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PubMed2004

Estimation of a parameter and its exact confidence interval following sequential sample size reestimation trials.

For confirmatory trials of regulatory decision making, it is important that adaptive designs under consideration provide inference with the correct nominal level, as well as unbiased estimates, and confidence intervals for the treatment comparisons in the actual trials. However, naive point estimate and its confidence interval are often biased in adaptive sequential designs. We develop a new procedure for estimation following a test from a sample size reestimation design. The method for obtaining an exact confidence interval and point estimate is based on a general distribution property of a pivot function of the Self-designing group sequential clinical trial by Shen and Fisher (1999, Biometrics55, 190-197). A modified estimate is proposed to explicitly account for futility stopping boundary with reduced bias when block sizes are small. The proposed estimates are shown to be consistent. The computation of the estimates is straightforward. We also provide a modified weight function to improve the power of the test. Extensive simulation studies show that the exact confidence intervals have accurate nominal probability of coverage, and the proposed point estimates are nearly unbiased with practical sample sizes.

Biometry↗
PubMedDate not supplied

How can we do pharmacokinetic studies in the tropics?

Information regarding the pharmacokinetic (PK) and pharmacodynamic (PD) properties of a drug provides the basis for optimizing dosing. PK-PD information should be obtained from patients representative of the overall target population, but in many tropical hospitals or health care facilities it may be medically hazardous or logistically difficult for an ill patient or a young child to be sampled repeatedly. Traditional methods used to determine the pharmacokinetic properties of a drug require analysis of a large number of blood samples per subject. However, using modern statistical methods, sparse datasets (i.e. with assay results from only a few, or as little as one blood sample per subject) can now be analysed by a method termed 'the population approach'. Modern assay techniques can often be adapted to small blood volumes allowing finger prick blood samples to be taken. One of the major aims of the population approach is to distinguish and characterize patient and disease contributors to inter-individual variance in drug pharmacokinetics. The purpose of this paper is to explain the basis of the population approach, to highlight its advantages compared to traditional methods of analysis, and to review the application of the population approach to data from field studies of antimalarial drugs. The design of population pharmacokinetic studies is also discussed briefly. The principles discussed in the paper are also applicable to pharmacodynamic data.

Antimalarials↗
PubMed2002

[Blood alcohol content prevalence among trauma patients seen at a level 1 trauma center].

OBJECTIVE: To investigate the prevalence of blood alcohol content (BAC) among patients seen at a level 1 trauma center. METHODS: A cross-sectional study was carried out and patients were randomly selected at the emergency room of a level I trauma center in the city of São Paulo, Brazil, throughout a year (August 1998 to August 1999). Blood samples were drawn and data was collected using an adapted version of a questionnaire developed by the Medical Research Institute of San Francisco - Alcohol Research Group. RESULTS: A population sample of 464 patients was analyzed. Most of them were males (73.7%) and the median age was 29 years old. Positive BAC was found in 28.9% of the cases (CI95% 24.8 - 33.2) and in 84.3% BAC was =0.10%. Type of injury, gender, age group, marital status and outcome showed statistically significant associations with BAC with the highest BAC prevalence observed among assault victims (46.2%), males (33.9%), 25 to 44 years old (37.6%), singles (33.0%), and patients admitted in the hospital (41.4%). CONCLUSIONS: The results reinforce the relationship of alcohol and trauma. Preventive actions at different levels focusing on higher risk groups for alcohol-related injuries should be considered as part of prevention programs to both reduce injuries and curb recurrent events.

Adolescent↗
PubMed1991

Assessing differences in chemically dependent adolescent males using the Child Behavior Checklist.

A study was conducted with 59 chemically dependent (CD) male adolescents (ages 13 to 16) using the Child Behavior Checklist (CBC). The CD sample was compared to a normative group on four adaptive behavior scales and twelve behavior problem scales, and was found to be significantly different on all measures. The CD sample was also compared to a general clinical group on nine behavior problem scales, and was found to score significantly higher on scales measuring delinquent and uncommunicative behaviors, and significantly lower on scales measuring immature and hostile-withdrawn behaviors. Summary profile types were compared with the clinical population and a separate assaultive/aggressive population. More of the CD population fit an uncommunicative/delinquent profile type and relatively fewer fit schizoid and immature/aggressive profile types as compared to the two other groups. The CBC differentiated subgroups in the CD sample with respect to completion of treatment and type of drug used, but not motivation for treatment at admission.

Adolescent↗
PubMed1984

Two-dimensional echocardiographic guiding of endomyocardial biopsy.

Two-dimensional echocardiography provides adequate spatial orientation and anatomic definition. Eighteen consecutive patients undergoing myocardial biopsy had concomitant two-dimensional echocardiography during 22 biopsies of five to six samples each. The transducer was placed at the apex and in the subcostal area and four-chamber views were used. The bioptome was seen entering the right atrium and crossing the tricuspid valve to the right ventricle. The catheter was then manipulated under two-dimensional echocardiography and the tip's position was strictly adapted, using two different classic views before sampling. The success rate in visualizing the forceps and in defining the site of sampling was 100 percent, and no complication was noted. Radiation exposure was largely reduced. Two-dimensional echocardiography to guide endomyocardial biopsy may reduce the risk of perforation by a better anatomic definition of the sampling site. It permits sampling from different ventricular sites or from the same site during serial procedures for monitoring evolution or treatment.

Adult↗
PubMed2003

The Turkish version of the Auditory Consonant Trigram Test as a measure of working memory: a normative study.

The following study was conducted to adapt the Auditory Consonant Trigram Test (ACT) to Turkish, acquire a new and larger set of normative data, and finally investigate the reliability and validity of the adapted version. The data were collected from a sample of 236 healthy individuals. To test the validity of the Turkish version of ACT, the normative results of ACT were first compared with those obtained from the Digit Span Test (DST) backwards section. Secondly, the ACT performance of 53 schizophrenic patients was compared with that of a matched group selected from the normative sample. Age and education variables influenced performance, whereas gender did not in the normal sample. The ACT and DST backwards scores were positively correlated. As expected, the ACT performance was worse in schizophrenic patients compared to controls. The internal consistency of the adapted version of ACT was found to be at a reliable level (alpha=0.8535). The Turkish version of ACT can be considered to be a reliable and valid measure of working memory.

Adolescent↗
PubMed2003

How well do fourth year Wits dental students place resin composite restorations?

OBJECTIVES: To evaluate, by means of a scanning electron microscope (SEM) the quality of resin composite restorations, placed as a first attempt by fourth-year dental students. METHODS: Ten Class IV direct composite restorations, placed in plaster-mounted extracted incisor teeth as part of pre-clinical course requirements, were selected. Specimens were evaluated and graded on a two-point scale by a staff member according to departmental clinical evaluation criteria. Five restored teeth were prepared for surface evaluation of marginal integrity, surface roughness and contour using SEM. The remaining specimens were embedded in resin and ground down transversely, parallel to the incisal edge until a dentine core was apparent. The ground surfaces were polished, prepared for SEM and assessed for etched layer, placement of bonding agent, composite adaptation and overall consistency. RESULTS: Clinical assessment and SEM surface evaluation correlated favourably for all criteria, except contour, indicating that students were reasonably competent in finishing techniques. Ground samples revealed acceptable etched enamel layers and marginal adaptation. Bonding agent thickness varied between 0 and 200 microns casting doubt on procedural accuracy. Porosities and voids were apparent within the resin composite. Internal features were the main reason for unsatisfactory grades. CONCLUSIONS: Students placed restoration satisfactorily. They would benefit if able to examine sectioned restorations to understand critical placement techniques which would contribute to resin composite restoration success. A research component can be introduced into the dental undergraduate curriculum by way of similar projects linked to didactic course-work.

Clinical Competence↗
PubMed2004

Sample designs and sampling methods for the Collaborative Psychiatric Epidemiology Studies (CPES).

This paper provides an overview of the probability sample designs and sampling methods for the Collaborative Psychiatric Epidemiology Studies (CPES): the National Comorbidity Survey Replication (NCS-R), the National Study of American Life (NSAL) and the National Latino and Asian American Study of Mental Health (NLAAS). The multi-stage sample design and respondent selection procedures used in these three studies are based on the University of Michigan Survey Research Center's National Sample designs and operations. The paper begins with a general overview of these designs and procedures and then turns to a more detailed discussion of the adaptation of these general methods to the three specific study designs. The detailed discussions of the individual study samples focus on design characteristics and outcomes that are important to analysts of the CPES data sets and to researchers and statisticians who are planning future studies. The paper describes how the expected survey cost and error structure for each of these surveys influenced the original design of the samples and how actual field experience led to changes and adaptations to arrive at the final samples of each survey population.

Adult↗
PubMed1988

Influence of inorganic and organic nutrients on aerobic biodegradation and on the adaptation response of subsurface microbial communities.

The influence of inorganic and organic amendments on the mineralization of ethylene dibromide, p-nitrophenol, phenol, and toluene was examined in subsurface soil samples from a pristine aquifer near Lula, Okla. The responses indicate that the metabolic abilities and nutrient requirements of groundwater microorganisms vary substantially within an aquifer. In some samples, additions of inorganic nutrients resulted in a more rapid adaptation to the test substrate and a higher rate of metabolism, indicating that metabolism may have been limited by these nutrients. In other samples from the same aquifer layer, inorganic amendments had little or no influence on mineralization. In general, the addition of multiple inorganic nutrients resulted in a greater enhancement of degradation than did the addition of single substances. Additions of alternate carbon sources, such as glucose or amino acids, inhibited the mineralization of the xenobiotic substrates. This inhibition appears to be the result of the preferential utilization of the more easily degradable carbon amendments.

Adaptation, Biological↗
PubMed1993

2H NMR lineshapes of immobilized uniaxially oriented membrane proteins.

As a method for the structure determination of integral membrane proteins or other large macromolecular complexes, a solid state 2H NMR approach is presented, capable of measuring the orientations of individual chemical bond vectors. In an immobilized uniaxially oriented sample, the bond angle of a deuterium-labelled methyl group relative to the axis of ordering can be calculated from the quadrupole splitting in the "zero-tilt" spectrum where the sample normal is aligned parallel to the spectrometer field direction. However, since positive and negative values of this splitting cannot be distinguished, there may appear to be two solutions, of which only one describes the correct molecular geometry. We show that it is possible to determine the bond angle uniquely between 0 degree and 90 degrees, by analysing the lineshapes of a tilt series of spectra acquired over different sample inclinations. The lineshape equation describing such oriented 2H NMR spectra will be derived (for asymmetry parameter eta = 0) and discussed, with an illustration of the various linebroadening effects from which the orientational distribution function in the macroscopically ordered system can be determined. This strategy is then applied to specifically deuterium-labelled retinal in dark-adapted bacteriorhodopsin, prepared in a uniaxially oriented sample from purple membrane fragments. From the quadrupole splitting in the zero-tilt spectrum and by lineshape simulations, the deuteromethyl group at C20 on retinal is found to make an angle of 32 degrees +/- 1 degree with the membrane normal, and the sample mosaic spread to be around +/- 8 degrees. The resulting orientation of retinal is in excellent agreement with its known structure in bacteriorhodopsin, and together with the results on other methyl groups it will be possible to construct a detailed picture of the chromophore in the protein binding pocket.

Bacteriorhodopsins↗
PubMed1995

Adaptation to homelessness: self-actualization, loneliness, and depression in street homeless men.

Adaptation to homelessness was investigated in a sample of 145 street homeless men using loneliness and depression scales and the construct of self-actualization. Principal components analysis with varimax rotation of a matrix of correlations of measures on the history of being homeless, demographic data, scores on loneliness and depression scales, and self-actualization measures gave a 3-factor model of adjustment: adaptive striving, detachment, and adaptive resources. Maslow's and Sullivan's contention that satisfying interpersonal relationships are common pathways to mental health was affirmed.

Adaptation, Psychological↗
PubMed1995

Bivariate cytokeratin/DNA flow cytometric analysis of paraffin-embedded samples from colorectal carcinomas.

Admixture of normal and neoplastic cells is a serious problem in the evaluation of tumor cell kinetic parameters by flow cytometry, in particular for DNA diploid tumors. The admixture of non-neoplastic cells, such as stromal cells and inflammatory cells, can disturb the estimation of the proliferative tumor fraction. This problem has been addressed in fresh tumor samples by applying bivariate flow cytometric analyses for DNA and cytokeratin. We have adapted this approach for formalin-fixed and paraffin-embedded tissue samples of colorectal carcinomas. After preparation of a single cell suspension from paraffin blocks by means of an enzymatic digestion step, the cells of epithelial origin were selectively stained with a panel of subtype specific cytokeratin antibodies. DNA analysis could thus be performed on the cytokeratin-positive cells. The proliferative fractions of the paraffin-embedded samples could be compared with those of the fresh tissue samples and a very good correlation was seen between DNA indices from fresh and paraffin-embedded material. As expected, after gating on the cytokeratin-positive cells an enrichment of the S-phase fraction was seen compared with the ungated cell population. However, this enrichment was more pronounced in the cell suspensions derived from the paraffin-embedded part of the tumor compared with the fresh disaggregated, ethanol-fixed part of the tumor.

Aneuploidy↗
PubMedDate not supplied

Factors affecting older adults' use of adaptive equipment: review of the literature.

OBJECTIVE: The purpose of this review was to identify the major findings of published research on the factors influencing older adults' use of adaptive equipment. METHOD: Fourteen studies involving an older adult sample were selected from major electronic bibliographic databases searched with a series of key words related to aging and equipment use. Results of these studies were compared to determine the most common factors influencing the use of adaptive equipment among older adults. RESULTS: Although the reviewed studies varied in their sampling strategies and designs, many results were similar. Between 47% and 82% of prescribed equipment continues to be used by older adults, with use decreasing over time. Findings from published studies show that equipment suitability, adequate training, and pre-prescription home visits contribute to these rates of use. Lack of fit among the person, his or her environment, and the equipment was the primary reason identified for nonuse. CONCLUSION: The results of the published research provide practicing occupational therapists with a range of factors to consider when prescribing adaptive equipment to older adults. Although the findings of this review demonstrate remarkable consistency across existing research findings, future research is needed to identify what constitutes optimal device use, what factors provide personal motivation for using assistive devices, and how home visits influence use.

Persons with Disabilities↗
PubMed2006

An improved analytical method for the determination of urea nitrogen isotopomers in biological samples utilizing continuous flow isotope ratio mass spectrometry.

Over the past few years numerous dual inlet isotope ratio mass spectrometry (IRMS) applications have been adapted to continuous flow systems which allow the automation of sample admission and a higher throughput. The isotopomer analysis of urea nitrogen by IRMS requires the offline conversion of urea into nitrogen gas before analysis. The oxidation of urea with LiOBr results in the monomolecular degradation of urea, which preserves the identity of the parent urea molecule, and has to be conducted under vacuum to prevent contamination with atmospheric nitrogen. We have developed an offline system of urea degradation utilizing disposable Exetainers, in which atmospheric nitrogen is displaced by helium. Recovery of urea nitrogen was linear within the range of the standards tested (0 to 420 microg nitrogen) and standard curves for 15N15N-urea standards showed high coefficients of determination (R2 > 0.9998). A small portion of urea degrades in a non-monomolecular fashion and has been shown to depend on the concentration of urea in the sample. Long-term storage of prepared samples showed a decline in 15N15N enrichment, suggesting air contamination. However, samples were stable for 24 h, which allows for the analysis of large sample batches. Interest in urea metabolism, particularly in ruminant species, has increased recently due to the environmental implications of urea and nitrogen excretion by farm animals. This novel analytical method will allow for accurate measurements and the rapid throughput needed in order to support these field studies.

Animals↗
PubMed2003

Flash-induced relaxation changes of the EPR signals from the manganese cluster and YD reveal a light-adaptation process of photosystem II.

By exposing photosystem II (PSII) samples to an incrementing number of excitation flashes at room temperature, followed by freezing, we could compare the Mn-derived multiline EPR signal from the S2 oxidation state as prepared by 1, 5, 10, and 25 flashes of light. While the S2 multiline signals exhibited by these samples differed very little in spectral shape, a significant increase of the relaxation rate of the signal was detected in the multiflash samples as compared to the S2-state produced by a single oxidation. A similar relaxation rate increase was observed for the EPR signal from Y(D*). The temperature dependence of the multiline spin-lattice relaxation rate is similar after 1 and 5 flashes. These data are discussed together with previously reported phenomena in terms of a light-adaptation process of PSII, which commences on the third flash after dark-adaptation and is completed after 10 flashes. At room temperature, the fast-relaxing, light-adapted state falls back to the slow-relaxing, dark-adapted state with t(1/2) = 80 s. We speculate that light-adaptation involves changes necessary for efficient continuous water splitting. This would parallel activation processes found in many other large redox enzymes, such as Cytochrome c oxidase and Ni-Fe hydrogenase. Several mechanisms of light-adaptation are discussed, and we find that the data may be accounted for by a change of the PSII protein matrix or by the light-induced appearance of a paramagnetic center on the PSII donor side. At this time, no EPR signal has been detected that correlates with the increase of the relaxation rates, and the nature of such a new paramagnet remains unclear. However, the relaxation enhancement data could be used, in conjunction with the known Mn-Y(D) distance, to estimate the position of such an unknown relaxer. If positioned between Y(D) and the Mn cluster, it would be located 7-8 A from the spin center of the S2 multiline signal.

Adaptation, Physiological↗
PubMed2001

Selective adaptation to noxious foods by a herbivorous insect.

When animals repeatedly sample a noxious food over a period of 1-4 days, they can markedly reduce their aversive behavioral response to the diet's unpleasant taste (e.g. 'bitterness') or toxic effects. This long-term adaptation process is selective, however, permitting insects to adapt physiologically to some but not all noxious foods. We hypothesized (i) that the selective nature of this adaptation process stems from the fact that some unpalatable foods are toxic while others are harmless and (ii) that insects have more difficulty adapting to foods that are both unpalatable and toxic. Our model system consisted of Manduca sexta caterpillars and two compounds that taste bitter to humans and elicit an aversive behavioral response in this insect (salicin and aristolochic acid). We found that 2 days of exposure to a salicin diet completely adapted the aversive response of the caterpillars to salicin, but that exposure to an aristolochic acid diet failed to adapt the aversive response to aristolochic acid. We determined that M. sexta could not adapt to the aristolochic acid diet because it lacked mechanisms for reducing the compound's toxicity. In contrast, the salicin diet did not produce any apparent toxic effects, and the caterpillars adapted to its aversive taste within 12 h of exposure. We also found that the salicin adaptation phenomenon (i) was mediated by the central gustatory system, (ii) generalized to salicin concentrations that were twice those in the adapting diet and (iii) offset spontaneously when the caterpillar was transferred to a salicin-free diet. We propose that toxicity is a more significant barrier to dietary adaptation than 'bitterness' in this insect.

Adaptation, Physiological↗
PubMed2000

Comparison of the particle size distribution of heavy-duty diesel exhaust using a dilution tailpipe sampler and an in-plume sampler during on-road operation.

Originally constructed to develop gaseous emission factors for heavy-duty diesel trucks, the U.S. Environmental Protection Agency's (EPA) On-Road Diesel Emissions Characterization Facility has been modified to incorporate particle measurement instrumentation. An electrical low-pressure impactor designed to continuously measure and record size distribution data was used to monitor the particle size distribution of heavy-duty diesel truck exhaust. For this study, which involved a high-mileage (900,000 mi) truck running at full load, samples were collected by two different methods. One sample was obtained directly from the exhaust stack using an adaptation of the University of Minnesota's air-ejector-based mini-dilution sampler. The second sample was pulled from the plume just above the enclosed trailer, at a point approximately 11 m from the exhaust discharge. Typical dilution ratios of about 300:1 were obtained for both the dilution and plume sampling systems. Hundreds of particle size distributions were obtained at each sampling location. These were compared both selectively and cumulatively to evaluate the performance of the dilution system in simulating real-world exhaust plumes. The data show that, in its current residence-time configuration, the dilution system imposes a statistically significant bias toward smaller particles, with substantially more nanoparticles being collected than from the plume sample.

Air Pollution↗
PubMed1988

Sample sizes based on the log-rank statistic in complex clinical trials.

The log-rank test is frequently used to compare survival curves. While sample size estimation for comparison of binomial proportions has been adapted to typical clinical trial conditions such as noncompliance, lag time, and staggered entry, the estimation of sample size when the log-rank statistic is to be used has not been generalized to these types of clinical trial conditions. This paper presents a method of estimating sample sizes for the comparison of survival curves by the log-rank statistic in the presence of unrestricted rates of noncompliance, lag time, and so forth. The method applies to stratified trials in which the above conditions may vary across the different strata, and does not assume proportional hazards. Power and duration, as well as sample sizes, can be estimated. The method also produces estimates for binomial proportions and the Tarone-Ware class of statistics.

Clinical Trials as Topic↗