SEARCH · PubMed Health

Results for “Observer Variation”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,045 records · Page 58Linked to original sources

PubMed1998

Practice styles of US compared to UK neurologists.

OBJECTIVE: This study assessed variation between neurologists in the United States and United Kingdom in their diagnostic and treatment decisions for commonly encountered neurologic presentations, and identified explanatory factors for any observed variation. METHODS: All 210 consultant neurologists in the United Kingdom and a nationally representative sample of 595 US neurologists received mailed surveys containing three detailed clinical scenarios depicting patients with (1) a single unprovoked seizure occurring 3 days previously, (2) early Parkinson's disease, and (3) dementia. The main study outcome measures were self-reported decisions regarding diagnostic test ordering and treatment, which were assessed after each scenario. Neurologists' practice characteristics, certainty about the diagnosis, and attitudes toward uncertainty were also measured. Survey response rates were 92% of US and 63% of UK neurologists. RESULTS: A higher proportion of US than UK neurologists indicated they would order additional diagnostic tests for all three scenarios (all p < 0.05); 77% of UK compared with 26% of US neurologists would manage a single unprovoked seizure without antiepileptic medication (p < 0.0001), but treatment of early Parkinson's disease was not different. Nearly all US and UK neurologists would obtain a neuroimaging study in the evaluation of dementia. International differences persisted after adjustment for differences in demographic and practice characteristics and for attitudes toward test use and clinical uncertainty. CONCLUSIONS: We identified large international variation in clinical decisions across three common neurologic conditions. Cross-country collaboration should explore these differences to develop consensus on standards of care.

Attitude of Health Personnel↗

PubMed2004

Idiopathic arm pain.

BACKGROUND: Arm pain with little or no objective abnormality (referred to herein as idiopathic arm pain) is a common and frustrating problem for both patients and physicians. We investigated the relative effect of idiopathic arm pain and arm pain due to a discrete diagnosis on upper-extremity-specific health status. METHODS: The Disabilities of the Arm, Shoulder and Hand (DASH) questionnaire was completed by 3888 patients seen over a twelve-month period. Scores for the entire sample, for 496 patients diagnosed with idiopathic arm pain, and for 1379 patients diagnosed with one of twenty-one discrete conditions were compared. RESULTS: Patients with idiopathic pain reported substantial and highly variable upper-limb-specific dysfunction (average DASH score [and standard deviation], 36 +/- 24 points). Patients with discrete diagnoses also exhibited substantial variation (average standard deviation, 25; range, 6 to 27) as well as long right tails indicating floor effects, particularly for less severe conditions (Pearson correlation of r = -0.87 between the mean DASH score and skewness). Analysis of variance confirmed the ability of the DASH instrument to discriminate among groups of diagnoses of varying severity, but post hoc Tukey analysis identified ten subgroups with substantial overlap of the DASH scores. CONCLUSIONS: Patients with idiopathic arm pain report substantial and highly variable upper-extremity dysfunction. The wide variations observed in the DASH scores of the patients with idiopathic pain and those with discrete diagnoses are greater than would be expected on the basis of the variations in the objective pathological conditions and may reflect the strong influence of psychological and sociological factors on health status measures.

Arm↗

PubMedDate not supplied

Assessing clot lysis strategies using a simplified mathematical model.

This paper attempts to describe lysis of a clot by infusion of lytic agent using a simple geometrical approach, in which the rate of clot lysis is assumed proportional to the exposed surface of the clot and the concentration of lytic agent. Six simple realizations (a)-(f) of this basic model are developed which account for the dependence of clot lysis time on five different clot geometries. In all six cases the clot is initially described as a uniform cylinder which totally occludes a vessel. In model (a) lysis proceeds as an advancing front at the proximal face of the clot. In model (b) lysis proceeds radially outwards from the central axis of the vessel while in model (c) lysis occurs radially inwards from the surface adjacent the wall, of the cylinder. In models (d) and (e) it is assumed that the clot breaks into a uniform spherical and cylindrical fragments, respectively, while model (f) uses the spherical fragment model combined with a lytic agent concentration which decreases with time. The validity of the models was assessed using previously published data from 76 patients in whom lysis time and clot size were recorded. Least squares linear regression analysis based on the six model equations yielded highly significant correlation coefficients r2 of 0.457, 0.412, 0.412, 0.495, 0.469, 0.663 for models (a)-(f), respectively. The results suggest that when a constant lytic agent concentration is assumed, no single geometry accounts for significantly more variation than any other, but that a combination of varying lytic agent concentration and clot geometry significantly influences clot lysis time and accounts for much of the observed variation.

Humans↗

PubMed1991

Which deprivation? A comparison of selected deprivation indexes.

A number of indexes of deprivation which have been devised or adopted for use by the health services are examined in relation to their performance in explaining the variation observed in a range of health measures, using data for postcode sectors in Scotland. The Scottish deprivation score and the Townsend index are found to explain most variation, and to adhere most closely to the concept of material disadvantage. The Jarman score is less effective as a result of the inclusion of individual variables which are seen to correlate very weakly, even negatively, with the health indicators. The use of these measures in relation to resource allocation and the new GP contract is discussed.

Chronic Disease↗

PubMed1993

Flopping polypeptide chains and Suleika's subtle imperfections: analysis of variations in the electron micrograph of a purple membrane crystal.

Patch averaging, a method of data analysis combining correlation averaging with multivariate statistical analysis, was applied to a high-resolution image of a purple membrane thin crystal. The observed variational patterns fall in two categories: non-crystallographic, related to small electron-optical distortions of the microscope, and crystallographic, conceivably related to variations in the locations of flexible segments of the polypeptide chain on the surface of the membrane.

Bacteriorhodopsins↗

PubMed1995

Components of small area variation in death rates: a method applied to data from Sweden.

STUDY OBJECTIVES: The study aimed to develop and evaluate a method for small area analysis of different non-random components of the variation in death rates. The method was applied to incidence and mortality data for selected malignant neoplasms in 26 administrative health areas in Sweden. DESIGN: Variation in mortality and incidence rates for malignant neoplasms of the trachea, bronchus, and lung; colon; rectum; and cervix uteri in the 26 health areas were analysed after standardisation for age. In addition, the systematic and random components of variance were estimated. The systematic component of variance in mortality was divided into two additive components-one component was dependent on the variation in the corresponding incidence rates and the other remained after adjustment for incidence. SETTING AND PARTICIPANT: All cases diagnosed between 1972 and 1983 and all deaths between 1974 and 1985 for selected malignant neoplasms in Swedish citizens and other residents in Sweden, aged between 0 and 64 years, were analysed. MAIN RESULTS: Much of the observed variation in mortality was explained by the estimated random variation. For malignant neoplasms of the trachea, bronchus, and lung the systematic variation in mortality was mainly explained by the variation in incidence. For cancer of the cervix uteri, alone, there was significant systematic variation of moderate magnitude that was not explained by the incidence rates. CONCLUSIONS: These methods made it possible to divide the observed variance in mortality into different components. Random effects and variance in incidence rates were found to be of great importance when analysing the variance in death rates between health areas. By studying different systematic components of variation it is possible to identify fields for in depth studies on the quality of prevention and treatment.

Adolescent↗

PubMed1985

Size variation of the M protein in group A streptococci.

In addition to the type-specific antigenic variation that is a well-known characteristic for the group A streptococcal M protein, we have now found that the M molecules vary with respect to their molecular size, both between M types and within an M type. By the use of an M6 monoclonal antibody, which crossreacts with 20 different M protein types, and antibodies to the N-acetyl glucosamine determinant of the cell wall, we have been able to identify the M protein molecules released from the streptococcal cell wall with muralytic enzymes, particularly group C phage-associated lysin. Immunoblot analysis of the cell extract identified M protein molecules bound to various cell wall fragments, suggesting a peptidoglycan linkage for the M molecule. M protein extracted from 20 different streptococcal serotypes revealed size variations from 41,000 to 80,000 in molecular weight. This extreme variation is unusual for related proteins. Similar size variations in the M molecule were also found in random clinical isolates of type 6 streptococci. No size change was seen in M6 protein isolated from: (a) strains within a limited epidemic, (b) a strain passaged in mice 192 times, and (c) a strain passaged in the laboratory for 156 generations, suggesting that the observed variation is not a rapid process. The results indicate that, within the broad limits observed in this study, the size of the M protein may not be critical to the antiphagocytic activity of the molecule.

Antigens, Bacterial↗

PubMed1992

Diphytanyl glycerol ether distributions in sediments of the Orca Basin.

Archaebacterially produced diphytanyl glycerol ether (DPGE) was examined in core sediments from the Orca Basin, an anoxic hypersaline basin in the northwestern Gulf of Mexico, to observe its spatial variability and potential origin. A differential extraction protocol was employed to quantify the isopranyl glycerol ethers associated with unbound, intermediate-bound, and kerogen-bound lipid fractions. Archaebacterial lipids were evident at all depths for the unbound and intermediate-bound fractions. Concentrations of DPGE ranged from 0.51 to 2.91 micrograms/g dry sediment at the surface and showed secondary maxima deeper in basin sediments. Intermediate-bound DPGE concentrations exhibited an inverse relationship to unbound DPGE concentrations. Kerogen-bound DPGE concentrations were normally below detection limits. Earlier studies describing the general homogeneity of lipid components within the overlying brine and at the brine/seawater interface suggest that the large-scale sedimentary DPGE variations observed in this study result from spatial and temporal variations in in situ production by methanogenic or extremely halophilic archaebacteria.

Archaea↗

PubMed1999

Variation between experienced observers in the interpretation of accident and emergency radiographs.

Skill mix and role extension initiatives have highlighted the difficulty of establishing quality standards for the accuracy of plain film reporting. An acceptable performance might be one which is indistinguishable from that of a group of experienced consultant radiologists. In order to assess the feasibility of setting such a standard, the variation between experienced observers must first be established. This study examines the variation found between three observers with the three major types of plain film examination. 402 plain film examinations (205 skeletal, 100 chest and 97 abdominal) performed on accident and emergency patients were reported retrospectively and independently by three experienced radiologists. The clinical data supplied on the request cards were available to the readers. Each examination was categorized by each reader as being normal, as showing significant abnormality relevant to the current clinical problem, or as showing insignificant or irrelevant abnormality. Concordance between all three readers was found in 51%, 61% and 74% of abdominal, chest and skeletal radiographs, respectively. Weighted kappa values confirmed that the level of agreement between pairs of observers was higher with skeletal radiographs (kappa w = 0.76-0.77) than with chest (kappa w = 0.63-0.68), or abdominal (kappa w = 0.50-0.78) examinations. However, the frequency of major disagreements (at least one reader reporting "normal" and one reporting "relevant abnormality") was similar for abdominal (11%), chest (12%) and skeletal (10%) radiographs. When the reports were reclassified into only two groups--either significantly abnormal or not--pairs of observers disagreed on 9-10% of skeletal, 11-19% of chest and 8-18% of abdominal cases. The average incidence of errors per observer was estimated to be in the range 3-6%. The magnitude of interobserver variation in plain film reporting is considerable, and must be taken into account when designing assessment techniques and setting quality standards for this activity.

Bone and Bones↗

PubMed2006

Plasma concentrations of plant sterols: physiology and relationship with coronary heart disease.

Recently, it has been questioned whether elevated levels of circulating plant sterols increase the risk of coronary heart disease (CHD). To date, no definitive conclusions regarding such a relationship have been reached, nor have there been any studies summarizing the factors that contribute to the observed elevations in plant sterol concentrations in plasma. Thus, the purpose of this review is to systematically compare the plant sterol levels of subjects from the general population and to describe factors that contribute to the variations observed. The question of whether elevated plasma concentrations of plant sterols are associated with an increased risk of CHD was also assessed. Results indicate that the key factors accounting for variations in circulating plant sterol concentrations include: apolipoprotein E phenotypes, ATP-binding cassette transporter polymorphisms, use of statin drugs, presence of metabolic syndrome, dietary intake of plant sterols, gender, and analytical techniques used in the measurement of plant sterols in the plasma. An analysis of the studies examining the relationship between circulating levels of plant sterols and CHD risk in non-sitosterolemic populations revealed no clear associations. Furthermore, it was shown that the above-mentioned factors play an important role in determining the levels of plant sterols in plasma. Since these factors may act as potential confounders, they must be controlled for before more solid conclusions can be reached.

ATP Binding Cassette Transporter, Subfamily G, Mem↗

PubMed1996

Apolipoprotein E genotype determines survival in the oldest old (85 years or older) who have good cognition.

OBJECTIVE: To quantify the influence of apolipoprotein E (APOE) polymorphism on cognition and survival in a population sample aged 75 years or older. DESIGN: The Kungsholmen Project established a cohort of 1810 residents in a district in Stockholm, Sweden, aged 75 years or older in 1987. Information on cognition at cohort inception is available for all subjects. Subjects were followed up for mortality to January 1, 1995. SUBJECTS: Included in this study are 1077 subjects (of 1124 genotyped for APOE) with the common epsilon 2/3, epsilon 3/3, and epsilon 3/4 APOE genotypes. RESULTS: The odds of cognitive impairment for the epsilon 3/4 vs epsilon 3/3 genotype declined with age: 4.8 for age 75 through 79 years; 1.7 for age 80 through 84 years; and 1.0 (i.e., no association) for age 85 years or older. Despite this association, APOE polymorphism did not significantly predict survival in subjects younger than 85 years, nor did it predict survival in subjects 85 years or older who were cognitively impaired. Instead, survival varied fourfold with respect to APOE polymorphism in those 85 years or older who had good cognition: Mortality in subjects with the epsilon 2/3 genotype was half that in those who carried the epsilon 3/3 genotype (hazard ratio, 0.5; 95% confidence interval, 0.2 to 0.9), and mortality in subjects with the epsilon 3/4 genotype was twice that in those who carried the epsilon 3/3 genotype (hazard ratio, 2.0; 95% confidence interval, 1.1 to 3.5). This fourfold variation resulted in 2-year differences in survival. CONCLUSIONS: The minor sequence variation in the apolipoprotein E isoforms resulted in a fourfold difference in the risk of death among the oldest old (age > or = 85 years) with good cognition. The observed variation in mortality was unlikely to have been caused by cognitive impairment, as APOE polymorphism was not a risk factor for cognitive impairment in this age group.

Age Factors↗

PubMed2002

Paternal occupational group and risk of offspring with neural tube defects.

Selected paternal occupations as well as specific occupational exposures to chemicals such as organic solvents have been suggested as possible risk factors for neural tube defects (NTD). We investigated data from a population-based, case-control study of fetuses and liveborn infants with NTDs among 1989-91 California births and fetal deaths. Interviews were conducted with mothers of 538 NTD cases and 539 non- malformed controls. Mothers were asked to report the occupations that the fathers had in the period 3 months before and 3 months after conception. Each job title and industry reported was coded in accordance with the 1990 US Census. Considering those fathers who worked in managerial and professional occupations as the reference group, elevated odds ratios (OR) for NTDs were observed for the categories: technical, sales and administrative, OR = 1.5 [95% confidence interval 1.0, 2.4]; service, OR = 2.0 [1.2, 3.1]; farming, forestry and fishing, OR = 2.1 [1.3, 3.3]; operators, fabricators and labourers, OR = 1.8 [1.2, 2.7]; and military, OR = 1.9 [0.7, 5.0]. Stratification by NTD phenotype revealed that these elevated ORs were primarily observed for spina bifida phenotypes. Analyses adjusted for maternal body mass index, maternal periconceptional use of multivitamins containing folic acid, paternal race/ethnicity, maternal race/ethnicity and maternal education revealed attenuated risk estimates for most of the occupational groups. Analyses of 182 more specific occupational groups defined by aggregating fathers on similar job titles, when compared with fathers who worked in managerial and professional occupations, revealed that four job title groups were associated with fairly precise effect estimates of >or=1.5. These groups were: cooks; janitors and cleaners; farm workers; and groundsmen/gardeners. Using occupational titles as defined in previous investigations, we did not observe an elevated OR associated with paternal occupational solvent exposures, OR = 0.8 [0.5, 1.3]. These analyses generated potential clues regarding paternal occupational exposures as NTD risk factors. Risk variation observed by spina bifida phenotype is interesting and will need to be investigated further.

Anencephaly↗

PubMed2005

Biological variation between two Brazilian geographical isolates of Echinostoma paraensei.

The biological behaviour and morphometric data from two allopatric isolates of Echinostoma paraensei (Rio Bonito - RB and Sumidouro - SU) collected from naturally infected Nectomys squamipes from two secluded Atlantic Forest fragments were studied. Mice that had been experimentally infected with ten encysted metacercariae of each isolate were monitored weekly in two trials to analyse worm burden and the kinetics of worm distribution along the intestine. The total number of uterine eggs, wet weights and measurements of the worms and body, acetabulum, testes and ovaries were also analysed. The RB isolate showed a higher worm burden, 7.7+/-0.8, and a longer life span, 16 weeks, compared to a worm burden of 5.8+/-1.1 and life span of 9 weeks for the SU isolate. Worms of the RB isolate were clustered in the duodenum and in the bile duct while the SU isolate worms were dispersed along the small intestine of infected mice. Both isolates developed similarly as regards morphometric data and wet weight, although the total number of uterine eggs was greater in RB. The degree of intraspecific variation observed in the worm distribution along the intestine, worm burden and life span raises questions regarding the use of these criteria for species differentiation. These findings suggest that variation in biological parameters found between the E. paraensei isolates could result from geographical isolation and, in particular, the environmental conditions of transmission. Further studies on E. paraensei polulations from different forest fragments will contribute towards an understanding of the speciation of this parasite.

Animals↗

PubMed2002

Variations in adult body mass in roe deer: the effects of population density at birth and of habitat quality.

Body mass is a key determinant of fitness components in many organisms, and adult mass varies considerably among individuals within populations. These variations have several causes, involve temporal and spatial factors, and are not yet well understood. We use long-term data from 20 roe deer cohorts (1977-96) in a 2600 ha study area (Chizé, western France) with two habitats contrasting in quality (rich oak forest in the North versus poor beech forest in the South) to analyse the effects of both cohort and habitat quality on adult mass (i.e. median body mass between 4 and 10 years of age) of roe deer (Capreolus capreolus). Cohort strongly influenced the adult body mass of roe deer in both sexes: males born in 1994 were 5.2 kg heavier when aged between 4 and 10 years old than males born in 1986, while females born in 1995 were 4.7 kg heavier between 4 and 10 years old than females born in 1982. For a given cohort, adult males were, on average, 0.9 kg heavier in the rich oak forest than in the poor beech forest. A similar trend occurred for adult females (0.5 kg heavier in the oak forest). The effects of cohort and habitat were additive and accounted for ca. 40% of the variation observed in the adult mass of roe deer at Chizé (males: 41.2%; females: 40.2%). Population density during the spring of the birth accounted for about 35% of cohort variation, whereas rainfall in May-June had no effect. Such delayed effects of density at birth on adult body mass probably affect population dynamics, and might constitute a mechanism by which delayed density-dependence occurs in ungulate populations.

Analysis of Variance↗

PubMed2005

Dissociation analysis in polymerase chain reaction and 1X SSC buffer as a prerequisite for selection of 13mer microarray probe sets with uniform hybridization behavior.

Homogeneous probe hybridization is a prerequisite for the robust design of microarrays. Elaborate algorithms were developed to select for probe sets with uniform melting temperatures (Tm). However, at least short oligonucleotides (< 20 bp) show large variation in the on-chip hybridization efficiency even if designed with state-of-the-art algorithms. This variation can be explained by steric effects and interferences on the solid surface as well as by chemical conditions that may deviate from conditions used to develop the algorithms. We designed 412 random 13mer duplexes to study the differences between the Tm of nearest-neighbor algorithms and the Tm values measured by dissociation analysis in polymerase chain reaction (PCR) and 1X SSC buffer. We tested the effects of theoretical vs empirical Tm values on the hybridization variation of 40 duplexes on-chip. Although the empirical approach resulted in a slightly better prediction of hybridization efficiency, less than one-fifth (17%) of the observed variation could be explained by the factor Tm alone. We conclude that state-of-the-art algorithms can be used for a first selection of short oligonucleotide probes, but that it is then necessary to perform an on-chip selection to obtain a probe set with a uniform hybridization behavior.

Algorithms↗

PubMedDate not supplied

The low skull base: an invitation to disaster.

BACKGROUND: Knowledge of anatomy including variations observed with endoscopy or computerized tomography scan is vital to the performance of safe endoscopic sinus surgery. The lower-than-normal skull base/cribriform plate is an anatomic variation, which if not noted preoperatively, can lead to entrance into the brain causing major injury. METHODS: Four case studies of chronic rhinosinusitis are reviewed in which either the whole anterior skull base or the cribriform plate is lower than usual and major complications occurred. RESULTS: All four cases had unilateral or bilateral entrance into the skull base/cribriform plate of the brain in the biopsy specimen, postoperative cerebrospinal fluid leak, and/or brain hemorrhage. One patient died from the injury, three patients had marked neurological sequelae. The low skull base and its meaning for the surgeon is discussed at length. CONCLUSION: The preoperative anatomy as determined by endoscopy and computerized tomography scanning has to be identified. Variations or abnormalities should be noted and taken into consideration for preoperative and operative planning. Failure to note skull base or cribriform anatomy variations may lead to brain entrance, injury, and death.

Adult↗

PubMed1995

Effects of propranolol compared with clonidine on portal haemodynamics: a double-blind cross-over study using duplex-Doppler ultrasonography.

BACKGROUND: Patients with liver cirrhosis and large oesophageal varices run a high risk of digestive haemorrhage due to the rupture of oesophageal varices, an event associated with a high mortality. At present, the only treatment for the prevention of first bleeding from oesophageal varices on which there is general agreement is drug-based. In order to tailor drug treatment to the requirements of individual patients more precisely, an ever-increasing number of drugs is being investigated. DESIGN: Double-blind cross-over study. METHODS: Sixteen cirrhotic patients with large oesophageal varices were studied by means of duplex-Doppler ultrasonography to determine variations in portal haemodynamics after oral administration of 0.150 mg clonidine and to compare these with the variations observed after oral administration of 40 mg propranolol. RESULTS: Propranolol caused a significant reduction in maximum portal flow velocity (P < 0.001), whereas clonidine failed to cause any such variation (P = 0.194). Considering as responders those patients who exhibited at least a 10% decrease in maximum portal flow velocity, 11 patients responded to propranolol; of these, three also responded to clonidine. No patient responded only to clonidine. CONCLUSION: The absence of any effects on the parameters of portal haemodynamics would appear to deny clonidine any significant role in preventing first bleeding resulting from the rupture of oesophageal varices.

Administration, Oral↗

PubMed2000

Genetic divergence among Venezuelan populations of Lutzomyia longipalpis (Diptera: Psychodidae: Phlebotominae).

Lutzomyia longipalpis (Lutz & Neiva) is the primary vector of visceral leishmaniasis in Venezuela. An analysis of alleles at seven enzyme-encoding loci among four populations from different geographic and epidemiological regions revealed strong genetic substructuring. Isozyme analysis indicated that L. longipalpis in Venezuela is a complex of at least two subspecies. Possible differences in population size during their evolutionary histories, varying colonization histories and geological events may explain discrepancies in the patterns of variation observed at genetic markers between these four populations.

Animals↗