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PubMed2001

Sample-sample and wavenumber-wavenumber two-dimensional correlation analyses of attenuated total reflection infrared spectra of polycondensation reaction of bis(hydroxyethyl terephthalate).

Polycondensation reaction of bis(hydroxyethylterephthalate) was monitored in situ by attenuated total reflection (ATR)/infrared (IR) spectroscopy. The obtained spectra are analyzed by means of generalized two-dimensional (2D) sample-sample and wavenumber-wavenumber correlation spectroscopies. The sample-sample correlation analysis reveals the correlations among the concentration features of the components, and the wavenumber-wavenumber correlation analysis elucidates the relations among the spectral features. Before the experimental data are analyzed by the 2D correlation spectroscopies, a synthetic two-component spectral model composed of the first and the last experimental spectra, is examined. The results of an analysis of the real data are related to those obtained from the synthetic data. It is found that the sample-sample correlation analysis of the IR data of polycondensation explains the concentration variance in the system and classifies two groups of the samples. The wavenumber-wavenumber correlations are derived upon the results of the sample-sample correlations and explained in terms of the spectral variations of three components. The convolute patterns in both types of correlations are attributed to the weak presence of ethylene glycol.

Journal Article↗
PubMed2002

Collection, storage, and filtration of in vivo study samples using 96-well filter plates to facilitate automated sample preparation and LC/MS/MS analysis.

The benefits of high-throughput bioanalysis within the pharmaceutical industry are well established. One of the most significant bottlenecks in bioanalysis is transferring in vivo-generated study samples from their collection tubes during sample preparation and extraction. In most cases, the plasma samples must be stored frozen prior to analysis, and the freeze/thaw (F/T) process introduces thrombin clots that are capable of plugging pipets and automated liquid-transfer systems. A new approach to dealing with this problem involves the use of Ansys Captiva 96-well 20-microm polypropylene filter plates to collect, store frozen, and filter plasma samples prior to bioanalysis. The samples are collected from the test subjects, and the corresponding plasma samples are placed directly into the wells of the filter plate. Two Duoseal (patent pending) covers are used to seal the top and bottom of the plate, and the plate is stored at down to -70 degrees C. Prior to sample analysis, the seals are removed and the plate is placed in a 96-well SPE manifold. As the plasma thaws, it passes (by gravity or mild vacuum) through the polypropylene filter into a 96-well collection plate. A multichannel pipet or automated liquid-transfer system is used to transfer sample aliquots without fear of plugging. A significant advantage of this approach is that, unlike other methods, issues related to incomplete pipetting are virtually eliminated. The entire process is rapid since thawing and filtering take place simultaneously, and if a second F/T cycle is required for reanalysis, it is not necessary to refilter the samples (additional clotting was not observed after three F/T cycles). This technique was tested using monkey, rat, and dog plasma and sodium heparin and EDTA anticoagulants. To assess the possibility of nonspecific binding to the polypropylene filter, a variety of drug candidates from diverse drug classes were studied. Validation data generated for two Lilly compounds from distinct classes, before and after filtering, are presented in this paper as practical examples of this technique. While LC/MS/MS is the primary method of bioanalysis in our laboratory, the technique presented in this paper is applicable to other forms of detection as well.

Autoanalysis↗
PubMed1997

Automated on-line sample pretreatment system for the determination of trace metals in biological samples by inductively coupled plasma mass spectrometry.

A fully automated on-line sample pretreatment system combining microwave digestion with sample preconcentration/matrix separation for the determination of trace metals (Fe, Ni, Cu, Zn, and Pb) in blood and serum samples by inductively coupled plasma mass spectrometry (ICPMS) was designed and evaluated. The samples were mixed with an appropriate reagent and digested in a flow-through, focused microwave-heated oven. After digestion, the sample solution was transferred on-line to a column packed with iminodiacetate-based resin for separation of matrix elements like Na, K, Ca, Mg, Cl, P, and S that might interfere with the measurement by ICPMS. The analytes chelated on the resin were subsequently eluted and led to ICPMS for multielement determination. The whole sample pretreatment process was automatically controlled by a self-designed expert system. The analytical reliability of data from this on-line system was confirmed to be good with the analysis of SRM samples (Seronorm Whole Blood and NIST SRM 1598 Bovine Serum), and the limits of detection (3 sigma) for Fe, Ni, Cu, Zn, and Pb were 68, 0.34, 3.5, 13.4, and 0.22 microgram/L, respectively. With this fully automated on-line system, the determination of analytes in biological fluid samples down to micrograms-per-liter levels has been proven to be feasible, and the sample throughput can achieve up to 6 samples/h.

Animals↗
PubMed1998

A sample purification method for rugged and high-performance DNA sequencing by capillary electrophoresis using replaceable polymer solutions. B. Quantitative determination of the role of sample matrix components on sequencing analysis.

In the previous paper, a sample cleanup procedure for DNA sequencing reaction products was developed, in which template DNA was removed by ultrafiltration and the total concentration of salts (chloride and di- and deoxynucleotides) was decreased below 10 microM using gel filtration. In this paper, a quantitative study of the effects of these sample solution components on the injected amount and separation efficiency of the sequencing fragments in capillary electrophoresis is presented. The presence of chloride and deoxynucleotides in a total concentration above 10 microM in the sample solution significantly decreased the amount of DNA sequencing fragments injected into the capillary column. However, the separation efficiency was not affected upon increasing the amount of salt. On the other hand, in the presence of only 0.1 microgram of template in the sample (one-third of the lowest quantity recommended in cycle sequencing) and at very low chloride concentration (approximately 5 microM), the separation efficiency decreased by 70%, and the injected amount of DNA sequencing fragments was 40% lower compared to the sample cleaned by the new purification method. The deleterious effect of template DNA on the separation of sequencing fragments was suppressed in the presence of salt in a concentration above 100 microM in the sample solution. Separately, it was found that both the electric field strength and duration of injection affected the resolution of DNA sequencing fragments when the cleaned up sample solution was used. Separation efficiencies of 15 x 10(6) theoretical plates/m were achieved when the sample was loaded at low electric field, e.g., 25 V/cm for 80 s or less. The results demonstrate that the sample solution components (chloride, deoxynucleotides, template DNA) and injection conditions must be controlled to achieve high performance and rugged DNA sequencing analysis.

Chlorides↗
PubMedDate not supplied

Population sampling in European air pollution exposure study, EXPOLIS: comparisons between the cities and representativeness of the samples.

A personal air pollution exposure study, EXPOLIS, was accomplished in six European cities among 25- to 55-year-old citizens. In order to compare the exposure results and different microenvironmental concentrations between the cities it is crucial to know the extent and effects of the population bias that has developed in sampling procedure and the sociodemographic characteristics of each measured population sample. In each participating city a random Base sample of 2000 to 3000 individuals was drawn from the census and a Short Questionnaire (SQ) was mailed to them. Two subsamples of the Respondents of the mailed questionnaire were randomly drawn: Diary sample for 48-h time--microenvironment--activity diary and extensive exposure questionnaires, and Exposure sample for the same plus personal exposure and microenvironmental monitoring. Significant differences existed between the EXPOLIS cities in the population-sampling procedure. Population-sampling bias was evaluated by comparing the Respondents with the total city populations. The share of women and individuals with more than 14 years of education is higher among the Respondents than the overall population except in Athens. Men, younger (25-34 years old) and unmarried individuals were hardest to get to participate in the study at least in Helsinki. The two subsamples differ from Respondents in having more employed and higher- educated individuals. The largest sample bias occurred at the first and easiest step of responding to the mailed Short Screening Questionnaire, and not at the last and most demanding stage of participating in the exposure measurements. Exposure data from some of EXPOLIS cities can only be compared to other cities with caution considering their large population bias or different sample selections. However the selection bias is not necessarily a problem for analyses about predictors of personal exposures or analyses within a city.

Adult↗
PubMed2006

Vacuum sampling techniques for industrial hygienists, with emphasis on beryllium dust sampling.

The U.S. Department of Energy (DOE) Chronic Beryllium Disease Prevention Program Rule, 10 CFR Part 850 became effective in 2000 in response to the prevalence of Chronic Beryllium Disease (CBD) in workers. The rule requires surface and air monitoring for beryllium to determine exposure levels and the evaluation of the effectiveness of controls used to minimize or eliminate that risk. The most common methods for surface sampling use wet or dry wipes. Wipe sampling techniques may be impractical for many surfaces common to most buildings such as cinder block, textured wall surfaces, fabric and carpet. Vacuum sampling methods have been developed for the evaluation of lead or pesticides on residential surfaces such as carpets, bare floors and window sills. However, the current vacuum methods may be impractical for many workplace situations such as sampling of protective clothing, complex facility structures, or equipment surfaces. Recent work using vacuum sampling for potential bio-terrorism agents such as anthrax spores may have significant application to industrial hygiene evaluations of the workplace and may be extendable for use in sampling of metals such as beryllium. Validated vacuum sampling methods that provide meaningful data would be of great value to industrial hygienists in identifying areas having surface contamination, evaluating existing controls and work practices and determining the potential of toxic material on surfaces to become airborne and present a potential risk to workers and the public. This article discusses various vacuum sampling methodologies and recommends harmonization of sampling methods.

Beryllium↗
PubMed1997

Evaluation of single sample clearance calculations in 902 patients. A comparison of multiple and single sample techniques.

PURPOSE: To derive new formulae for the calculation of single sample clearance of the contrast medium iohexol and to compare the formulae to a selection of existing single sample clearance formulae derived for the calculation of 51Cr-EDTA and 99mTc-DTPA clearance. MATERIAL AND METHODS: Glomerular filtration rate (GFR) was calculated from total plasma clearance of iohexol used for urography in 902 patients. Two plasma samples were drawn in each patient. Automated x-ray fluorescence analysis equipment was used for the plasma iodine analysis. Single and multiple sample iohexol clearance values were compared. In 77 patients the multiple sample clearance values were additionally compared to a 51Cr-EDTA clearance performed simultaneously or within 14 days. RESULTS: The precision of the results calculated by the existing single sample clearance formulae and the derived iohexol single sample clearance formulae were essentially the same. The most precise of the derived formulae was that based on the Bak Christensen & Groth formula. The correlation between multiple sample clearance of iohexol and 51Cr-EDTA was high (r = 0.918). CONCLUSION: Iohexol can substitute 51Cr-EDTA for GFR measurement. A valid GFR can be calculated from a single plasma sample determination of iohexol clearance using either the existing formulae or the new formulae derived from the present study.

Adolescent↗
PubMed2001

Development of sampling and analytical methods for concerted determination of commonly used chloroacetanilide, chlorotriazine, and 2,4-D herbicides in hand-wash, dermal-patch, and air samples.

Sampling and analytical methods were developed for commonly used chloroacetanilide, chlorotriazine, and 2,4-D herbicides in hand washes, on dermal patches, and in air. Eight herbicides selected for study were alachlor, atrazine, cyanazine, 2,4-dichlorophenoxyacetic acid (2,4-D), metolachlor, simazine, and two esters of 2,4-D, the 2-butoxyethyl ester (2,4-D, BE) and the 2-ethylhexyl ester (2,4-D, EH). The hand-wash method consisted of shaking the worker's hand in 150 mL of isopropanol in a polyethylene bag for 30 seconds. The dermal-patch method entailed attaching a 10-cm x 10-cm x 0.6-cm polyurethane foam (PUF) patch to the worker for exposure; recovery of the herbicides was achieved by extraction with 40 mL of isopropanol. The air method involved sampling with an OVS-2 tube (which contained an 11-mm quartz fiber filter and two beds of XAD-2 resin) and recovery with 2 mL of 10:90 methanol:methyl t-butyl ether. Analysis of each of the three sample types was performed by gas chromatography with an electron-capture detector. Diazomethane in solution was employed to convert 2,4-D as the free acid to the methyl ester in each of the three methods for ease of gas chromatography. Silicic acid was added to sample solutions to quench excess diazomethane. Limits of detection for all eight herbicides were matrix-dependent and, generally, less than 1 microgram per sample for each matrix. Sampling and analytical methods met NIOSH evaluation criteria for all herbicides in hand-wash samples, for seven herbicides in air samples (all herbicides except cyanazine), and for six herbicides in dermal-patch samples (all herbicides except cyanazine and 2,4-D). Speciation of 2,4-D esters and simultaneous determination of 2,4-D acid were possible without losses of the esters or of other herbicides (acetanilides and triazines) being determined.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1992

Evaluation of high volume particle sampling and sample handling protocols for ambient urban air mutagenicity determinations.

An investigation of high volume particle sampling and sample handling procedures was undertaken to evaluate variations of protocols being used by the U.S. Environmental Protection Agency. These protocols are used in urban ambient air studies which collect ambient and source samples for subsequent mutagenicity analysis of the organic extracts of the aerosol fraction. Specific protocol issues investigated include: (a) duration of sampling period, (b) type of filter media used to collect air particles, (c) necessity for cryogenic field site storage and dry ice shipping of filter samples, and (d) sample handling at the receiving laboratory. Six PM10 Hi-Vol samplers were collocated at an urban site in downtown Durham, North Carolina and operated simultaneously to evaluate 12 h versus 24 h collection periods and filter media choices of glass fiber, Teflon impregnated glass fiber (TIGF), and quartz fiber. Filters from the samplers plus field blanks were collected during each of 25 sampling periods. TIGF filters from two samplers were immediately placed on dry ice in the field and transported directly to cryogenic storage. TIGF, quartz, and glass fiber filters from three samplers were transported at ambient and maintained at room temperature for three to six days prior to cryogenic storage. One TIGF sample, which was collected on a previously tared filter, was subjected to controlled environment equilibration (40 percent relative humidity, 22 degrees C) for 8 to 24 h and weighed prior to cryogenic storage. All filters were subsequently stored at -70 degrees C to -80 degrees C prior to a one-time extraction and Salmonella (Ames) mutagenicity bioassay of the entire sample set.(ABSTRACT TRUNCATED AT 250 WORDS)

Air Pollutants↗
PubMed1994

Bioaerosol sampling in field studies: can samples be express mailed?

Bioaerosol sampling for viable microorganisms was conducted in 25 dairy barns in summer and in winter to examine the relationship of sample storage and shipping in determining bioaerosol concentrations separately for yeasts, molds, mesophilic bacteria, and thermophilic organisms. The study also compared the performance of three sampling methods--(1) all-glass impinger (AGI) used with peptone solution in both seasons and (2) betaine solution in winter; and (3) the nuclepore filtration and elution (NFE) method, using air filtration with subsequent elution and culturing--which were studied in a pairwise fashion with duplicate, simultaneous, side-by-side sampling. For each sample, one duplicate was analyzed within two hours in a laboratory less than 50 km from the sampling site, while the other was express-mailed to the authors' laboratory. Concentrations of all microorganisms measured by the AGI peptone method were unaffected by mailing in winter, but mesophilic bacteria increased in summer. AGI betaine samples were unchanged except for increased concentrations of molds after mailing in winter. Yeasts and mesophilic bacteria significantly decreased after mailing of NFE samples. Pairwise comparison of the sampling methods in winter yielded no significant differences in airborne concentrations for the yeasts, mesophilic bacteria, and thermophilic bacteria. Both AGI betaine and NFE methods had significantly greater concentrations of molds than AGI peptone. In summer, concentrations of yeasts and mesophilic bacteria were significantly greater with AGI peptone, as were molds with the NFE method.(ABSTRACT TRUNCATED AT 250 WORDS)

Air Pollutants, Occupational↗
PubMed1983

An evaluation of soil sampling for 137Cs using various field-sampling volumes.

The sediments from a liquid effluent receiving area at the Los Alamos National Laboratory and soils from an intensive study area in the fallout pathway of Trinity were sampled for 137Cs using 25-, 500-, 2500- and 12,500-cm3 field sampling volumes. A highly replicated sampling program was used to determine mean concentrations and inventories of 137Cs at each site, as well as estimates of spatial, aliquoting, and counting variance components of the radionuclide data. The sampling methods were also analyzed as a function of soil size fractions collected in each field sampling volume and of the total cost of the program for a given variation in the radionuclide survey results. Coefficients of variation (CV) of 137Cs inventory estimates ranged from 0.063 to 0.14 for Mortandad Canyon sediments, whereas CV values for Trinity soils were observed from 0.38 to 0.57. Spatial variance components of 137Cs concentration data were usually found to be larger than either the aliquoting or counting variance estimates and were inversely related to field sampling volume at the Trinity intensive site. Subsequent optimization studies of the sampling schemes demonstrated that each aliquot should be counted once, and that only 2-4 aliquots out of as many as 30 collected need be assayed for 137Cs. The optimization studies showed that as sample costs increased to 45 man-hours of labor per sample, the variance of the mean 137Cs concentration decreased dramatically, but decreased very little with additional labor.

Cesium Radioisotopes↗
PubMed2005

LENTICULE discs provide a homogenous format for external quality assessment samples: a comparison with freeze-dried samples for shellfish microbiology.

AIMS: The aim was to compare the variability in Escherichia coli enumeration data and detection of Salmonella spp. between four samples of LENTICULE discs and freeze-dried samples for the Health Protection Agency's External Quality Assessment (EQA) scheme for shellfish microbiology. METHODS AND RESULTS: Four samples of known but undisclosed microbiological content were dispatched in both freeze-dried and LENTICULE disc formats to 57 participating laboratories in 20 countries. Participants examined samples using their routine methods for the most probable number (MPN) of E. coli per 100 g and the presence/absence of Salmonella spp. There was no significant difference between the Food and Environmental Proficiency Testing Unit and participating laboratories for E. coli and Salmonella spp. results. There were significantly less outlying results using the LENTICULE discs than freeze-dried sample format and equivalent or less variance for the former for E. coli MPN. There was no significant difference between LENTICULE discs and freeze-dried samples for the presence/absence of Salmonella spp. CONCLUSIONS: Overall the results indicated that there was equivalent or less variance in results for the LENTICULE discs than for freeze-dried samples, therefore LENTICULE discs are a homogenous and stable matrix for EQA samples. SIGNIFICANCE AND IMPACT OF THE STUDY: This study provides validation data for the replacement of freeze-dried samples by LENTICULE discs for the Health Protection Agency Shellfish EQA Scheme.

Animals↗
PubMed2026

Comparative evaluation of probe-capture and conventional metagenomic sequencing across multiple clinical sample types, with analysis of paired bronchoalveolar lavage fluid and blood samples.

Conventional metagenomic next-generation sequencing (mNGS) suffers from host nucleic acid interference and poor performance in low-biomass samples. Probe-capture metagenomic sequencing (PC-mNGS), which enriches microbial targets via hybridization probes, shows superior sensitivity but lacks systematic multi-sample evaluations. This study compared PC-mNGS and mNGS across diverse clinical specimens (bronchoalveolar lavage fluid [BALF], blood, cerebrospinal fluid [CSF]) and assessed the clinical utility of pathogen co-detection in paired BALF-blood samples from sepsis patients. A total of 282 samples (81 BALF, 141 blood, 25 CSF, 35 others) sequenced by both PC-mNGS and mNGS were analyzed. Additionally, 621 paired BALF-blood samples from sepsis patients with pulmonary infections were evaluated. PC-mNGS achieved higher pathogen detection rates (66.67% vs 57.10%, P = 0.000198) than mNGS, particularly in blood (66.67% vs 47.52%, P = 2.5 × 10⁻⁵). PC-mNGS detected more bacteria (19 species exclusive) and fungi (11 species exclusive) than mNGS. Viruses showed comparable detection. BALF and CSF exhibited high overall agreement (OPA: 96.30% and 88%, respectively), while blood had lower concordance (NPA: 54.05%, OPA: 70.92%). A total of 60.55% of BALF-positive samples (PC-mNGS) had co-detected pathogens in blood. Gram-negative bacteria (e.g., Klebsiella pneumoniae) and fungi (e.g., Candida albicans) showed higher blood co-detection rates than viruses. In this study, PC-mNGS detected more pathogens and showed a higher positivity rate than mNGS in blood samples. BALF sequencing data, particularly bacterial reads per million (RPM), may predict bloodstream co-detection, aiding in sepsis management. However, clinical validation and integration with traditional diagnostics are needed to confirm utility. This study highlights PC-mNGS as a promising tool for complex infections but underscores the need for rigorous multi-context validation.IMPORTANCEAccurate and rapid identification of pathogens is critical for effective treatment of severe infectious diseases, such as sepsis. This study demonstrates that probe-capture metagenomic sequencing (PC-mNGS) detected more pathogens in blood samples compared to conventional metagenomic sequencing, especially for bacterial and fungal infections. By analyzing paired lung and blood samples, we show that high pathogen levels in lung fluid may predict bloodstream infection, offering a potential early warning for clinicians. These findings support the use of PC-mNGS as a more sensitive diagnostic tool, which could lead to faster, more targeted therapies and better outcomes for patients with complex infections.

Humans↗
PubMed2006

Vaginal self sampling versus physician cervical sampling for HPV among younger and older women.

OBJECTIVES: To estimate the agreement between self collected vaginal swabs and physician collected cervical brush samples for detection of oncogenic human papillomavirus infection (HPV) by the hybrid capture 2 (HC-2) test among women younger and older than 50 years, and to assess women's preference for sample collection method based on age. METHODS: Consecutive women aged 15-49 years due for a 1 year visit in a prevalence study of carcinogenic HPV and a new sample of women aged 50 years and older attending their family physicians for cervical screening, in Ontario, Canada, performed vaginal self sampling and underwent physician cervical sampling and cervical cytology. Women completed a self administered questionnaire on demographics and preference for sampling method. RESULTS: Among the 307 women aged 15-49 years, the prevalence of HPV was 20.8% (64/307) and 17.6% (54/307) in the vaginal and cervical specimens, respectively. Among the women aged 50 years and older, prevalence was 9.9% (15/152) and 8.6% (13/152), respectively. Kappa for agreement between sample collection methods was 0.54 for the younger and 0.37 for the older women (both p< 0.001). Nearly half of the women preferred self sampling or had no preference. CONCLUSIONS: There was fair agreement between self collected vaginal and physician collected cervical specimens for detecting carcinogenic HPV in younger and older women. Vaginal sampling for HPV appears to be promising as a primary screening strategy for cervical cancer prevention programmes in low resource settings in developed and developing countries.

Adolescent↗
PubMed2004

Sub-sampling and preparing forensic samples for pollen analysis.

The main forensic application of palynology is in providing associative evidence, assisting to prove or disprove a link between people and objects with places or with other people. Although identification and interpretation of pollen is a specialist job, sub-sampling and preparing pollen samples for analysis may be carried out by non-specialists. As few forensic laboratories have residing palynologists, laboratories may wish to reduce the cost of analysis or risk of contamination by doing their own sub-sampling and preparation. Presented is a practical guide for sub-sampling and preparing forensic samples for pollen analysis, providing a complete standard procedure for both the palynologist and non-specialist. Procedures for sub-sampling include a wide variety of materials commonly collected for forensic analysis (soil, clothing and other fabrics, footwear, twine and rope, firearms, granulated materials, plant and animal material, and illicit drugs), many of which palynologists will not be familiar with. Procedures for preparation of samples (pollen concentration) are presented as a detailed, step-by-step method. Minimizing the risks of laboratory and cross-sample contamination during sub-sampling and preparation is emphasized.

Animals↗
PubMed1995

Nuclear morphometry in breast cancer: the influence of sampling rules and freezing of samples.

We studied nuclear morphometry of human breast cancer with special emphasis on two sources of variation: freezing prior to fixation and selection of measured objects on the basis of different sampling rules. Samples of 147 histologically verified invasive breast cancer cases were examined with a computer-based image overlay drawing system. Thirty-eight of the 147 samples of tissue frozen before embedding in paraffin were analyzed separately. Among the latter we found shrinkage of 35% and 46% (depending on the sampling rule) of the nuclear profile area as compared with samples not frozen before the standard tissue processing. These findings confirm that nuclear morphometry results from frozen and unfrozen tissue are not comparable. Frozen tissue later embedded in paraffin should not be used with prognostication models based on traditionally fixed tissue. In morphometry we applied two sampling rules that differed in the criteria used for selecting nuclei for measurement. We registered a significant difference in nuclear size and in the variation of nuclear size between the two sampling methods. Of the morphometric features studied, nuclear area was affected most. Finally, we examined the two sampling rules in light of the established prognosticators in breast cancer: tumor size, axillary lymph node status, and the Multivariate Prognostic Index (MPI). The two sampling rules resulted in different distributions of morphometric results in the prognostic groups. Our findings emphasize the significance of the sources of variation in nuclear morphometry. They also stress the need for well-standardized morphometric methods in predicting the outcome of breast cancer.

Breast Neoplasms↗
PubMed2005

Using lot quality-assurance sampling and area sampling to identify priority areas for trachoma control: Viet Nam.

OBJECTIVE: To report on the use of lot quality-assurance sampling (LQAS) surveys undertaken within an area-sampling framework to identify priority areas for intervention with trachoma control activities in Viet Nam. METHODS: The LQAS survey method for the rapid assessment of the prevalence of active trachoma was adapted for use in Viet Nam with the aim of classifying individual communes by the prevalence of active trachoma among children in primary school. School-based sampling was used; school sites to be sampled were selected using an area-sampling approach. A total of 719 communes in 41 districts in 18 provinces were surveyed. FINDINGS: Survey staff found the LQAS survey method both simple and rapid to use after initial problems with area-sampling methods were identified and remedied. The method yielded a finer spatial resolution of prevalence than had been previously achieved in Viet Nam using semiquantitative rapid assessment surveys and multistage cluster-sampled surveys. CONCLUSION: When used with area-sampling techniques, the LQAS survey method has the potential to form the basis of survey instruments that can be used to efficiently target resources for interventions against active trachoma. With additional work, such methods could provide a generally applicable tool for effective programme planning and for the certification of the elimination of trachoma as a blinding disease.

Child↗
PubMed2006

Modeling motor vehicle crashes using Poisson-gamma models: examining the effects of low sample mean values and small sample size on the estimation of the fixed dispersion parameter.

There has been considerable research conducted on the development of statistical models for predicting crashes on highway facilities. Despite numerous advancements made for improving the estimation tools of statistical models, the most common probabilistic structure used for modeling motor vehicle crashes remains the traditional Poisson and Poisson-gamma (or Negative Binomial) distribution; when crash data exhibit over-dispersion, the Poisson-gamma model is usually the model of choice most favored by transportation safety modelers. Crash data collected for safety studies often have the unusual attributes of being characterized by low sample mean values. Studies have shown that the goodness-of-fit of statistical models produced from such datasets can be significantly affected. This issue has been defined as the "low mean problem" (LMP). Despite recent developments on methods to circumvent the LMP and test the goodness-of-fit of models developed using such datasets, no work has so far examined how the LMP affects the fixed dispersion parameter of Poisson-gamma models used for modeling motor vehicle crashes. The dispersion parameter plays an important role in many types of safety studies and should, therefore, be reliably estimated. The primary objective of this research project was to verify whether the LMP affects the estimation of the dispersion parameter and, if it is, to determine the magnitude of the problem. The secondary objective consisted of determining the effects of an unreliably estimated dispersion parameter on common analyses performed in highway safety studies. To accomplish the objectives of the study, a series of Poisson-gamma distributions were simulated using different values describing the mean, the dispersion parameter, and the sample size. Three estimators commonly used by transportation safety modelers for estimating the dispersion parameter of Poisson-gamma models were evaluated: the method of moments, the weighted regression, and the maximum likelihood method. In an attempt to complement the outcome of the simulation study, Poisson-gamma models were fitted to crash data collected in Toronto, Ont. characterized by a low sample mean and small sample size. The study shows that a low sample mean combined with a small sample size can seriously affect the estimation of the dispersion parameter, no matter which estimator is used within the estimation process. The probability the dispersion parameter becomes unreliably estimated increases significantly as the sample mean and sample size decrease. Consequently, the results show that an unreliably estimated dispersion parameter can significantly undermine empirical Bayes (EB) estimates as well as the estimation of confidence intervals for the gamma mean and predicted response. The paper ends with recommendations about minimizing the likelihood of producing Poisson-gamma models with an unreliable dispersion parameter for modeling motor vehicle crashes.

Accidents, Traffic↗