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Results for “Validation Study”

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PubMed1988

Relation of monophasic action potential recorded with contact electrode to underlying transmembrane action potential properties in isolated cardiac tissues: a systematic microelectrode validation study.

Monophasic action potentials, recorded with contact non-suction electrodes, have been used both clinically and experimentally. However, to date no systematic microelectrode validation studies have been done to underlying myocardial cell populations from different myocardial regions with different transmembrane potential profiles. In the present study transmembrane action potential properties, recorded with standard microelectrodes, were compared with monophasic action potentials recorded with contact electrodes in three different (endocardium, epicardium, and free running Purkinje fibre) isolated canine preparations during pacing and during spontaneous automatic activity. The mean transmembrane durations at 50% and 90% repolarisations (APD50 and APD90) of 19-30 cells at a monophasic action potential recording site was not statistically significant from monophasic action potential duration in all three tissue preparations studied. However, in endocardial preparations, composed of superficial (1-2 cell layers) Purkinje fibres with deeper ventricular muscle cells, the APD50 (139(17) ms) and APD90 (181(26) ms) of monophasic action potentials more closely reflected (but not significantly different) the underlying deeper ventricular muscle cells (APD50 134(14) ms and APD90 167(15) ms) rather than the mean transmembrane action potential durations of the underlying most superficial Purkinje fibres (166(22) ms for APD50 and 210(30) ms for APD90) (p less than 0.025). Tetrodotoxin (TTX) at 1 x 10(-6) mol.litre-1 shortened Purkinje fibre action potential duration and slightly lengthened that of ventricular muscle. Simultaneously recorded monophasic action potential showed an intermediate change in action potential duration. Incremental pacing and applied single premature stimuli resulted in similar degrees of shortening of action potential duration for both monophasic action potential and transmembrane potential in all three preparations. In endocardial preparations, barium chloride (4 mmol.litre-1) superfusion induced early afterdepolarisations, and spontaneous phase 4 depolarisations (n = 6) in both Purkinje and ventricular muscle cells giving rise to spontaneous automatic activity. These abnormal automatic activities were accurately detected by simultaneous monophasic action potential recordings. Suppression of automaticity by verapamil (0.2-0.5 micrograms.ml-1) as confirmed by transmembrane action potential recordings were similarly detected by monophasic action potential recordings (ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗

PubMed1994

A two-stage validation study for determining sensitivity and specificity.

A two-stage procedure for estimating sensitivity and specificity is described. The procedure is developed in the context of a validation study for self-reported atypical nevi, a potentially useful measure in the study of risk factors for malignant melanoma. The first stage consists of a sample of N individuals classified only by the test measure. The second stage is a subsample of size m, stratified according the information collected in the first stage, in which the presence of atypical nevi is determined by clinical examination. Using missing data methods for contingency tables, maximum likelihood estimators for the joint distribution of the test measure and the "gold standard" clinical evaluation are presented, along with efficient estimators for the sensitivity and specificity. Asymptotic coefficients of variation are computed to compare alternative sampling strategies for the second stage.

Adult↗

PubMed1989

A computer-based interview system for patients with back pain. A validation study.

A microcomputer-based system has been designed to interview patients with a view to investigating and establishing common syndromes of back and leg pain. In a randomized crossover validation study, 50 consecutive outpatients were interviewed by the computer and had a conventional clerking by a doctor. The conventional clerking made minor errors in 3.75% of questions answered and major errors in 0.90%. The computer made minor errors in 6.75% of questions and major errors in 5.45%. The majority of the computer errors were due to inadequate question design. These have been corrected, and it is anticipated that the computer will now have an overall rate of 94% correct answers and be sufficiently accurate to pursue the aim of clinical syndrome identification.

Back Pain↗

PubMed1995

Ecological measures of cognitive functioning: a validation study.

Observed cognitive decline in the elderly has been widely reported in the literature. The relation of experimental cognitive ability measures to real-world cognitive competence has been questioned. This research examines the validity of English-language versions of two measures of everyday competency: the Memory in Reality test involving object placement recall and the Coin Test, a money-sorting task. The measures were developed as part of a Swedish epidemiologic study. Validity was evaluated by comparison of these tasks with standard cognitive tests and with a measure of metamemory. It was expected that the ecological measures would have a stronger association with metamemory than the standard tests. Subjects were 93 community-dwelling women, aged 75 and older. The ecological tasks correlated positively with the standard tests, but there were inconsistent relations of both standard and ecological measures with metamemory. The results partly support use of these measures for evaluating everyday functioning.

Activities of Daily Living↗

PubMed1996

Development of a predictive model for growth of Listeria monocytogenes in a skim milk medium and validation studies in a range of dairy products.

A predictive model based on growth of Listeria monocytogenes in milk is described. The main aim of this work was to generate a predictive model in milk acidified with lactic acid to mimic conditions found in a range of dairy products. A complete factorial design was employed to determine the effects of pH (4.5-7.5), temperature (3-35 degrees C) and salt concentration (0-8%) on growth of the organism. There were 210 design points and growth curves were individually fitted for the Gompertz function using non-linear regression. Descriptors of the curves, such as lag phase duration (LPD), exponential growth rate (EGR) and generation time (GT) were calculated and polynomial models were developed relating these to pH, temperature and salt concentration. The selected cubic polynomial model gave acceptable predictive estimates of growth and was stable, i.e. predictions were repeatable over the range of environmental variables studied. The model was further tested to determine its capacity for predicting growth of listeria in a range of dairy foods and these validation studies confirm its usefulness as a rapid means of estimating growth of the organism under specified environmental conditions.

Animals↗

PubMed1989

An external validity study of the MMPI Personality Disorder Scales.

This study examined the external validity of the MMPI Personality Disorder (PD) scales. Patients diagnosed with personality disorders (n = 23), according to a structured interview, were contrasted with medical control subjects and psychiatric patients with no personality disorder (n = 33). The MMPI PD scales could discriminate patients with any personality disorder and patients with specific clusters of personality disorders. Convergent validity was demonstrated by high correlations between the MMPI PD scales and the comparable Millon Clinical Multiaxial Inventory scales, as well as the number of DSM-III personality disorder symptoms. This study represents a preliminary step in the external validation of the MMPI PD scales.

Adult↗

PubMed1994

Measurement of shoulder related disability: results of a validation study.

OBJECTIVE: To develop and validate a questionnaire to quantify disability associated with shoulder symptoms. METHODS: A set of questions relevant to shoulder symptoms from a general disability interview was developed and the questionnaire applied to a cross-sectional population survey and a prospective study of general practice attenders. Subjects included adults who reported current shoulder pain in a population survey and patients from three general practices who attended with shoulder symptoms during a six month period. The main outcome measures were: frequency of problems with daily living related to shoulder symptoms, total score on 22-item disability questionnaire, and measures of shoulder movement. RESULTS: A higher proportion (80%) of patients attending their general practitioner with shoulder symptoms had five or more disabilities compared with subjects reporting shoulder pain in a community survey (34%). The ranked frequency with which each disability was reported was similar in the two groups, although sleep disturbance was the most common problem in consulters. Self-reported disability is correlated with measures of restricted shoulder movement. CONCLUSION: This disability questionnaire was simple to complete and should prove useful for both general practice and population-based studies of shoulder pain.

Activities of Daily Living↗

PubMed1989

Conners' Teacher's Rating Scale--a validity study in Hong Kong.

The validity of the Conners' teacher's rating scale (CTRS) in Hong Kong Chinese school children was examined. It was found that CTRS could significantly differentiate a behaviorally deviant group and the normal population; that CTRS has a strong positive correlation with the teacher's decision to refer a child to a mental health professional; that the CTRS by itself is not useful as a diagnostic instrument; and finally, it cannot stand alone as a screening instrument in the epidemiological study of childhood hyperactivity.

Attention Deficit Disorder with Hyperactivity↗

PubMedDate not supplied

International validation study for the determination of chloramphenicol in bovine muscle.

A gas chromatographic (GC) procedure for the quantitation and GC/negative ion chemical ionization mass spectrometric (NICIMS) confirmation of chloramphenicol in calf muscle tissue was the subject of a validation study. Five analysts representing 5 laboratories in 4 countries participated in the quantitative method and analyzed 7 randomly numbered blind triplicates at 4 fortified and 3 incurred tissue concentrations on 3 separate days. The chloramphenicol concentrations ranged from 0 to 2.5 ppb. All data were reported to 3 significant figures. The coefficients of variation were 9.5-28.7% for repeatability and 14.6-38% over the study range for reproducibility. NICIMS data representing 3 laboratories in 3 countries successfully confirmed chloramphenicol in samples at 0.6 ppb or greater with no false positives in blank tissues.

Animals↗

PubMed1994

Accuracy and precision of quantitative arteriography in the evaluation of coronary artery disease after coronary bypass surgery. A validation study.

Computer-assisted quantitative coronary arteriography (QCA) has gained widespread acceptance in assessing changes in coronary dimensions over time, but little is known about the utility of QCA in patients having undergone coronary bypass surgery. As a validation study, we analyzed the accuracy and precision of QCA in a subset of the baseline angiograms of a clinical trial in 395 post-bypass men with low HDL cholesterol concentrations who have been randomized to receive double-blind gemfibrozil or placebo for 2 1/2 years. Based on repeat measurements of the same cineframe, the average diameter of a segment (ADS) had a mean coefficient of variation (CV) of 3.1%. The mean CVs of the minimum luminal diameter (MLD), percent diameter stenosis (PDS) and stenotic flow reserve of an obstruction were 8.6, 10.2 and 9.8%, respectively, but the area of the atherosclerotic plaque had an unacceptably high CV, 24.0%. When the measurements from two contrast injections into a native coronary artery during the same angiographic session were compared, precision (standard deviation of the differences) was 0.198 mm for ADS, 0.192 mm for MLD, and 7.37% for PDS. Variability was not substantially reduced when measurements from 3 or 5 consecutive cineframes were averaged. Comparable repeatability was found when venous bypass grafts were imaged twice, whether the grafts themselves or the grafted native vessels were analyzed. We conclude that QCA has an acceptable accuracy and precision in analyzing coronary dimensions in bypass-grafted patients. A change of 0.40 mm in ADS and MLD, and 20% in PDS represent true progression or regression of coronary atherosclerosis with more than 95% confidence.

Cholesterol, HDL↗

PubMed1993

Localisation of cerebral function using topographical mapping of EEG: a preliminary validation study.

In an attempt to validate the use of topographical mapping of EEG as a method of localising cerebral function, EEG was recorded during a simple motor task. A minimum of 20 sec artifact-free EEG was recorded from 24 healthy right handed subjects in each of 4 conditions: eyes open 1, motor task (left/right, order randomized), eyes open 2. EEG amplitude maps were computed in delta, theta, alpha, and beta (1 and 2). Differences were seen between the eyes open and the motor conditions in alpha, beta 1 and beta 2 localised to the motor and supplementary motor areas. It is argued that topographical mapping of EEG is a valid method of localising cognitive function in healthy individuals for the Luria task.

Adult↗

PubMed1995

Acute Physiology and Chronic Health Evaluation II scoring system in acute myocardial infarction: a prospective validation study.

OBJECTIVE: To study the usefulness of the Acute Physiology and Chronic Health Evaluation II (APACHE II) scoring system for prognostication of inhospital mortality in acute myocardial infarction. DESIGN: A prospective validation study. SETTING: A medical intensive care unit (ICU) at a university hospital. PATIENTS: Over a 3-yr period, 2,007 admissions of 1,714 patients with acute myocardial infarction were studied. In readmissions to the medical ICU during the same hospital stay, only the first admission was studied. MEASUREMENTS AND MAIN RESULTS: Mean age of the patients was 72 +/- 10 yrs. The medical ICU mortality rate was 13% and total hospital mortality rate was 16%. Mean APACHE II score was 11.6 +/- 6.5. There was a close correlation between observed and predicted mortality rates in classes of patients with various APACHE II scores. Observed mortality in patients with scores of 20 to 24 was higher than the predicted mortality (p < .03). In this subgroup, 25% of the patients had a length of stay in the medical ICU of < 8 hrs. CONCLUSIONS: Inhospital mortality in patients with acute myocardial infarction could be accurately predicted with APACHE II scores. Prognostication was not as good in patients with a length of stay in the medical ICU of < 8 hrs.

APACHE↗

PubMedDate not supplied

Multiresidue gas chromatographic method for determining organochlorine pesticides in meats: validation study for swine and beef fats.

A validation of a previously studied method for determining organochlorine residues in poultry fat was conducted to extend the usefulness of the method to beef and swine fats. The validation samples consisted of 16 materials all analyzed in duplicate. Fortification levels ranged from 0.02 to 1.2 ppm for alpha-BHC, lindane, cis- and trans-chlordane, octachlor epoxide, o,p'- and p,p'-DDT, p,p'-DDE, p,p'-TDE, hexachlorobenzene, heptachlor epoxide, dieldrin, endrin, methoxychlor, mirex, and toxaphene. The average recovery was 101% with a range of 79-113%, not including toxaphene. The ranges of coefficients of variation were CVo = 0-23.37% and CVx = 3.74-26.19%. The results were comparable to the previous collaborative study of the same method for poultry fat. The extended method has been adopted official first action.

Animals↗

PubMed1996

Algorithms for verbal autopsies: a validation study in Kenyan children.

The verbal autopsy (VA) questionnaire is a widely used method for collecting information on cause-specific mortality where the medical certification of deaths in childhood is incomplete. This paper discusses review by physicians and expert algorithms as approaches to ascribing cause of deaths from the VA questionnaire and proposes an alternative, data-derived approach. In this validation study, the relatives of 295 children who had died in hospital were interviewed using a VA questionnaire. The children were assigned causes of death using data-derived algorithms obtained under logistic regression and using expert algorithms. For most causes of death, the data-derived algorithms and expert algorithms yielded similar levels of diagnostic accuracy. However, a data-derived algorithm for malaria gave a sensitivity of 71% (95% Cl: 58-84%), which was significantly higher than the sensitivity of 47% obtained under an expert algorithm. The need for exploring this and other ways in which the VA technique can be improved are discussed. The implications of less-than-perfect sensitivity and specificity are explored using numerical examples. Misclassification bias should be taken into consideration when planning and evaluating epidemiological studies.

Algorithms↗

PubMed1991

Risk assessment for HIV infection: validation study of a computer-assisted preliminary screen.

Development has been undertaken for microcomputer software intended to assess individual risk for HIV infection by analyzing personal case histories pertinent to drug abuse, receptive blood transfusion, and sexual behavior. The software performs interactive confidential interviews of individuals desiring expert assistance when deciding whether to commit to an antibody test. In the first phase of a validation study, 87 subjects responded to the computer interview. For each subject, human immunodeficiency virus (HIV) antibody status was on clinical record. This sample included 70 subjects, 29 of whom were HIV seropositive, recruited from the clientele of an AIDS antibody testing and counseling facility. In this phase, the software accurately assessed 28 of 29 seropositives (96.6%) to be at risk for HIV. The second phase was based upon participation of an additional 74 subjects who were undergraduates at the University of Oklahoma. In this presumed low-risk sample, 55 members reported never having previously tested for HIV antibodies. Seven members (12.7%) of the untested group were declared at risk in the course of receiving confidential computer screen advice. Of these 7, there were 3 members (42.9%) who were motivated by the computer to voluntarily seek HIV antibody testing. Of the 7 declared at risk, 2 members (3.9%) were among the 51 seronegative subjects classified as heterosexuals without specific and identified risks. All Phase II subjects seeking follow-up antibody tests were found seronegative.

Diagnosis, Computer-Assisted↗

PubMed1990

Validation study methods for estimating exposure proportions and odds ratios with misclassified data.

Two methods for making adjustments to an estimate of exposure when data are possibly misclassified are discussed. One, the indirect method, is widely used but the other, the direct method, seems less well-known, despite it being a rather more obvious approach. To implement either requires some knowledge of misclassification rates and it may be possible to estimate these by a validation study. Depending on how sampling for such a study is done, one has the choice of what method to use. Formulae for the variance of estimates are derived and the precision of the methods compared. The direct approach is found to be more efficient.

Environmental Exposure↗

PubMedDate not supplied

FETAX interlaboratory validation study: phase III--Part 1 testing.

The Frog Embryo Teratogenesis Assay-Xenopus (FETAX) is a 96-h whole embryo developmental toxicity screening assay that can be used in ecotoxicology and in detecting mammalian developmental toxicants when an in vitro metabolic activation system is employed. A standardized American Society for Testing and Materials (ASTM) guide for the conduct of FETAX has been published, along with a companion atlas that aids in embryo staging and identifying malformations. As part of the ASTM process, a three-phase interlaboratory validation study was undertaken to evaluate the repeatability and reliability of FETAX. Seven different participants collaborated in the study. In Phase I, FETAX proved to be more repeatable and reliable than many bioassays. However, some excessive variation was observed in a few laboratories. An initial lack of assay experience by some technicians caused variation. Phase II showed far less intra- and interlaboratory variability than Phase I. Non-teratogens showed the most consistent results, while more variability was observed for the two teratogens tested. Interlaboratory coefficient of variation values for all endpoints ranged from 7.3 to 54.7. Phase III--Part 1, using coded samples and test concentration ranges selected by each laboratory, showed results similar to Phase I. Analysis of the causes of variation suggested that some technicians judged some embryos to be malformed while others consistently judged similar embryos as normal. Concentration ranges tested by some of the laboratories varied greatly and a new protocol for selecting concentrations for initial testing was written to reduce variation from this source. Testing to date suggests that FETAX is as repeatable and reliable as other standard bioassays.

Aminopropionitrile↗

PubMed1989

The anxiety thermometer: a validation study.

The aim of our study was to provide validation and reproducible data for the anxiety thermometer. This thermometer is either a continuous or a 10-point Likert-type scale on which subjects are asked to rate their anxiety feelings at a particular moment. It is a quick way to measure state-anxiety. As a validation criterion the State-Trait Anxiety Inventory (STAI) A-State scale was used. To test the reproducibility of the thermometer, a test-retest correlation coefficient was calculated, with a retrospective second thermometer score. The ego-threatening situation used was a written examination. Two experiments were carried out during different examination conditions. The data consistently indicated that the validity and reproducibility of the anxiety thermometer is fair (correlation coefficients between .60 and .78) In the second study, the possible influence of two factors on the retrospective scores were additionally tested.

Adult↗