Naturalistic study designs in samples with refractory pain: advantages and limitations.
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Clinical Trials as Topic↗
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Detecting environmental impacts on the Mediterranean seagrass Posidonia oceanica (L.) Delile: the use of reconstructive methods in combination with 'beyond BACI' designs.
Interannual changes in leaf production and rhizome elongation rates of the seagrass Posidonia oceanica have been evaluated by means of reconstructive methods at the Travello meadow (Ligurian Sea, NW Mediterranean, Italy) to provide evidence of responses to the putative impact of a beach replenishment made with terrigenous materials in 1993. Two additional meadows (Genoa-Quinto and Noli) were sampled as controls. An asymmetrical sampling design ('beyond BACI': Before/After, Control/Impact) was thus used to detect the impact on the basis of a single sampling as dating methods obviated the lack of pre-impact data. At all three meadows investigated, leaf production and rhizome elongation rates were reconstructed for 12 previous years (from 1988 to 1999). A marked decrease in the leaf production rate (around 20%) was assessed only at Travello immediately after the putative disturbance. Control meadows, instead, did not display any significant variations in the pattern of change of this variable from before to after the putative impact. With regard to rhizome growth rates, no significant changes in space and time attributable to the putative impact have been detected. The present data also suggest that the impact studied may be considered as a pulse disturbance, since leaf production appeared to recover over a comparatively short-time scale (around 2-3 years) if compared to the low turn-over and high longevity of P. oceanica. The high potential of asymmetrical sampling designs in combination with dating methods is discussed in the light of the results presented here.
Journal Article↗
Summary statements of the NIH Nursing Research Grant Applications.
Summary statements from the Nursing Research Study Section, Division of Research Grants, NIH, between October, 1986 and June, 1988 were used to identify reasons for recommending approval or disapproval of grant applications with RO1 and R29 activity codes. The 917 comments (25 +/- 4 per critique), sorted into one of nine categories (Aims, Significance, Investigator, Budget, Resources, Design, Sample, Techniques, Data Analysis) for analysis, were classified as Strengths (positive comments) or Weaknesses (negative comments). The weaknesses of approved applications were confined mostly to the categories of Design and Techniques. Disapproved applications had few strengths and many weaknesses in Design, Sample, Techniques, and Data Analysis. Critiques of First Award (R29) and traditional research project grant applications (RO1) were similar. The approved applications addressed meaningful problems, had well-synthesized literature reviews, and were solvable by available techniques. The research plans were consonant with stated aims, and the methods sections reflected understanding of the principles underlying the techniques to be used. A supportive environment and adequate research resources, including access to the study population were common to these applications. Disapproved applications provided poor synthesis of the literature, methods inconsistent with the aims, and often reflected inadequate understanding of techniques to be used.
Humans↗
Cigarette smoking among low-income African Americans: a serious public health problem.
BACKGROUND: This study examines the current prevalence of cigarette smoking and the number of cigarettes smoked in a community-based sample of 1021 low-income African-American men and women. METHODS: Participants were selected using a two-stage, area probability sample design. Data were collected in 2002-2003 in face-to-face interviews and analyzed in 2005. All data and analyses were weighted to account for the complex sampling design. RESULTS: Fifty-nine percent of men and 41% of women were current smokers, with younger individuals apparently initiating smoking at an earlier age than older individuals. CONCLUSIONS: The high prevalence of cigarette use provides further evidence that the excess burden of tobacco-related disease among low-income African-American families may be on the rise. This is of great concern, and if confirmed by further research, indicates an urgent need for preventive intervention.
Adolescent↗
Antioxidant supplementation of boar spermatozoa from different fractions of the ejaculate improves cryopreservation: changes in sperm membrane lipid architecture.
Previous studies have shown sperm quality after cryopreservation differs depending on the fraction of seminal plasma the boar spermatozoa are contained in. Thus, spermatozoa contained in the first 10 ml of the sperm-rich fraction (portion I) withstand handling procedures (extension, handling and freezing/thawing) better than those contained in the latter part of a fractionated ejaculate (second portion of the sperm-rich fraction and the post-spermatic fraction; portion II). The present study evaluated whether an exogenous antioxidant, the water-soluble vitamin E analogue Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), could, when added to the freezing extender in a split-sample design trial, improve the post-thaw viability and membrane quality of this particular portion of the ejaculate, with particular attention to the status of the plasma membrane. Using a split-sample design, the initial changes in the fluidity status of the sperm plasmalemma after thawing were measured by flow cytometry (FC) after loading with Merocyanine-540 and YO-PRO-1. The FC-derived data revealed a clear ejaculate portion-dependent effect of the antioxidant supplementation. While no beneficial effect of the antioxidant supplementation was visible in spermatozoa from portion I, more spermatozoa with intact membranes were observed in the supplemented samples of portion II, suggesting the protective effect of vitamin E is dependent of the portion of the boar ejaculate considered.
Animals↗
Estimating the incidence of dementia from two-phase sampling with non-ignorable missing data.
Two-phase sampling designs have been used in the field of psychiatry to estimate prevalence and incidence of a rare disease such as dementia and Alzheimer's disease. In a longitudinal study on dementia, since the repeated two-phase sampling is conducted several years after the baseline wave, some subjects may die before the follow-up wave, thus their disease status prior to death is missing. There are reasons to suggest that the missing due to death is non-ignorable. Estimation of disease incidence from longitudinal dementia study has to appropriately adjust for data missing by death as well as the sampling design used at each study wave. In this paper we adopt a selection model approach to model the missing data by death and use a likelihood approach to derive incidence estimates. A modified EM algorithm is used to deal with data from sampling selection. The non-parametric jack-knife variance estimator is used to derive variance estimates for the model parameters and the incidence estimates. The proposed approaches are applied to data from the Indianapolis-Ibadan Dementia Study.
Black or African American↗
Lot quality assurance sampling (LQAS) for monitoring leprosy elimination in an endemic district in Tamilnadu.
This paper examines whether the health administration can use lot quality assurance sampling (LQAS) for identifying high prevalence areas for leprosy for initiating necessary corrective measures. The null hypothesis was that leprosy prevalence in the district was at or above ten per 10,000 and the alternative hypothesis was that it was at or below five per 10,000. A total of 25,500 individuals were to be examined with 17 as an acceptable maximum number of cases (critical value). Two-stage cluster sample design was adopted. The sample size need not be escalated as the estimated design effect was 1. During the first phase, the survey covered a population of 4,837 individuals out of whom 4,329 (89.5%) were examined. Thirty-five cases were detected and this number far exceeded the critical value. It was concluded that leprosy prevalence in the district should be regarded as having prevalence of more than ten per 10,000 and further examination of the population in the sample was discontinued. LQAS may be used as a tool by which one can identify high prevalence districts and target them for necessary strengthening of the programme. It may also be considered for certifying elimination achievement for a given area.
Cluster Analysis↗
Linked surveys of health services utilization.
The linked population/establishment survey (LS) of health services utilization is a two-phase sample survey that links the sample designs of the population sample survey (PS) and the health-care provider establishment sample survey (ES) of health services utilization. In Phase I, household respondents in the PS identify their health-care providers during a specified calendar period. In Phase II, health-care providers identified in Phase I report the variables of interest for all or a sample of their transactions with all households during the same calendar period. The LS has been proposed as a potential design alternative to the PS whenever the health-care transactions of interest are hard to find or enumerate in household surveys and as a potential design alternative to the ES whenever it is infeasible or expensive to construct or maintain complete sampling provider frames that list all health-care providers with good measures of provider size. Suppose that the non-sampling errors are ignorable, how do the LS, PS and ES sampling errors compare? This paper addresses that question by summarizing and extending recent research findings that compare expressions of the sampling variance of (1) the LS and PS of equivalent household sample size and (2) the LS and the ES of equivalent expected health-care provider and transaction sample sizes. The paper identifies the parameters contributing to the precision differences and assesses the conditions that favour the LS or one or the other surveys. Published in 2007 by John Wiley & Sons, Ltd.
Data Interpretation, Statistical↗
New method for surname studies of ancient patrilineal population structures, and possible application to improvement of Y-chromosome sampling.
Several studies showed that surnames are good markers to infer patrilineal genetic structures of populations, both on regional and microregional scales. As a case study, the spatial patterns of the 9,929 most common surnames of the Netherlands were analyzed by a clustering method called self-organizing maps (SOMs). The resulting clusters grouped surnames with a similar geographic distribution and origin. The analysis was shown to be in agreement with already known features of Dutch surnames, such as 1) the geographic distribution of some well-known locative suffixes, 2) historical census data, 3) the distribution of foreign surnames, and 4) polyphyletic surnames. Thus, these results validate the SOM clustering of surnames, and allow for the generalization of the technique. This method can be applied as a new strategy for a better Y-chromosome sampling design in retrospective population genetics studies, since the idenfication of surnames with a defined geographic origin enables the selection of the living descendants of those families settled, centuries ago, in a given area. In other words, it becomes possible to virtually sample the population as it was when surnames started to be in use. We show that, in a given location, the descendants of those individuals who inhabited the area at the time of origin of surnames can be as low as approximately 20%. This finding suggests 1) the major role played by recent migrations that are likely to have distorted or even defaced ancient genetic patterns, and 2) that standard-designed samplings can hardly portray a reliable picture of the ancient Y-chromosome variability of European populations.
Chromosomes, Human, Y↗
Development of an optimal sampling strategy for clinical pharmacokinetic studies of the novel anthracycline disaccharide analogue MEN-10755.
AIM: MEN-10755 is a novel anthracycline analogue that has shown an improved therapeutic efficacy over doxorubicin in animal models, especially in gynaecological and lung cancers and is currently under clinical development for the treatment of solid tumours. The aim of the project was to develop an optimal sampling strategy for MEN-10755 to provide an efficient basis for future pharmacokinetic/pharmacodynamic investigations. METHODS: Data from 24 patients who participated in a phase I clinical pharmacokinetic study of MEN-10755 administered as a short i.v. infusion were included. Individual pharmacokinetic values were calculated by fitting the plasma concentration data to a two-compartment model using nonlinear least-squared regression (KINFIT, Ed 3.5). Population pharmacokinetic analysis was carried out using (a) the traditional standard two-stage method (STS) based on all data (KINFIT-ALL), (b) the iterative two-stage Bayesian (IT(2)B) population modelling algorithm (KINPOP), and (c) the STS method using KINFIT and using four optimally timed plasma concentrations (KINFIT-OSS4). Determinant (D) optimal sampling strategy (OSS) was used to evaluate the four most information-rich sampling times. The pharmacokinetic parameters V(c) (l), k(el) (h(-1)), k(12) (h(-1)) and k(21) (h(-1)) calculated using KINPOP served as a model for calculation of four D-optimal sampling times. D-optimal sampling data sets were analysed using KINFIT-OSS4 and compared with the population model obtained by the traditional standard two-stage approach for all data sets (KINFIT-ALL). RESULTS: The optimal sampling times were: the end of the infusion, and 1.5 h, 3.8 h and 24 h after the start of the infusion. The four-point D-optimal sampling design determined in this study gave individual parameter estimates close to the basic standard estimates using the full data set. CONCLUSION: Because accurate estimates of pharmacokinetic parameters were achieved, the four-point D-optimal sampling design may be very useful in future studies with MEN-10755.
Algorithms↗
Randomized, controlled trial of phototherapy for neonatal hyperbilirubinemia. Development, design, and sample composition.
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Birth Weight↗
Detectability in conventional and adaptive sampling.
In this paper a simple but very general method is given for estimating a population total with any sampling design when objects in sampled units are observed with imperfect detectability--a problem characteristic of many surveys of natural and human populations. In the most general case, the method consists of dividing the value of the variable of interest associated with each detected object by the detection probability for that object and then proceeding to use the estimation method that would ordinarily be used under the design if there were no detectability problems. Examples illustrating the method include simple random sampling, conventional unequal probability sampling, and adaptive cluster sampling.
Analysis of Variance↗
Estimating risk and rate levels, ratios and differences in case-control studies.
Classic (or 'cumulative') case-control sampling designs do not admit inferences about quantities of interest other than risk ratios, and then only by making the rare events assumption. Probabilities, risk differences and other quantities cannot be computed without knowledge of the population incidence fraction. Similarly, density (or 'risk set') case-control sampling designs do not allow inferences about quantities other than the rate ratio. Rates, rate differences, cumulative rates, risks, and other quantities cannot be estimated unless auxiliary information about the underlying cohort such as the number of controls in each full risk set is available. Most scholars who have considered the issue recommend reporting more than just risk and rate ratios, but auxiliary population information needed to do this is not usually available. We address this problem by developing methods that allow valid inferences about all relevant quantities of interest from either type of case-control study when completely ignorant of or only partially knowledgeable about relevant auxiliary population information.
Cardiovascular Diseases↗
Utility of sparse concentration sampling for citalopram in elderly clinical trial subjects.
The objective of this study was to evaluate whether the disposition of the selective serotonin reuptake inhibitor, citalopram, could be robustly captured using 1 to 2 concentration samples per subject in 106 patients participating in 2 clinical trials. Nonlinear mixed-effects modeling was used to evaluate the pharmacokinetic parameters describing citalopram's disposition. Both a prior established 2-compartment model and a de novo 1-compartment pharmacokinetic model were used. Covariates assessed were concomitant medications, race, sex, age (22-93 years), and weight. Covariates affecting disposition were assessed separately and then combined in a stepwise manner. Pharmacokinetic characteristics of citalopram were well captured using this sparse sampling design. Two covariates (age and weight) had a significant effect on the clearance and volume of distribution in both the 1- and 2-compartment pharmacokinetic models. Clearance decreased 0.23 L/h for every year of age and increased 0.14 L/h per kilogram body weight. It was concluded that hyper-sparse sampling designs are adequate to support population pharmacokinetic analysis in clinically treated populations. This is particularly valuable for populations such as the elderly, who are not typically available for pharmacokinetic studies.
Administration, Oral↗
Application of random effects to the study of resource selection by animals.
1. Resource selection estimated by logistic regression is used increasingly in studies to identify critical resources for animal populations and to predict species occurrence. 2. Most frequently, individual animals are monitored and pooled to estimate population-level effects without regard to group or individual-level variation. Pooling assumes that both observations and their errors are independent, and resource selection is constant given individual variation in resource availability. 3. Although researchers have identified ways to minimize autocorrelation, variation between individuals caused by differences in selection or available resources, including functional responses in resource selection, have not been well addressed. 4. Here we review random-effects models and their application to resource selection modelling to overcome these common limitations. We present a simple case study of an analysis of resource selection by grizzly bears in the foothills of the Canadian Rocky Mountains with and without random effects. 5. Both categorical and continuous variables in the grizzly bear model differed in interpretation, both in statistical significance and coefficient sign, depending on how a random effect was included. We used a simulation approach to clarify the application of random effects under three common situations for telemetry studies: (a) discrepancies in sample sizes among individuals; (b) differences among individuals in selection where availability is constant; and (c) differences in availability with and without a functional response in resource selection. 6. We found that random intercepts accounted for unbalanced sample designs, and models with random intercepts and coefficients improved model fit given the variation in selection among individuals and functional responses in selection. Our empirical example and simulations demonstrate how including random effects in resource selection models can aid interpretation and address difficult assumptions limiting their generality. This approach will allow researchers to appropriately estimate marginal (population) and conditional (individual) responses, and account for complex grouping, unbalanced sample designs and autocorrelation.
Animals↗
Effective field sampling for predicting the spatial distribution of reindeer (Rangifer tarandus) with help of the Gibbs sampler.
We describe an approach to estimation of the spatial distribution of reindeer (Rangifer tarandus). Spatial autocorrelation, inherent to the data describing the distribution of wildlife species, contains information that can be utilized to improve the effciency of field inventories. Our data included reindeer fecal pellet counts, satellite imagery and a digital terrain model. We applied ordinary logistic regression, autologistic regression, and the Gibbs sampler to predict spatial distribution of reindeer based on the combined data. A training set was used to compare the outcome for different field sampling designs for each method. Results suggested the possibility to reduce the number of plots by up to 75% with a 15% reduction in prediction accuracy (quality). We also showed that the Gibbs sampler outperformed, in terms of accuracy, the logistic regression. The outcome, however, was dependent on the spectral homogeneity of the area and on the relative position of the sampling design to the elevation curves. Our results justify the incorporation of spatial information when modeling the distribution of reindeer at finer scales (< 1 km).
Animals↗
The significance of relatedness and gene flow on population genetic structure in the®subsocial spider Eresus cinnaberinus (Araneae: Eresidae)
Interdemic selection, inbreeding and highly structured populations have been invoked to explain the evolution of cooperative social behaviour in the otherwise solitary and cannibalistic spiders. The family Eresidae consists of species ranging from solitary and intermediate subsocial to species exhibiting fully cooperative social behaviour. In this study we, in a hierarchical analysis, investigated relatedness of putative family clusters, inbreeding and population genetic structure of the subsocial spider Eresus cinnaberinus. Five hierarchical levels of investigation ranging from large scale genetic structure (distances of 250 and 50 km level 1 and 2) over microgeographic structure (20 km2 and 4 km2, level 3 and 4) to a single hill transect of 200 m (level 5) were performed. The purpose of level 5 was two-fold: (1) to investigate the relatedness of putative family groups, and (2) to evaluate the influence of both family living and sampling design on higher level estimates. Relatedness estimates of putative family groups showed an average relatedness of R=0.26. There was no indication of inbreeding. In contrast to social spiders, genetic variation was abundant, Heapproximately0.10. The population genetic structure was intermediate between social and asocial spiders. Genetic variance increased continually across hierarchical levels. Family structured neighbourhoods biased differentiation estimates among level 5 samples (FST=0.04) and level 3 and 4 samples (0.07 0, was caused by disjunct sampling from separate neighbourhoods. Larger scale samples were highly differentiated 0.12<FST<0.26, depending on level and sampling design. Due to a distance effect family living did not influence estimates of the higher level 1. Although the dispersing sex among social spiders and the subsocial E. cinnebarinus differ, females versus males, female behaviour of both sociality classes lead to high genetic variance.Copyright 1998 The Linnean Society of London
Journal Article↗
A study of disruptive behavior disorders in Puerto Rican youth: I. Background, design, and survey methods.
OBJECTIVE: This is the first of two related articles on a study carried out between 2000 and 2003 designed to assess the prevalence, associated comorbidities, and correlates of disruptive behavior disorders in two populations of Puerto Rican children: one in the Standard Metropolitan Areas of San Juan and Caguas in Puerto Rico, and the other in the south Bronx in New York City. METHOD: This article provides the study's background, design, and methodology. Probability samples of children ages 5 to 13 years were drawn at the two sites (n = 2,491). Subjects and their primary caretakers were interviewed using the Diagnostic Interview Schedule for Children-IV and a wide array of risk factor measures. The samples were weighted to correct for differences in the probability of selection resulting from sample design and to adjust for differences from the 2000 U.S. Census in the age/gender distribution. RESULTS: The samples are representative of the populations of Puerto Rican children in the south Bronx and in the Standard Metropolitan Areas in Puerto Rico. Of the 2,940 children identified as eligible for the study, 2,491 participated for an overall compliance rate of 85%. CONCLUSIONS: The study results, to be described in an accompanying report, are generalizable to the two target populations.
Adolescent↗