Sources Of Variability In Measurements Research Articles

Evaluation of Measurement System Analysis Techniques for Screw Shaft Manufacturing in Teaching Factory Setting

This study examines the Evaluation of Measurement System Analysis (MSA) Techniques for Screw Shaft Manufacturing in a Teaching Factory Setting at Politeknik STMI Jakarta. The research investigates the precision and accuracy of the measurement system using statistical methods such as Analysis of Variance (ANOVA), Number of Distinct Categories (NDC), and metrics like Total Gauge Repeatability and Reproducibility (GRR), Repeatability, and Reproducibility. Through comprehensive data collection, including multiple appraisers across various trials measured quantitative surveys and qualitative observations, Screw Shaft dimensions and tolerances. The collected data underwent thorough statistical analysis utilizing ANOVA to explore the sources of variation in measurements. The results of the MSA analysis provided critical insights into the measurement system's performance. Repeatability variability (9.97%) and reproducibility variability (3.80%) contribute to a total GRR of 10.67%, indicating an acceptable measurement system. Part-to-part variation emerged as the primary source of variability, emphasizing the importance of addressing part differences in quality control processes. Moreover, ANOVA highlighted the influence of different factors on measurement consistency. Part variations significantly impacted measurement variability, underscoring the need to manage part differences effectively. The assessment of repeatability and reproducibility revealed insights into measurement consistency and reliability. These findings carry significant implications for both industry and education. Understanding the factors affecting measurement variability enables the implementation of corrective measures to enhance product quality and consistency. Additionally, advancements in measurement techniques and quality management practices in Teaching Factory environments contribute to improved product quality and competitiveness in industrial settings. Continued research and evaluation are crucial for further enhancing measurement systems and manufacturing processes.

Estimating Chalkiness in Endosperm of Typical and Bleached Durum Kernels from Transmission Scanned Images

HighlightsDurum wheat kernels were examined using flatbed scanner in transmission mode.Image processing routines were written to determine the %chalkiness per kernel.The distribution of %chalkiness uniquely described market samples.Abstract. The vitreousness of durum samples is regarded by the worldwide wheat industry as an important quality factor for durum shipments. One issue with grading durum occurs on occasional years of unfavorable harvest conditions which result in the kernel outer bran becoming cloudy. Imaging scanners can use either reflective or transmitted lighting. All scanned images of our durum samples were collected using transmissive lighting. Although, “vitreousness” is the usual term applied to durum samples, for this study, “chalkiness” or the inverse property was featured.Both typical and bleached durum kernels were imaged and analyzed. Bleaching seeds has aided grain inspector to visually evaluate the kernels. With computer imaging analysis of bleached kernels, the magnitude of %chalk was significantly attenuated with bleaching verses typical kernels. Still, discrimination of medium and highly chalky kernels was possible with both the typical and bleached seeds.Seed orientation was a source of measurement variability. Seeds were manually and carefully oriented into two distinctly different positions. At the critical lower levels of detection, crease-down orientation may indicate a 100% vitreous seed with the two-dimension view of the scanner, but then 11 of 25 seeds measured some amount of chalkiness when the seed was turned on its side. Furthermore, for seeds with higher amounts of chalkiness, over half of those seeds measured 30% differences.Several durum market samples were provided by Federal Grain Inspection Service and contained levels of non-vitreous seeds for each of three sub-classes of durum: 80%, 65%, 50% vitreous seed. The samples were imaged and analyzed, and chalkiness distributions were plotted. These plots characterize the %chalk for the three classes of wheat. The imaging methods worked satisfactorily for the high and medium levels %chalk per kernel. But the very-low level of chalkiness per kernel proved to be more challenging and was not consistent. Keywords: Grain inspection, HVAC (hard and vitreous kernels of amber color), Image analysis, Vitreousness.

Characterizing Intra-Tumor and Inter-Tumor Variability of Immune Cell Infiltrates in Murine Syngeneic Tumors

Murine tumors are indispensable model systems in preclinical immuno-oncology research. While immunologic heterogeneity is well-known to be an important factor that can influence treatment outcome, there is a severe paucity of data concerning the nature of this heterogeneity in murine tumor models. Using serial sectioning methodology combined with IHC analysis and whole-slide image analysis, the depth-dependent variation in immune-cell abundance in tumor specimens was investigated at single-cell resolution. Specifically, intra- and intertumor variability in cell density of nine immune-cell biomarkers was quantified in multiple murine tumor models. The analysis showed that intertumor variability was typically the dominant source of variation in measurements of immune-cell densities. Statistical power analysis revealed the effect of group size and variance in immune-cell density on the predictive power of detecting a statistically meaningful fold-change in immune-cell density. Intertumor variability in the ratio of immune-cell densities showed distinct patterns in select tumor models and revealed the existence of strong correlations between select biomarker pairs. Furthermore, the relative proportion of immune cells at different depths across tumor samples was preserved in some but not all tumor models, thereby revealing the existence of compositional heterogeneity. Taken together, these results reveal novel insights into the nature of immunologic heterogeneity, which is not accessible through typical omics approaches.

Computational Mapping of the Ground Reflectivity With Laser Scanners.

In this investigation, we focus on the problem of mapping the ground reflectivity with multiple laser scanners mounted on mobile robots/vehicles. The problem originates because regions of the ground become populated with a varying number of reflectivity measurements, whose value depends on the observer and its corresponding perspective. Here, we propose a novel automatic, data-driven computational mapping framework specifically aimed at preserving edge sharpness in the map reconstruction process and that considers the sources of measurement variation. Our new formulation generates map-perspective gradients and applies sub-set selection fusion and de-noising operators to these through iterative algorithms that minimize an l1 sparse regularized least squares formulation. The reconstruction of the ground reflectivity is then carried out based on Poisson's formulation posed as an l2 term promoting consistency with the fused gradient of map-perspectives and a term that ensures equality constraints with reference measurement map data. We demonstrate that our new framework outperforms the capabilities of the existing ones with experiments realized on Ford's fleet of autonomous vehicles. For example, we show that we can achieve map enhancement (i.e., contrast enhancement), artifact removal, de-noising, and map-stitching without requiring an additional reflectivity adjustment to calibrate sensors to the specific mounting and robot/vehicle motion.

English

While the alternative transcription and splicing mechanisms have long been known for some genes like oncogenes, their prevalence in almost all multi-exon genes has been recently realized with the increasing application of high-throughput experimental methods, named Next Generation RNA Sequencing (NGS). Henceforth, understanding the regulation of these processes in comparisons between cell types and cancer requests, sensitive and specific bioinformatics as well as bio-statistic approaches, that is, Cufflinks/Cuffdiff, DEXseq and RESEM, detecting gene transcript/isoforms and exons abundance is necessary. Isoforms and exons expression analysis by NGS is complicated by several sources of measurement variability causing numerous statistical defies. Here, with the purpose of minimizing this statistical challenge, we integrated both Cufflinks/Cuffdiff and DEXseq bioinformatics approaches assessing whole alternative splicing (AS) events, focusing on alternative transcripts regulation and their exons modulation respectively, by processing our previous prepared Estrogen Receptor β (Erβ+ and Erβ-) breast cancer (BC) cells, stimulated by estradiol (E2). Results showed that Estradiol (E2) induced Erβ+ BC (Erβ+E2), exhibited dissimilar reply as opposed to the other’s analyzed BC cell lines in terms of intragenic, exons and junction reads count ratio. Relationship analysis between expressed genes and transcript isoforms, suggested a substantial role of alternative promoters in AS event occurrence in Erβ+ BC as opposed to Erβ- BC. Indeed, merging Cufflinks/Cuffdiff and DEXseq approaches, 79 multi-exon genes were detected as statistically differentially modulated (spliced) in Erβ+ hormone induced BC cell line, and around 38% of these spliced genes claimed to be induced by alternative promoters. The present survey discriminated between several cancer specific alternative splicing genes like LIFR a BC metastasis suppressor, PBX1 a pioneer factor defining aggressive Erβ- BC and PHLPP2 a tumor suppressor, as exhibiting significant exon modulation in early AS occurrence in hormone responsive Erβ+ BC exclusively. Although, our findings supported dissimilar reply comparing both Cuflinks/Cuffdiff and DEXseq approaches called AS events, it is noteworthy to underline their relative agreement, evaluating spliced genes functional annotation as well as their complementarity performing whole AS survey. This study therefore proposed the integration between Cufflinks/Cuffdiff and DEXseq tools as a reasonable complementary methodology assessing full AS pattern in hormone responsive Erβ BC cells. Key words: Cufflinks/Cuffdiff, DEXseq, RNA-Seq, alternative splicing (AS), exons, transcript isoforms, estrogen receptor β (ERβ), breast cancer (BC) cells.

Collaborative guarded-hot-plate tests between the Laboratoire national de métrologie et d’essais and the National Institute of Standards and Technology

A collaborative study to compare the long-term measurement performance between guarded-hot-plate facilities at the Laboratoire national de métrologie et d’essais (LNE) in France and the National Institute of Standards and Technology (NIST) in the United States is presented. Thermal conductivity data were compiled from three international comparisons organized from 1997 to 2014. Measurements were conducted in accordance with standardized test methods (ISO 8302 or ASTM C 177) over a temperature range from 280 K to 320 K. Nine thermal insulating materials (either mineral fiber or expanded polystyrene) were examined covering broad ranges of bulk densities (13 kg · m−3–200 kg · m−3) and thicknesses (13 mm–70 mm). A different set of specimens was utilized for each comparison. Results of this study indicate that, over a 17 year interval, the majority of test data from LNE and NIST agreed to within ±1.0%, or less, for mineral fiber materials and to within ±0.5%, or less, for expanded polystyrene. The long-term variability limit of 1% between the two laboratories is in good agreement with their current measurement uncertainties. Regression coefficients and their standard uncertainties for a straight-line model relating thermal conductivity to temperature from 280 K to 320 K were computed by material and laboratory. Graphical analysis of the data and corresponding fits exhibit consistent behavior by material type between the two laboratories. Sources of measurement variability are addressed.

Clinical precision for follow‐up of glaucoma with PIMD‐2 Pi

PurposeTo estimate sources of variation in measurements of the waist of the retinal ganglion cell axons in the optic nerve head (ONH) over 2π, PIMD‐2π, and the consequences for clinical follow‐up.MethodsThe ONH of each of 18 eyes from 18 glaucoma subjects was imaged 3 times with SD‐OCT (Topcon 3D OCT 2000, Japan, protocol 3D‐Disc cube) at 2 separate occasions within 3 months. PIMD‐2π was segmented 3 times with a custom semi‐automatic algorithm. The magnitude of the variation among occasions, volumes and segmentations was estimated with an analysis of variance. The consequences of the estimated sources of variation for clinical follow‐up was finally modelled, assuming a PIMD‐2π loss rate of 10% of baseline and one segmentation of PIMD‐2π. The significance level was set to 0.05.ResultsThe variance for volumes was estimated to be on the order of 0.3 of the variance for occasions. The variance for segmentation was negligible compared to the variance for volumes. A significant change of PIMD‐2π from baseline can be detected in 1.5–2 years. Increasing the number of visits per year from 1 to 4 substantially improves the detectability of PIMD‐2π change from baseline. More than 4 visits per year does not improve the detectability further. Increasing the number of volumes per visit does not improve detectability.ConclusionsWithin‐subject morphometric estimation of the waist of the retinal ganglion cell axons in the ONH as PIMD‐2π has potential as a useful estimate for follow‐up of glaucoma.

Impact of Pre-analytic Blood Sample Collection Factors on Metabolomics.

Many epidemiologic studies are using metabolomics to discover markers of carcinogenesis. However, limited data are available on the influence of pre-analytic blood collection factors on metabolite measurement. We quantified 166 metabolites in archived plasma from 423 Health Professionals Follow-up Study and Nurses' Health Study participants using liquid chromatography-tandem mass spectrometry (LC-MS). We compared multivariable-adjusted geometric mean metabolite LC-MS peak areas across fasting time, season of blood collection, and time of day of blood collection categories. The majority of metabolites (160 of 166 metabolites) had geometric mean peak areas that were within 15% comparing samples donated after fasting 9 to 12 versus ≥13 hours; greater differences were observed in samples donated after fasting ≤4 hours. Metabolite peak areas generally were similar across season of blood collection, although levels of certain metabolites (e.g., bile acids and purines/pyrimidines) tended to be different in the summer versus winter months. After adjusting for fasting status, geometric mean peak areas for bile acids and vitamins, but not other metabolites, differed by time of day of blood collection. Fasting, season of blood collection, and time of day of blood collection were not important sources of variability in measurements of most metabolites in our study. However, considering blood collection variables in the design or analysis of studies may be important for certain specific metabolites, particularly bile acids, purines/pyrimidines, and vitamins. These results may be useful for investigators formulating analysis plans for epidemiologic metabolomics studies, including determining which metabolites to a priori exclude from analyses. Cancer Epidemiol Biomarkers Prev; 25(5); 823-9. ©2016 AACR.

Image cytometer method for automated assessment of human spermatozoa concentration

In the basic clinical work-up of infertile couples, a semen analysis is mandatory and the sperm concentration is one of the most essential variables to be determined. Sperm concentration is usually assessed by manual counting using a haemocytometer and is hence labour intensive and may be subjected to investigator bias. Here we show that image cytometry can be used to accurately measure the sperm concentration of human semen samples with great ease and reproducibility. The impact of several factors (pipetting, mixing, round cell content, sperm concentration), which can influence the read-out as well as inter-operator and -cytometer variation on two different image cytometers (NC-3000 and SP-100) were evaluated. Furthermore, 725 semen samples were assessed both by manual assessment (WHO recommended method) and by image cytometry and tight correlations between the measured concentrations were shown. Moreover, by evaluation of repeated measurements it appeared that image cytometry produced more consistent and accurate measurements than manual counting of human spermatozoa concentration. In conclusion, image cytometry provides an appealing substitute of manual counting by providing reliable, robust and easy measurement of human sperm concentration.

Differential analysis of gene regulation at transcript resolution with RNA-seq

Differential analysis of gene and transcript expression using high-throughput RNA sequencing (RNA-seq) is complicated by several sources of measurement variability and poses numerous statistical challenges. We present Cuffdiff 2, an algorithm that estimates expression at transcript-level resolution and controls for variability evident across replicate libraries. Cuffdiff 2 robustly identifies differentially expressed transcripts and genes and reveals differential splicing and promoter-preference changes. We demonstrate the accuracy of our approach through differential analysis of lung fibroblasts in response to loss of the developmental transcription factor HOXA1, which we show is required for lung fibroblast and HeLa cell cycle progression. Loss of HOXA1 results in significant expression level changes in thousands of individual transcripts, along with isoform switching events in key regulators of the cell cycle. Cuffdiff 2 performs robust differential analysis in RNA-seq experiments at transcript resolution, revealing a layer of regulation not readily observable with other high-throughput technologies.

Sources of Variability in Measurements of Cardiac Troponin T in a Community-Based Sample: The Atherosclerosis Risk in Communities Study

Application of cardiac troponin T (cTnT) as a marker of myocyte damage requires knowledge of its measurement variability. Using a highly sensitive assay for measurement, we evaluated the long-term storage stability of plasma cTnT at -70 °C and the sources of cTnT variability. Samples from the Atherosclerosis Risk in Communities study collected in 1996-1998 and 2005-2006 were assayed centrally to quantify variability in cTnT attributable to processing (replicates from same blood draw, n = 87), laboratory (replicates after freeze thaw, n = 29), short-term (n = 40) and long-term biological variation (repeat visit, n = 38), and degradation in frozen storage (n = 7677). Approximately 30% of this population-based cohort had cTnT concentrations below the detection limit (3 ng/L). Reliability coefficients for all paired comparisons exceeded 0.93 except for samples drawn 8 years apart (r = 0.36). Sources of cTnT variation (as CVs) were: laboratory, 2.1% and 11.2% in those with and without heart failure, respectively; processing, 18.3%; biological, 16.6% at 6 weeks and 48.4% at 8 years. The reference change value at 6 weeks (68.5%) indicated that 4 samples are needed to determine a homeostatic set point within ±25%. The estimated cTnT degradation rate over the first year in long-term frozen storage was 0.36 ng/L per year. cTnT was detectable in approximately 70% of community-dwelling middle-aged study participants and stable in -70 °C storage. The variability in cTnT attributable to 1 freeze-thaw cycle is of small magnitude. The observed high laboratory and intraindividual (biological) reliability of cTnT support its use for population-based research, and in clinical settings that rely on classification and serial measurements.

Sources of Variability in Measurements of Cardiac Troponin T in a Community-Based Sample: The Atherosclerosis Risk in Communities Study

Sources of Variability in Measurements of Cardiac Troponin T in a Community-Based Sample: The Atherosclerosis Risk in Communities Study

Standardizing the Measurement of Minimum Extinguishing Concentrations of Gaseous Agents

The cup-burner test method has had a long history as a tool for measuring the minimum flame extinguishing concentrations (MEC) of gaseous fire-extinguishing agents for flammable and combustible liquid fuels. The pioneering work by Hirst and Booth (1977) set out the basic principles of the cup-burner and its use. Saso et al. (1993) reported on scale effects on MEC measurement. Preece et al. (2003) reported on parametric effects on MEC measurement. A number of investigators have provided determined values of MEC for a number of inert gas and fluorocarbon agents. See Dlugogorski et al. (1996); Saito et al. (1996); Moore et al. (1998); Sheinson et al. (1998). Takahashi et al. have reported on several investigations of flame extinguishment in the cup-burner including conducting a detailed computational fluid dynamic modeling including reaction kinetics and mass and heat transfer (2003); physical and chemical aspects of flame extinguishment (May 2005); and evaluation of flame extinguishment in low gravity (January 2005). Application of the cup-burner method has, in some instances, produced inconsistent results. MEC values reported by several investigators for the same inert gas agents have exhibited differences that are significant with respect to the way in which they are used (Senecal 2005). Thermochemical analysis and data obtained in a consistent manner suggested that there is a reasonable basis to expect highly consistent, and even predictable, MEC values for inert gas agents. It appeared that the likely source of measurement variation was due to procedural and mechanical differences in the conduct of the cup-burner test among various laboratories. A Task Group, appointed by the NFPA GFE-AAA technical committee on gaseous fire-extinguishing systems, revised the cup-burner test procedure including the specification of a standardized test apparatus. This article describes an inter-laboratory study conducted in 2006 to (1) determine consensus value benchmark minimum extinguishing concentrations (MEC) of an inert gas agent and a halocarbon agent; (2) evaluate the reproducibility of the revised test method; and (3) evaluate the day-to-day consistency (repeatability) of the test method. The results of an inter-laboratory (round robin) study have established benchmark MEC values for nitrogen and HFC-227ea with excellent reproducibility. The results show that MEC values reported by most laboratories were in very good agreement, i.e., exhibited good reproducibility based on averages of three replicate determinations on different days. Analysis of the replicate data revealed a variable degree of repeatability, suggesting that a laboratory will need to review key procedural details in some cases.

Sources of Measurement Variability and Their Effect on the Transfer of near Infrared Spectral Libraries

The use of near infrared spectroscopy for the rapid identification of raw materials has now become widely accepted. In order to facilitate the ease of use of such libraries it is beneficial to be able to transfer libraries from one instrument to another without making any adjustments to the spectral data or the spectral library. Often variability between samples from the same lot, instruments, sampling conditions and environmental conditions impact the performance of a spectral library. These factors also influence the ability to transfer a library or calibration from one instrument to another. To see how large an effect these variables have, a study of various cellulose powders was undertaken to measure the variability resulting from: glass vials, grades of material and lots and instruments, as well as day-to-day variation. It was found that the sources of variation had contributions in the order: material > day-to-day measurements > material lots > vial type > instrument.

Caracterização morfológica de eqüinos da raça Campeiro

Foram utilizados dados de 498 cavalos registrados na Associação Brasileira dos Criadores de Cavalo Campeiro, entre 1985 e 1999. Foram incluídas informações individuais de 16 medidas lineares: alturas da cernelha (AC), do dorso (AD), da garupa (AG), dos costados (ACost) e do vazio subesternal (Vaz); comprimentos da cabeça (CC), do pescoço (CP), do dorso-lombar (CD), da garupa (CG), da espádua (CE) e do corpo (CCorp); larguras da cabeça (LC), do peito (LP) e da anca (LA); perímetros torácico (PT) e de canela (PC). Com os dados de registro, foram calculados o peso (P) e os índices: peitoral (IP), dáctilo-torácico (IDT), corporal (IC), torácico (IT), conformação (ICF), carga para trabalho a trote e a galope (ICG1), carga para trabalho a passo (ICG2), compacidade (ICO1 e ICO2) e relação corporal entre AC e AG (RCG). A análise de variância foi realizada considerando-se os efeitos fixos de mês (MRO) e ano de registro (AR), do sexo, da idade e da cor da pelagem. Os índices obtidos mostraram aptidão intermediária entre trabalho de sela e tração leve. O peso médio foi de 419,96 kg e o IC de 0,849, indicando ser animal mediolíneo, ideal para equitação. A partir do ICG1 e ICG2, estima-se que possa suportar, em média, peso de 117 kg, em trote ou a galope, e 199 kg, em caminhada rápida. Os coeficientes de variação apresentaram grande amplitude, predominando valores baixos. Sexo e cor da pelagem não foram causas importantes de variação nas medidas e nos índices. O MR influenciou CC, CP, CD, CE, LP, LA, PT, PC e a maior parte dos índices. O AR não influenciou AC, AD e ACost, CC, LP e PT, fazendo-o nas demais medidas lineares, mas, entre os índices, teve efeito importante apenas no IT. A idade dos animais influenciou ACost, CD, LC, LP, LA, PT e a maioria dos índices. A cor da pelagem em maior proporção na população foi castanha, seguida por baia e tordilha.

Both Scanning Plane and Observer Affect Measurements of Scaphoid Deformity

The influence of angular deformity of the scaphoid on wrist function and arthrosis is debated and the reliability of the described quantitative measurements of deformity has been questioned. We hypothesized that the inherent imprecision with which computed tomography scanning planes are selected introduces another source of variability in measurements of scaphoid deformity, further diminishing their reliability. Sagittal plane images of 15 computed tomograms of normal scaphoids were evaluated in 3 different reconstruction planes. Four observers measured the lateral intrascaphoid angle, the dorsal cortical angle, and the height-to-length ratio of the 45 images in random order and then measured them again in a distinct random order 2 weeks later. The variability of each observer's measurements (intraobserver reliability) was evaluated with Pearson correlation coefficients. The agreement of the measurements made by the 4 observers (interobserver reliability) and the agreement of the measurements of the same bone in different reconstruction planes (interplane reliability) were evaluated using interclass correlation coefficients. The intraobserver reliability was poor for 27 of 36 comparisons. The interobserver reliability of the dorsal cortical angle and the intrascaphoid angle was poor for all reconstruction planes. The interobserver reliability of the height-to-length ratio was good for 2 planes and poor for the third plane. The interplane reliability was poor for 7 of 12 comparisons, with no single measurement technique remaining consistent for all observers across reconstruction planes. Quantitative measurements of scaphoid deformity have very limited reliability for individual observers, between different observers, and depending on the plane in which the image of the scaphoid is produced. Even the most reliable measure of deformity (height-to-length ratio) was not consistent between reconstruction planes. Unless more reliable scanning and measurement techniques are developed ideas about the effect of scaphoid deformity on wrist function will remain to a large degree speculative.

Achieving high reproducibility isotope ratios with the Cameca IMS 1270 in the multicollection mode

Multicollection system allows improvement of measurement reproducibility for isotope ratios on SIMS instruments provided that the other sources of measurement variability are well controlled. This paper presents analytical protocols developed to control the mass fractionation in the collection optical system and the variation of electron multiplier yield. Results for both silicon and oxygen isotope ratios demonstrate that an experimental error as low 0.2 per mil is achievable whenever both isotopes were measured either with Faraday cup detectors or combining one Faraday cup and one electron multiplier (EM).

Measurement of Sub-Nanometer Lubricant Films Using Ultra-Thin Film Interferometry

The ultra-thin film interferometric method of measuring the thickness of very thin films in lubricated contacts has been refined so as to be able to measure films down to 0.3 nm with a standard deviation of 0.15 nm. The main remaining source of measurement variation for films below 3 nm thick is the surface roughness of the contacting solids. This modified technique has been applied to study the film-forming properties of three fluids, hexadecane, a dilute solution of surfactant in hexadecane, and cyclohexane. Purified hexadecane shows a very slightly enhanced oil-film thickness below 1 nm. The long-chain surfactant forms a boundary film 2 nm thick. Cyclohexane behaves as though it forms a surface layer about 1 nm thick with viscosity three times the bulk fluid viscosity.

Sources of Measurement Variation in Blood Pressure in Large-scale Epidemiological Surveys with Follow-up

The Copenhagen City Heart Study (CCHS) is a longitudinal epidemiological study of 19698 subjects followed up since 1976. Variation in blood pressure (BP) measurement in the first three CCHS surveys is evaluated by assessing two components, systematic variation and random variation [daytime and seasonally variation, observer bias, non-response bias, variation with explanatory variables, such as diabetes, hypertension, body mass index (BMI), height, plasma cholesterol and smoking] for the purpose of identifying relevant errors in population surveys. BP was measured in the seated position after a 5 min rest, with the cuff around the non-dominating arm, in accordance with recommended guidelines. The participation rate fell from 74% in survey 1 to 63% in survey 3. Significant non-response bias with respect to BP values was not found. No daytime variability was noted either in systolic (SBP) or diastolic (DBP) BPs. A trend towards a lower BP was seen during the summertime. Random variation, expressed as the standard deviation of the measured values, increased with increasing BP values (SBP: 11.9-13.4 to 21.2- 25.1 mmHg; DBP: 10.6-11.2 to 11.9-13.4 mmHg). SBP was positively correlated to BMI and plasma cholesterol. SBP was 5-10 mmHg higher in diabetics ( p = 0.000-0.04) than in age- and sex-matched nondiabetics. DBP did not differ between the two groups. Smokers from the age of 50 years had a 2-4 mmHg lower SBP ( p = 0.000-0.01) and 1-3 mmHg lower DBP ( p = 0.000-0.005) than had non-smokers. In addition, significantly fewer smokers took antihypertensive medication than did non-smokers ( p = 0.000). In conclusion, judging from the degree of association with BP and/or differences between the three surveys, the most important factors to consider were seasonal variation, BMI, the use of antihypertensive drug therapy, plasma cholesterol, smoking status and diabetes. An inter-survey comparison of BP in population cohorts requires controlling for these factors.

Assessing sources of variability in measurement of ambient particulate matter

AbstractParticulate matter (PM), a component of ambient air pollution, has been the subject of United States Environmental Protection Agency regulation in part due to many epidemiological studies examining its connection with health. Better understanding the PM measurement process and its dependence on location, time, and other factors is important for both modifying regulations and better understanding its effects on health. In light of this, in this paper, we will explore sources of variability in measuring PM including spatial, temporal and meteorological effects. In addition, we will assess the degree to which there is heterogeneity in the variability of the micro‐scale processes, which may suggest important unmeasured processes, and the degree to which there is unexplained heterogeneity in space and time. We use Bayesian hierarchical models and restrict attention to the greater Pittsburgh (USA) area in 1996. The analyses indicated no spatial dependence after accounting for other sources of variability and also indicated heterogeneity in the variability of the micro‐scale processes over time and space. Weather and temporal effects were very important and there was substantial heterogeneity in these effects across sites. Copyright © 2001 John Wiley & Sons, Ltd.