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PubMed1992

Reactions of doctors to various forms of feedback designed to improve the sampling quality of cervical smears.

Three different forms of feedback designed to improve the sampling quality of cervical smears were tested in a randomized controlled trial among 179 physicians. The reactions of the doctors to the various interventions are reported as they appeared from their answers in a questionnaire. The influence of the interventions on the employed sampling technique is described on the basis of their answers to a telephone inquiry. The inclusion in laboratory protocols of an evaluation of the sampling quality of the submitted smears was largely appreciated, as was specific advice offered on indication. Monthly overviews comparing the performance of the individual doctor to that of his peers were esteemed by three out of four. Further information, help or training was requested more frequently than average by physicians obtaining inadequately sampled smears relatively often. The number of doctors using the combined spatula and Cytobrush method as sampling technique doubled during the study period.

Feedback↗
PubMed2003

Population pharmacokinetics of enfuvirtide in pediatric patients with human immunodeficiency virus: searching for exposure-response relationships.

OBJECTIVE: Our objective was to describe the population pharmacokinetics and pharmacodynamics of enfuvirtide acting on viral ribonucleic acid in children with human immunodeficiency virus 1. METHODS: A 1-compartment population pharmacokinetic model with first-order absorption and elimination was fit to subcutaneous and intravenous dose pharmacokinetic data from a 2-part study, as follows: an intensive-sample pharmacokinetic design (observed dose) (subcutaneous and intravenous, n = 12) followed by a sparse-sample design (unobserved dose) (subcutaneous, n = 15). The parameters of this model are clearance (CL), volume of distribution (V), absorption rate (k(a)), bioavailability (F), and both interindividual and residual variability. Plasma ribonucleic acid concentrations over time were used to build a population viral pharmacodynamics model with the following parameters: viral clearance (CL(v)), initial viral concentration (A(0)), duration (tau) and rate (R) of preinfected cell-based viral input after enfuvirtide was begun, and interindividual and residual variability. RESULTS: The mean population CL and V of enfuvirtide for a child with a mean body weight of 21.3 kg were 1.42 L/h and 5.67 L, respectively. Patient weight affected CL and V. Volume appeared to differ between intensive and sparse sampling occasions, and this difference also affected the residual error variance. Time after the beginning of therapy did not significantly affect any pharmacokinetic parameter, supporting the absence of metabolic induction and inhibition. Although trends were present, no statistically significant relationship was seen between any pharmacokinetic-based individual enfuvirtide exposure measure and any virologic response measure. CONCLUSIONS: Regarding pharmacokinetics and pharmacodynamics, no statistically significant correlation between exposure measures and viral clearance was observed.

Antiretroviral Therapy, Highly Active↗
PubMed2004

Design and simulation of sample pinching utilizing microelectrodes in capillary electrophoresis microchips.

The paper proposed novel designs to pinch the transverse diffusion of the sample in the injection mode using microelectrodes to generate the potential difference at the channel intersection in the capillary electrophoresis (CE) microchip. A pair of microelectrodes was used to conduct the injection channel and the separation channel, which directly provided the potential to pinch the sample without using a power supply. These new designs of the CE microchip simplify the electric circuitry and improve performance. Simulations were performed using the CFD-ACE[trade mark sign] software. The mechanisms of diffusion and electrophoresis were employed in the numerical simulation. The injection and separation processes of the sample were simulated and the parameters of the present design were investigated numerically.

Computer Simulation↗
PubMed2000

Study design in qualitative research--2: Sampling and data collection strategies.

In two prior papers in our series on qualitative research [Frankel & Devers (2000a, 2000b) Qualitative research: a consumer's guide, Education for Health, 13, 113-123; Frankel & Devers (2000) Study design in qualitative research-1: developing research questions and assessing research needs, Education for Health, 13, 251-261], we examine two critical issues in qualitative research design: sampling, including identifying and negotiating access to research sites and subjects, and data collection and management. We describe these two key steps in the qualitative research design process, discuss challenges that often emerge when pursuing these steps, and provide guidelines for addressing them. Qualitative research most often uses "purposive," rather than random, sampling strategies. A good understanding of these sampling strategies and why they are used is central to designing a credible qualitative study. In addition, given the real-world context in which most qualitative research is carried out, identifying and negotiating access to research sites and subjects are critical parts of the process. We also provide suggestions for developing and maintaining productive and mutually satisfying research relationships with sites and subjects. Finally, data collection and management are often neglected subjects in qualitative research. We offer practical advice on how to collect and manage qualitative data, including factors to consider when deciding how structured the data collection process should be, the pros and cons of audio- and/or videotaping compared with note-taking, and tips for writing up field notes and document management. A forthcoming, final paper in the series will focus on qualitative data analysis and the publication of qualitative research results.

Journal Article↗
PubMed2001

[Simplifying the sampling method for evaluating the larval density of Aedes aegypti in São Paulo State, Brazil].

OBJECTIVE: To suggest changes in the sampling procedures for estimating the larval density of Aedes aegypti in the state of São Paulo, Brazil, by assessing the efficacy and level of complexity of the current procedures. METHODS: The "Superintendência de Controle de Endemias do Estado de São Paulo" - SUCEN's (Superintendence for Endemic Control of the State of São Paulo) sampling procedures for estimating the density of Aedes aegypti larvae was assessed. The Breteau index with one-stage cluster sampling was applied. An average of 35 blocks, 14 buildings per block, of a total of 510 buildings per sample, were assessed. One hundred and eleven samples were obtained in 6 municipalities of São José do Rio Preto. RESULTS: The Breteau index estimates higher than 3 had coefficients of variation smaller than 30% in 71% of the samples. The design effect was 1.19 and 1.79 for indexes lower and higher than 5, respectively. The estimates were obtained in less than 3 days, requiring a daily average of 5.5 men per sampling. CONCLUSION: This sampling design revealed to be a simplified one: fast, economic and easily managed. The operational easiness was due to the use of the one-stage cluster sampling, when there was not need to prepare lists of addresses and then sort and locate the buildings. Though the design effect shows a slight loss of the estimates' accuracy with the use of one-stage cluster sampling, this was proven to be under acceptable range. Simplifying changes in the process of determining the sample size and assessing sampling errors are proposed.

Aedes↗
PubMed2001

Coupling pervaporation to AAS for inorganic and organic mercury determination. A new approach to speciation of Hg in environmental samples.

The design and development of a new approach for Hg speciation in environmental samples is described in detail. This method, consisting of the coupling of pervaporation and atomic absorption spectrometry, is based on a membrane phenomenon that combines the evaporation of volatile analytes and their diffusion through a polymeric membrane. It is proposed here as an alternative to gas chromatography for speciation of inorganic and organic Hg compounds, as the latter compounds are volatile and can be separated by applying the principles mentioned above. The interest of this method lies in its easy handling, low cost, and rapidity for the analysis of liquid and solid samples. This method has been applied to Hg speciation in a compost sample provided by a waste water treatment plant.

Calibration↗
PubMed2002

Precision of circular systematic sampling.

In design stereology, many estimators require isotropic orientation of a test probe relative to the object in order to attain unbiasedness. In such cases, systematic sampling of orientations becomes imperative on grounds of efficiency and practical applicability. For instance, the planar nucleator and the vertical rotator imply systematic sampling on the circle, whereas the Buffon-Steinhaus method to estimate curve length in the plane, or the vertical designs to estimate surface area and curve length, imply systematic sampling on the semicircle. This leads to the need for predicting the precision of systematic sampling on the circle and the semicircle from a single sample. There are two main prediction approaches, namely the classical one of G. Matheron for non-necessarily periodic measurement functions, and a recent approach based on a global symmetric model of the covariogram, more specific for periodic measurement functions. The latter approach seems at least as satisfactory as the former for small sample sizes, and it is developed here incorporating local errors. Detailed examples illustrating common stereological tools are included.

Analysis of Variance↗
PubMed2005

Optimisation of sampling for the temporal monitoring of technetium-99 in the Arctic marine environment.

Monitoring of the marine environment for radioactivity, for both radiological protection and oceanographic purposes, remains an expensive and labour intensive activity due to the large sample volumes needed and the complex and lengthy analytical procedures required to measure low levels of contamination. Because of this, some consideration must be given to the design of sampling plans to ensure effective and efficient sampling that can be defended on the basis of scientific rationale. This article tests the hypothesis that geostatistical techniques may prove of use in the optimisation and design of sampling regimes for the monitoring of temporal fluctuations in the levels of technetium at a location in the Norwegian Arctic marine environment. The level of temporal correlation exhibited by two relevant time series was investigated and the information used to observe the effect of sampling frequency on the production of monthly estimates of activity of technetium in both seawater and seaweed. The results indicate that reduced sampling frequency allows production of estimates that acceptably replicate the actual data and that use of geostatistical procedures may offer advantages in the planning of monitoring systems for marine radioactivity. The use of an oceanographic model was also investigated as a means of assessing the temporal correlation prior to actual sampling, an approach that may offer significant advantages by reducing the need to have lengthy time series prior to designing sampling regimes.

Arctic Regions↗
PubMed2002

Sample size and optimal designs in stratified comparative trials to establish the equivalence of treatment effects among two ethnic groups.

When a new investigational medicine is intended to be applied to populations with different ethnic backgrounds, a stratified comparative phase III trial using ethnic groups as strata may be conducted to assess the influence of ethnic factors on clinical outcomes of this new medicine. In this paper, based on a binomial model with odds ratio as the measure of the treatment effect, we derive the score test and the associated sample size formula for establishing the equivalence/noninferiority of the treatment effects of a medicine among two ethnic groups. A simplified test together with its sample size formula are also given. Taking into account the sample size, cost, and power of testing, respectively, we derive the optimal design parameters, i.e., the allocation among treatment groups and ethnic groups, based on the simplified test.

Algorithms↗
PubMed2002

Risk set sampling for case-crossover designs.

In the case-crossover design, only cases are sampled, and effect estimates are based on within-subject comparisons of exposures at failure times with exposures at control times. Sampling control times appropriately can provide some control for unmeasured confounding, but may introduce bias owing to time trends in the exposure of interest. The theory of risk set sampling (Borgan Ø, Goldstein L, Langholz B. Ann Stat 1995;23:1749-1778) can be used to develop effect estimates in these situations that are free from bias caused by time trends. Through simulation, we compared four sampling schemes: the full-stratum bidirectional design, a matched pair design, the symmetric bidirectional design of Bateson and Schwartz (Bateson T, Schwartz J. Epidemiology 1999;10:539-544), and the semi-symmetric bidirectional design. We also studied a quasi-likelihood extension of Poisson regression with overdispersion. We used daily mean particulate matter less than 10 microm in aerodynamic diameter levels in Denver as the exposure of interest, simulated confounding with linear and seasonal trends, and simulated mortality counts using a log relative risk of 1.1. Neither the matched pair, the full-stratum design, or Poisson regression with overdispersion provided control for seasonal confounding. The symmetric bidirectional design controlled for seasonal confounding but exhibited bias from time trends in exposure. The semi-symmetric bidirectional design provided control of seasonal confounding equal to that of the symmetric bidirectional design, without any time-trend bias.

Air Pollution↗
PubMed1986

Controversies in antimicrobial therapy: critical analysis of clinical trials.

Problems with design and statistical evaluation of clinical efficacy trials of antimicrobial agents are reviewed. Of the three major criteria used for evaluating antimicrobial agents (efficacy, toxicity, cost), the most important is efficacy. Clinical efficacy can be evaluated in uncontrolled or controlled clinical trials. Uncontrolled trials are often conducted to satisfy Food and Drug Administration requirements during premarketing testing; the response rate is typically high because only patients with susceptible infections may be treated and large doses are given. Controlled antibiotic trials should be randomized, blinded, parallel comparisons of an investigational agent versus the best available agent at an accepted dose. However, interpretation of these studies is frequently clouded by poor study design, small sample sizes, and heterogeneous patient populations. Controlled trials are usually centered around a null hypothesis (i.e., that no difference will be found between the agents being compared). All conclusions (to reject or not reject the null hypothesis) should be carefully evaluated by clinicians seeking to apply the available data to patient care. Researchers can incorrectly conclude that two therapies have equal efficacy because of insufficient statistical power (i.e., small sample size) or poor study design. Likewise, researchers may incorrectly conclude that there is a statistical difference between two therapies because of poor design or improper sample selection. For the clinician, clinical relevance takes precedence over statistical significance. Before the results of a study are allowed to affect drug use in an institution, strong similarities between subjects and methods in the study and patients and care in the institution should be demonstrated.

Anti-Bacterial Agents↗
PubMed2004

Sampling household waste at source: lessons learnt in Gaborone.

Municipal solid waste (MSW) quantity and composition analysis is fundamental for the planning of municipal waste management services. The purpose of this paper is to report the results and experiences of sampling household waste at the source of generation in Gaborone, Botswana. The average generation rate, in kg capita(-1) day(-1), and percentages of various components of waste in Gaborone were determined using a statistically designed household sampling survey. The survey covered 47 households with different socio-economic characteristics over 21 days with 893 samples obtained. The results showed that the average waste generation rate for Gaborone was 0.33 kg capita(-1) day(-1). Contrary to common belief, the waste generation rate measured as in weight units was found not be directly related to household income. However, the packaging fractions of plastic and paper measured as volume had a direct relationship with household income. Across all income groups, the putrescible waste fraction constituted the highest proportion of the waste stream at approximately 68%. The main general conclusion is on the importance of practical considerations. As much as statistically designed sampling procedures provide a useful means of estimating the quantity and composition of household waste at source of generation, there are some practical issues that should be carefully considered during sampling to improve the accuracy and relevance of the results.

Botswana↗
PubMedDate not supplied

A new design for large, dilute sample loading in capillary electrophoresis.

In this paper, we report on a new design for a fully in-line sample preconcentration for capillary zone electrophoresis (CZE). It comprises a miniaturized (50-75 microns i.d. x 1 mm) reversed-phase C18 bed (2-4 nL) connected without any dead volume to a CZE capillary. The system permits the fast loading of relatively large sample volumes into the CZE column after elution of the trapped analytes with a small organic solvent volume (20-50 nL). The trapping capacity for peptides was in the high picomole range. No breakthrough or other losses were observed either during microliter-range injections or subsequent washings. The trapped analytes were eluted into the CZE column with less than 50 nL methanol/water (80:2 vol/vol). The narrow band in which samples enter the CZE columns allows direct CZE separation without the necessity of refocusing or stacking. The system performance was studied in relation to the volume and concentration of the leading stacking buffer using electrospray ionization (ESI)-compatible electrolytes. In addition, the system allows fractionation of the trapped analytes using subsequent stronger elutropic elution organic solvent/water mixtures, resulting in a semi-2D separation technique. The system was applied to the analysis of protein digest mixtures and to extremely complex major histocompatibility complex (MHC) class I associated peptides.

Amino Acid Sequence↗