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PubMed2000

A note on the statistical power in extended twin designs.

The power to detect sources of genetic and environmental variance varies with sample size, study design, effect size and the statistical significance level chosen. We explored whether the power of the classical twin study may be increased by adding non-twin siblings to the classical twin design. Sample sizes to detect genetic and shared environmental variation were compared for kinships with only twins, kinships consisting of twins and one additional sibling, and kinships with twins and two additional siblings. The effect of adding siblings to the classical twin design was considered for univariate and bivariate analyses. For the univariate case, adding one non-twin sibling resulted in a decrease in sample size needed to detect additive genetic influences in the presence of environmental influences. However, adding two additional siblings did not decrease the number of subjects as compared to the classical twin design. The sample size required to detect common environmental factors was also greatly decreased by adding one non-twin sibling. Adding two non-twin siblings resulted in a small additional decrease. In models including additive genetic, dominant genetic, and unique environmental effects, adding one sibling to a twin family decreased the required sample size to detect dominant genetic influences. Adding two siblings to a twin family resulted in only a slight additional decrease in sample size. In the bivariate case a similar pattern of results was found, in addition to the observation that the overall required sample size, as expected, was lower than in the univariate case. The decrease in sample size from bivariate testing was more pronounced in a design with one or two additional siblings, as compared to a design with twins only. It is concluded that a well considered choice of family design, i.e. including families with twins and one or two additional siblings increases the statistical power to detect sources of variance due to additive and non-additive genetic influences, and common environment.

Analysis of Variance↗
PubMed2002

Automated headspace solid-phase dynamic extraction for the determination of amphetamines and synthetic designer drugs in hair samples.

The technique of automated headspace solid-phase dynamic extraction (SPDE) coupled with gas chromatography-mass spectrometry was evaluated for the determination of amphetamines and synthetic designer drugs in hair samples. Headspace SPDE is a novel method for the solventless extraction of organic compounds in aqueous samples. In a so-called inside needle capillary absorption trap a hollow needle with an internal coating of polydimethylsiloxane is used as extraction and preconcentration medium. Sampling is performed on the solution headspace by passing the gas through the device actively by a syringe. Analytes present in the sample are sorbed onto the deposited stationary phase. The syringe needle is placed into the injection port of a GC and rapid heating of the metal needle induces the desorption of analytes. For the determination of amphetamine, methamphetamine, 3,4-methylendioxyamphetamine (MDA), 3,4-methylendioxymethamphetamine, 3,4-methylendioxyethylamphetamine (MDEA), 3,4-methylendioxyphenyl-2-butanamine and N-methyl-1-(3,4-methylendioxyphenyl)-2-butanamine in human hair samples, 10 mg of hair were hydrolysed with sodium hydroxide. After absorption of analytes for an on-coating derivatization procedure the SPDE needle was directly placed into the headspace of a second vial containing N-methyl-bis(trifluoroacetamide). A validation procedure revealed absolute analyte recoveries between 10.2 and 16.7%. Linearity was obtained from 0.1 to 20 ng/mg with coefficients of correlation between 0.992 and 0.999. Intra- and inter-day precision were determined at two different concentrations and resulted in ranges between 1.4 and 4.1% (intra-day) and 4.2-14.6% (inter-day). Limits of detection between 0.03 ng/mg (MDA) and 0.19 ng/mg (MDEA) were achieved. Results indicated that SPDE is a rapid and sensitive method for the analysis of biological samples. Compared to solid-phase microextraction we found a higher extraction rate coupled with a faster automated operation.

Amphetamines↗
PubMed1992

Application of capillary isoelectric focusing with universal concentration gradient detector to the analysis of protein samples.

The design of a new capillary isoelectric focusing (cIEF) instrument, composed of a rugged cartridge holding a short piece of capillary and a universal, inexpensive concentration gradient detector, was optimized and applied to the analysis of various protein samples. High-efficiency cIEF separations with sub-femtomole detection limits for absolute amounts were obtained using 10 microns I.D. capillaries with large O.D.-to-I.D. ratios. An electric field strength of 1 kV/cm applied in the focusing step resulted in a 10(-8) M on-column concentration detection limit, which corresponded to 10(2) amol absolute amount of proteins. The detection volume was estimated to be 2 pl, which is among the smallest values reported to date for any optical or spectroscopic detector. When a 6-cm long capillary was used, proteins with isoelectric points ranging from 4.7 to 8.8 could be analyzed in about 5 min, the shortest analysis time ever reported for cIEF. Compared with commercial cIEF instruments with UV-visible absorbance detectors, the instrument is easier to use and has lower detection limits and better resolution. Several protein mixtures and real samples were separated with this instrument.

Antibodies, Monoclonal↗
PubMed1988

An evaluation of optimal sampling strategy and adaptive study design.

We have evaluated the utility of optimal sampling strategy coupled with adaptive study design in the determination of individual patient and population pharmacokinetic parameter values. In 9 patients with cystic fibrosis receiving a short (1 minute) infusion of ceftazidime pharmacokinetic parameter values were determined with a nonlinear least-squares estimator analyzing a traditional, geometrically spaced set of 12 postinfusion serum samples drawn over 8 hours. These values were compared with values generated from four sample subsets of the 12 obtained at optimal times and analyzed by nonlinear least-squares estimator, as well as a maximum a posteriori probability Bayesian estimator with prior distributions placed on beta and clearance. The four sampling times were determined according to an adaptive design optimization technique that employs sequential updating of population prior distributions on parameter values. Compared with the 12-point determination, the four optimal points analyzed with the maximum a posteriori probability Bayesian estimator faithfully reproduced both microscopic and hybrid pharmacokinetic parameter values for individual patients and, consequently, also produced accurate measures of population central tendency and dispersion. This has important implications in being able to more efficiently derive target patient population pharmacokinetic information for new drugs. This should also allow generation of better concentration-effect relationships in populations of interest.

Adolescent↗
PubMed1996

Comparison of some practical sampling strategies for population pharmacokinetic studies.

Using population analysis, sparsely sampled Phase 3 clinical data can be utilized to determine the pharmacokinetic characteristics of the target population. Data arising from such studies are likely to be constrained to certain sampling windows, i.e., the visiting hours at the study clinic. When the sampling window is narrow compared to the half-life of the drug, the advantage of taking more than one sample is not obvious. Study designs with one or two samples per visit have been compared with respect to (i) precision and bias of the population parameter estimates, (ii) the ability to identify the underlying pharmacokinetic model, and (iii) the estimation of individual parameter values. The first point was assessed using simulated data while the latter two were studied using a real data set. Results show: (i) Parameter estimates are more biased and imprecise when only one sample is taken compared to when two samples are obtained, this is true irrespective of the time span between the two samples. (ii) Ability to identify a more complex model is increased if two samples are taken. Specifically, the variability between occasions can be quantified. (iii) Two-sample designs are generally better with respect to prediction of individual parameter values. Even minor changes to commonly employed study designs, in this case the addition of one sample at each study occasion, can improve quality and quantity of the information obtained.

Computer Simulation↗
PubMed2003

Capturing ion exchanger-bound infectious pancreatic necrosis virus--design and application for large volume water samples.

A method was designed for rapid and reliable demonstration of the presence of infectious pancreatic necrosis virus retrieved from 5 l water samples. Viruses together with an added carrier protein were adsorbed to a resin of an added anion exchanger. Then the resin was collected rapidly and quantitatively through a specific device which we designed. The resin was transferred to a column from which the viruses were eluted, and subsequently further concentrated by acid precipitation, followed by SDS-polyacrylamide gel electrophoresis and Western blot analysis. Serological results were obtained within 24 h after the water sample was introduced into the laboratory. Proteins were recovered at an efficiency between 70 and 80% and the total concentration factor ranged between 150000 and 250000 times, depending on the requirements and the methods of choice.

Adsorption↗
PubMed2005

Estimation of AUC from 0 to Infinity in Serial Sacrifice Designs.

Nonclinical in vivo animal studies have to be completed before starting clinical studies of the pharmacokinetic behavior of a drug in humans. The drug exposure in animal studies is often measured by the area under the concentration time curve (AUC). The classical complete data design where each animal is sampled for analysis once per time point is usually only applicable for large animals. In the case of rats and mice, where blood sampling is restricted, the batch design or the serial sacrifice design need to be considered. In batch designs samples are taken more than once from each animal, but not at all time points. In serial sacrifice designs only one sample is taken from each animal. This paper presents an estimator for AUC from 0 to infinity in serial sacrifice designs, the corresponding variance and its asymptotic distribution.

Algorithms↗
PubMed2006

Establishing bioequivalence in serial sacrifice designs.

Nonclinical in vivo animal studies have to be completed before starting clinical studies of the pharmacokinetic behavior of a drug in human subjects. The classic complete data design, where each animal is sampled for analysis once per time point, is usually only applicable for large animals using the traditional two-stage approach. The first stage involves estimation of pharmacokinetic parameters for each animal separately and the second stage uses the individual parameter estimates for statistical inference. In the case of rats and mice, where blood sampling is restricted, the batch design or the serial sacrifice design may be applicable. In batch designs samples are taken more than once from each animal, but not at all time points. In serial sacrifice designs only one sample is taken from each animal. In this paper, three methods are presented to construct confidence intervals for the ratio of two AUCs assessed in a serial sacrifice design, which can be used to assess bioequivalence in this parameter. The presented methods are compared in a simulation study.

Animals↗
PubMed1981

The design and use of a simple device for rapid quench-freezing of biological samples.

The detailed design of a simple device for rapid quench-freezing of biological samples under reproducible conditions is presented. With spring-augmented descent, sample immersion velocity of 10 m s-1 into a cryogenic liquid is achieved. Biological samples, loaded in Balzers planchets, Denton holders, or a newly designed 'titanium envelope', are suitable for rapid-freezing with this device. Using 4 micrometers titanium foil, light weight (1 mg) streamlined holders can easily be made to enclose cell suspensions or tissue samples. The foil envelope is designed for efficient heat dissipation while protecting the sample from possible impact or flow distortions occurring from spring-augmented immersion. Human erythrocytes, quench-frozen in the titanium envelope, were prepared for electron microscopy by the freeze-substitution technique. Two opposing 25--30 micrometers surface zones were frozen in the apparent absence of ice. The extended depth of cryofixation is attributed to the advantages of thin foil in the titanium envelope design and the use of rapid-immersion technique.

Erythrocytes↗
PubMed2006

Serum lipids and low back pain: an association? A follow-up study of a working population sample.

STUDY DESIGN: Cohort study with 5-, 10-, and 28-year follow-up. OBJECTIVES: To examine associations between baseline serum lipid concentrations and later low back pain (LBP). SUMMARY OF BACKGROUND DATA: Atherosclerosis of the lumbar vessels has been suggested as a mechanism leading to disc degeneration and LBP. Cholesterol is considered essential for atherosclerosis development. METHODS: A sample (n = 902) of employees in an engineering company was examined for serum total cholesterol and triglycerides, body mass index (BMI), smoking, exercise, work history, and LBP in 1973. By November 2000, 232 subjects had died. In 1978, 748 (84% of the survivors), in 1983, 654 (76%), and in 2000, 546 (81%) responded to a follow-up questionnaire. RESULTS: In men, baseline serum total cholesterol predicted new cases of radiating LBP in the 5-year follow-up (highest tertile vs. lowest: odds ratio [OR], 2.5; 95% confidence interval [CI], 1.1-5.9) and in the 10-year follow-up (OR, 2.8; 95% CI, 1.3-6.1), adjusted for age, occupational class, work history, BMI, smoking and exercise. Also, serum triglycerides predicted new cases in the latter examination (OR, 2.6; 95% CI, 1.2-5.8). In women, no associations were seen until the 10-year follow-up, when their results were similar to those in men. In the total material, serum total cholesterol predicted radiating LBP reported both at the 10- and the 28-year follow-up. CONCLUSIONS: High serum lipids predicted incident radiating LBP, consistent with the atherosclerosis-LBP hypothesis.

Adult↗
PubMed2005

Cultural competence among Ontario and Michigan healthcare providers.

PURPOSE: To examine variables associated with cultural competence among urban, hospital-based healthcare providers in Ontario (Canada) and Michigan (US). DESIGN AND SAMPLE: A cross-sectional descriptive design with a convenience sample of hospital-based providers was used. The sample was 145 providers (n=71 Ontario; n=74 Michigan). METHODS: Providers completed a survey which included the Cultural Competence Assessment (CCA) instrument. Regression analysis was used to examine associations. FINDINGS: Providers with diversity training and higher levels of educational attainment scored significantly higher on cultural awareness and sensitivity and on cultural competence behaviors. CONCLUSIONS: Variables significantly associated with cultural competence included prior training in cultural competency and higher educational attainment among both Ontario and Michigan healthcare providers.

Adult↗
PubMed1999

Application of the fractionator and vertical slices to estimate total capillary length in skeletal muscle.

A new stereological method is proposed which combines vertical slice projections with the fractionator to estimate the total capillary length in a skeletal muscle. The method was demonstrated on the soleus muscle of a Wistar rat. The implementation required capillary highlighting, tissue sampling, and data acquisition in the form of intersection counts between capillary projections and cycloid test lines. The capillaries were demonstrated using vascular perfusion (with gelatine) of the hind leg of the rat. The sampling procedure followed the fractionator design, namely a multistage systematic sampling design with a known sampling fraction at each stage. To make the design unbiased, vertical slices were used; for efficiency, the vertical axis was chosen parallel to the main axis of the muscle. As prescribed to avoid bias, the cycloid test lines were superimposed on the slice projections, viewed under the light microscope, with their minor axes normal to the vertical axis. The estimation precision was compared for different sampling and subsampling fractions. The proposed method was globally highly efficient, unbiased, and easy to implement.

Animals↗
PubMed2003

Sample size needed to detect gene-gene interactions using association designs.

It is likely that many complex diseases result from interactions among several genes, as well as environmental factors. The presence of such interactions poses challenges to investigators in identifying susceptibility genes, understanding biologic pathways, and predicting and controlling disease risks. Recently, Gauderman (Am J Epidemiol 2002;155:478-84) reported results from the first systematic analysis of the statistical power needed to detect gene-gene interactions in association studies. However, Gauderman used different statistical models to model disease risks for different study designs, and he assumed a very low disease prevalence to make different models more comparable. In this article, assuming a logistic model for disease risk for different study designs, the authors investigate the power of population-based and family-based association designs to detect gene-gene interactions for common diseases. The results indicate that population-based designs are more powerful than family-based designs for detecting gene-gene interactions when disease prevalence in the study population is moderate.

Genetic Predisposition to Disease↗
PubMed2006

Condition-related coping strategies in persons with spinal cord lesion: a cross-national validation of the Spinal Cord Lesion-related Coping Strategies Questionnaire in four community samples.

STUDY DESIGN: Cross-sectional, questionnaire. OBJECTIVES: Coping strategies employed to manage the consequences of a spinal cord lesion (SCL) have been found to be distinctly related to emotional well-being. However, research and clinical implications have been hampered by the lack of cross-validated measures that are directly related to the lesion and its consequences. This study investigates the psychometric performance of the SCL-related Coping Strategies Questionnaire in four different countries. SETTING: Austria, Germany, Switzerland and UK. METHODS: The study sample comprised 355 community residing persons with SCL. Multi-trait/multi-item analysis methods and non-parametric and parametric tests were used. RESULTS: The Acceptance coping scale showed satisfactory psychometric qualities, whereas there were some problems in the Fighting spirit scale and greater problems in the Social reliance scale. Compared with the Swedish developmental sample, Acceptance was used more in the four study countries. Consistent with the original sample, Acceptance and Fighting spirit coping correlated with fewer signs of emotional distress, persons lesioned > or = 5 years tended to report more Acceptance than the newly lesioned and coping strategies were mainly unrelated to neurological status. CONCLUSION: The English and German language versions of the Acceptance coping scale were valid and reliable, whereas some translated items in the Fighting spirit scale need to be revised. Translations of the Social reliance scale need to be thoroughly revised and retested. The results add further evidence to the literature on the stability of the link between adapting life priorities (ie Acceptance) and emotional well-being.

Adaptation, Psychological↗
PubMed2004

STR loci Penta D and Penta E: data from a Northern Thai population sample.

We designed new primers that give shorter amplicons for Penta D and Penta E for easy separation on native polyacrylamide gels. 112 unrelated Northern Thai men were typed. A total of nine and eight-teen alleles was found for Penta D and Penta E, respectively. Both loci showed a high power of discrimination (Penta D: 0.927; Penta E: 0.966; both loci combined: 0.9975) as reported in other populations. Penta D met Hardy-Weinberg expectations, whereas Penta E did not, maybe because of the small sample size in relation to the large number of alleles of this locus.

Alleles↗
PubMed1999

National probability samples in studies of low-prevalence diseases. Part II: Designing and implementing the HIV cost and services utilization study sample.

OBJECTIVE: The design and implementation of a nationally representative probability sample of persons with a low-prevalence disease, HIV/AIDS. DATA SOURCES/STUDY SETTING: One of the most significant roadblocks to the generalizability of primary data collected about persons with a low-prevalence disease is the lack of a complete methodology for efficiently generating and enrolling probability samples. The methodology developed by the HCSUS consortium uses a flexible, provider-based approach to multistage sampling that minimizes the quantity of data necessary for implementation. STUDY DESIGN: To produce a valid national probability sample, we combined a provider-based multistage design with the M.D.-colleague recruitment model often used in non-probability site-specific studies. DATA COLLECTION: Across the contiguous United States, reported AIDS cases for metropolitan areas and rural counties. In selected areas, caseloads for known providers for HIV patients and a random sample of other providers. For selected providers, anonymous patient visit records. PRINCIPAL FINDINGS: It was possible to obtain all data necessary to implement a multistage design for sampling individual HIV-infected persons under medical care with known probabilities. Taking account of both patient and provider nonresponse, we succeeded in obtaining in-person or proxy interviews from subjects representing over 70 percent of the eligible target population. CONCLUSIONS: It is possible to design and implement a national probability sample of persons with a low-prevalence disease, even if it is stigmatized.

Data Collection↗
PubMed1993

Dust from cotton manufacture: changing from static to personal sampling.

Several designs of personal samplers were tested for use to collect cotton dust. The IOM personal inhalable-dust sampler was selected because: (1) collection of the whole inhalable fraction was preferred, since all inhaled sizes are under suspicion as contributing to respiratory symptoms in cotton exposure; (2) this sampler is well characterized; and (3) it was found to be practicable in the environments examined. Gauze shields to exclude 'fly' from the personal sampler were tried, but were rejected mainly because measurement of the whole inhalable fraction by a validated sampler was felt to be more appropriate. A range of processes at a representative selection of mills was assessed by a hygiene team, and classified as 'clean' or 'dirty' in terms of present standards of control. This classification agreed well with subsequent measurements using the present method, which uses a large static sampler. A personal sampling survey then showed that in about two-thirds of 'clean' processes personal exposure of at least 80% of those employed was less than about 2-2.5 mg m-3. Only one-tenth of 'dirty' processes met this standard. Personal exposure correlates poorly with the present static method, as expected, but comparison of the results suggested that a mean background level of 0.5 mg m-3 would correspond to a median personal exposure of about 2.2 mg m-3. Side-by-side measurements by the background method differed by less than 0.15 mg m-3 on about 95% of occasions. Niven et al. (to be published) have compared the IOM head used in this study with the Manchester University sampler previously used by Cinkotai et al. [Ann. occup. Hyg. 32, 103-113 (1988)] to derive a relationship between personal exposure and prevalence of byssinotic symptoms in spinners. According to Cinkotai et al.'s results the concentrations of 2-2.5 mg m-3 discussed would correspond to a prevalence of 3-5%. However, this prevalence probably reflects higher exposures in the past.

Dust↗