (OR, 14.8; 95% CI, 3.8 to 56.9). CONCLUSIONS: Our study first shows a strong and independent association between ED and silent CAD in apparently uncomplicated type 2 diabetic patients. If our findings are confirmed, ED may become a potential marker to identify diabetic patients to screen for silent CAD. Moreover, the high prevalence of ED among diabetics with silent CAD suggests the need to perform an exercise ECG before starting a treatment for ED, especially in patients with additional cardiovascular risk factors.

Coronary Artery Disease↗