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Results for “Observer Variation”

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PubMed1992

Assessment of outcome in patients with low-back pain.

The Low-Back Outcome Score has been devised as a new and accurate rating system for patients with low-back pain. Thirteen factors, such as pain, employment, sporting ability, rest required, and activities of daily living, were included; subjective opinion was excluded. Pain and active pursuits were weighted. Presentation of the score as a questionnaire, excluding examination findings, eliminated both interobserver variation and observer variation with time. The score was applied retrospectively in a follow-up study of conservatively treated patients and was found to be more comprehensive and more discriminating than the Oswestry Disability Score, the Waddell Disability Rating, or the Waddell Physical Impairment Rating. The Low-Back Outcome Score is recommended for further evaluation in future prospective studies in low-back pain.

Back Pain↗

PubMed2000

Mating preference functions of individual female barking treefrogs, Hyla gratiosa, for two properties of male advertisement calls.

A mating preference function describes the relationship between variation in a trait in potential mates and the strength of the preference for that trait. Few studies have measured mating preference functions either at a population level or for individuals. We used two-choice playback experiments to determine the mating preference functions of individual female barking treefrogs for two call characteristics: call-repetition rate and fundamental frequency. We tested each female four times with each pair of stimuli and with three to six pairs of stimuli. Individual females exhibited directional preferences for higher call rates and stabilizing preferences for intermediate fundamental frequency. These individual preference functions were similar to population-level preferences documented in previous studies. Within a stimulus type (call rate or fundamental frequency), nearly all females exhibited the same general preference function. However, females varied in the minimum difference between stimuli necessary to elicit a unanimous choice for the higher call rate, and they differed in both the intermediate fundamental frequency they preferred most and the minimum difference in fundamental frequency that elicited a unanimous choice for one of the two alternatives. The variation we observed among females was not repeatable; repeatabilities were in general low and statistically nonsignificant. The observed variation in the preferences of females, even if unrepeatable, should weaken selection on male traits relative to selection in the absence of such variation.

Animals↗

PubMed2001

Variation in general esterase activity within a population of Haematobia irritans (Diptera: Muscidae).

Control of the horn fly, Hematobia irritans (L.), is generally dependent on chemical insecticides. However, the biology and behavior of the horn fly favors rapid development of insecticide resistance. To prolong the effectiveness of the insecticide option, information is required regarding the mechanisms of insecticide resistance. Metabolic hydrolysis of insecticides by esterases is a detoxification mechanism in many insect species. Measurement of general esterase activity within populations of horn flies may provide a diagnostic tool for resistance management. In this study we evaluated the amount of variation in general esterase activity within female and male horn fly samples from a population that had not been exposed to insecticides for 8 yr. We found considerable variation in general esterase activity within samples of each sex, with females demonstrating the greater variation. The observed variation is thought to be the result of age-structure dynamics within the population. The amount of inherent variation makes it difficult to detect small mean differences between populations, thus limiting the utility of general esterase assays. Thus, effective diagnosis of esterase-mediated resistance mechanisms can only be achieved by the identification of specific detoxification esterases and the design of assays, either biochemical or molecular, for their detection and measurement.

Aging↗

PubMed2005

Confirmation of Gnathostoma binucleatum Almeyda-Artigas, 1991, advanced third-stage larvae in Tres Palos Lagoon, Mexico, by morphological and molecular data.

Advanced third-stage larvae of Gnathostoma sp. corresponding to 6 morphotypes, distinguished on the basis of the shape of the cephalic hooklets, were collected from the muscle tissue of 5 species of freshwater fish (i.e., Dormitator latifrons, Eleotris picta, Gobiomorus maculatus, Ariopsis guatemalensis, and Cichlasoma trimaculatum) in Tres Palos Lagoon, Guerrero, Mexico. Principal components analysis of 4 morphological characters cluster all samples in a single taxonomic group. A minimum amount of variation was observed among ITS2 sequences of 3 morphotypes and Gnathostoma binucleatum obtained from GenBank (0-0.84%). The observed variation among morphotypes 1, 2, and 3 is the result of intraspecific variability of G. binucleatum supported by morphology and DNA. Morphotypes 4, 5, and 6 belong to the same taxon on the basis of morphology of the hooklets only. For an accurate morphological diagnosis of the causative agent of gnathostomiasis, it is necessary to develop similar studies with other species of the genus.

Animals↗

PubMed2001

Measurement of left ventricular volumes by 3-dimensional echocardiography with tissue harmonic imaging: a comparison with magnetic resonance imaging.

We hypothesized that tissue harmonic imaging (THI) in comparison with fundamental imaging (FI) would improve endocardial border detection, and therefore in combination with 3-dimensional echocardiography (3D echo), it would be a precise method for left ventricular (LV) volume measurement. Ten healthy subjects and 18 consecutive patients with dilated hearts underwent estimation of LV volumes by magnetic resonance imaging (MRI) and transthoracic 3D echo with THI and FI. In patients, the agreement between MRI and 3D echo was closer with THI in comparison with FI for assessment of LV volumes. Thus the mean +/- 2 SD of differences between MRI and 3D echo with THI versus FI, respectively, was -6.4 +/- 40.0 mL versus -17.4 +/- 57.6 mL (P <.01) for the end-diastolic volume (EDV), and 0.0 +/- 26.6 mL versus -8.1 +/- 35.6 mL (P <.01) for the end-systolic volume (ESV). In patients, THI in comparison with FI approximately halved observer variation on EDV and ESV. In healthy subjects, only ESV showed significantly reduced observer variation by THI. In conclusion, because THI demonstrated a clinically relevant reduction in observer variation and a closer agreement to the MRI technique in patients with dilated hearts, it should replace FI in LV volume measurements.

Adult↗

PubMed1985

Inability of caliper measurement to enhance observer agreement in the interpretation of coronary cineangiograms.

Important clinical decisions are made on the basis of the interpretation of the degree of stenosis in the coronary cineangiogram. Thus, minimization of observer variation (both intra and inter) is crucial. The purpose of this investigation was to determine if measurement of stenotic lesions by caliper (CM) as compared with the usual eyeball method (EM) would reduce observer variation. Five observers, using the AHA scoring system, estimated maximal luminal narrowing in 14 segments on 10 films providing 2 reports on each film by EM and 2 by CM, thus making observations on 2800 segments. This allowed analysis of intraobserver variation for each reporter for method EM and CM, and for interobserver variation by each method. Since chance agreement is an important component in an observational study, a correction for this was made using the Kappa statistic. The results revealed that the mean Kappa by EM was 0.71 compared to 0.63 by CM (1 being perfect agreement and 0 no agreement). Agreement was much greater in proximal rather than distal segments. Interobserver agreement was consistently higher by EM K = 0.62 than CM K = 0.53 (p = 0.0007). A delineation of the types of disagreement and their clinical significance are important considerations in the evaluation of observer variation. It is concluded that the use of a caliper does not enhance either intra or interobserver agreement.

Cineangiography↗

PubMed1994

Reliability of intraocular pressure measurement with the Goldmann applanation tonometer in epidemiological studies.

The reproducibility of intraocular pressure (IOP) measurement with the Goldmann applanation tonometer was investigated as part of a population-based epidemiological study. Sixty-two subjects were examined in a first measurement session. The IOP was measured three times consecutively in both eyes according to a fixed protocol. The mean standard deviation (SD) of these measurements was 0.8 mmHg. The mean intraobserver variation for the first measurement was 1.64 (SD 2.07) mmHg. For the median of the three measurements the intra-observer variation was 1.50 (SD 1.96) mmHg. The mean inter-observer values were 1.79 (SD 2.41) mmHg for the first measurement and 1.60 (SD 2.15) mmHg for the median measurement. The correlation coefficient between the median values of the three measurements of both observers was 0.81. No systematic differences were found between the two observers. Using the median value of three consecutive measurements reduced the inter-observer variation by 11% and the intra-observer variation by 9% compared with a single measurement.

Aged↗

PubMed1997

Bone histomorphometry using interactive image analysis. A methodological study with application on the human temporomandibular joint.

The aim was to develop a reproducible method for bone histomorphometry with the aid of a computerized image analysis program, and to examine the variation when assessing the total and the trabecular bone volume. Histologic sections of 18 temporomandibular joint autopsy specimens were read interactively using a cursor. The two parameters total bone volume and trabecular bone volume, of the condyle and the temporal component respectively, were estimated 2 x by 1 observer using 3 different threshold settings: an automatic, a semi-automatic and a manual technique. The threshold was based on the gray-scale distribution of the image. 2 observers read the same sections with the aid of the semi-automatic technique. The intra-observer variation expressed as coefficient of variation ranged between 1.9% and 7.1% for the different parameters, when the automatic threshold setting technique was employed, and between 2.8% and 8.7% with the semi-automatic technique. The manual technique resulted in a high intra-observer variation with a coefficient of variation between 5.2% and 19.9%. There was a systematic difference between the estimates of the 2 observers. In general, intra- and inter-observer variation was higher in the temporal component than in the condyle. The inter-section variation was moderate, the coefficient of variation ranging from 3.8% to 11.1%. The automatic and semi-automatic techniques resulted in comparable intra-observer variation, with a lower bias in the estimates of the semi-automatic technique. By letting one observer apply the semi-automatic technique, it was possible to achieve fast and reproducible analysis of the total and trabecular bone volume.

Aged↗

PubMed2004

Reproducibility of intra-operative measurement of the mechanical axes of the lower limb during total knee replacement with a non-image-based navigation system.

OBJECTIVE: The restoration of a normal mechanical axis of the lower limb following total knee prosthesis (TKP) depends on the accuracy of the intra-operative measurement of the femoro-tibial angle. We have studied the reproducibility of intra-operative measurement of the coronal mechanical femoro-tibial axis with the OrthoPilot (Aesculap, Tuttlingen, Germany) non-image-based navigation system. MATERIAL AND METHODS: A consecutive series of 20 TKP (Aesculap SEARCH Evolution prosthesis) implanted by the same surgical team of two senior orthopedic surgeons was analyzed. They used a non-image-based navigation system that allows the mechanical axes of the femur and tibia to be defined with a kinematic analysis. The operating surgeon and assistant surgeon performed the kinematic analysis twice and once, respectively, and measured coronal mechanical femoro-tibial angles in maximal extension and at 90 degrees flexion without varus or valgus stress. RESULTS: The mean intra-observer variation in the measurement of the coronal mechanical femoro-tibial angle in maximal extension was 0.1 degrees (SD = 0.7 degrees). The mean intra-observer variation in the measurement of the coronal mechanical femoro-tibial angle at 90 degrees of knee flexion was 0.2 degrees (SD = 0.6 degrees). The mean inter-observer variation in the measurement of the coronal mechanical femoro-tibial angle in maximal extension was 0.1 degrees (SD = 0.7 degrees). The mean inter-observer variation in the measurement of the coronal mechanical femoro-tibial angle in maximal extension was 0.0 degrees (SD = 0.6 degrees). There were no significant differences and a high correlation between all paired intra- and inter-observer measurements. CONCLUSION: This system allows high reproducibility of the intra-operative measurement of the mechanical axes of the lower limb by a non-image-based kinematic registration of the hip, knee and ankle centers.

Arthroplasty, Replacement, Knee↗

PubMed2005

Variability of nuchal translucency measurement: a multicenter study in Thailand.

OBJECTIVES: To evaluate intra- and inter-observer variations of nuchal translucency (NT) measurements and study the duration of measurements. SUBJECTS: One hundred and forty-seven singleton pregnant women with 10-14 weeks of gestation who had attended antenatal clinic during January 1st, 2000-August 31st, 2001 were included. METHODS: Crown-rump length and NT were measured three times for each woman. Then, another examiner who was unaware of the previous results did the other three measurements. The duration of measurements was recorded. Intra-observer and inter-observer variations were analyzed by repeated ANOVA and paired t test, respectively. The correlation of NT measurements within each observer and between paired observers was evaluated by intraclass correlation coefficients (ICC). Kappa statistic was calculated for agreement. RESULTS: Intra-observer variation of all 10 examiners at three institutes was varied from 0.20 +/- 0.27 to 0.33 +/- 0.41 mm. Inter-observer variation at Chiang Mai University was 0.40 +/- 0.37 mm which was the highest value compared with those at Prince of Songkla and Khon Kaen University (p < 0.05). The mean duration of measurements was in range of 8-12 min. The intra-observer repeatability of the first two measurements showed ICCs varying from 0.61 to 0.94. The inter-observer repeatability of paired examiners showed a variation in ICC from 0.28-0.90. The kappa value expressing the intra- and inter-observer repeatability as being >95th or < or = 95th percentile was 0.73 and 0.72, respectively. CONCLUSIONS: NT measurement was reproducible for small variation and good agreement. The duration of measurements was acceptable.

Down Syndrome↗

PubMed1993

Analysis of embryonic development with a model for under- or overdispersion relative to binomial variation.

Observations from a study of the development of ovulations into embryos for Texel sheep are analysed with a model for count data that are under- or overdispersed relative to binomial variation. The analysis is based on maximum quasi-likelihood (McCullagh and Nelder, 1989, Generalized Linear Models, 2nd edition, London: Chapman and Hall), following an approach suggested by Williams (1982, Applied Statistics 31, 144-148). The dispersion parameter is developed as a combination of a variance component representing shared maternal effects and a correlation, typically negative, between ovulations within ewes. The number of ovulations (the binomial denominator) is included as an explanatory variable.

Androstenedione↗

PubMed2003

Partitioning interannual variability in net ecosystem exchange between climatic variability and functional change.

Interannual variability (IAV) in net ecosystem exchange of carbon (NEE) is a critical factor in projections of future ecosystem changes. However, our understanding of IAV is limited because of the difficulty in isolating its numerous causes. We proposed that IAV in NEE is primarily caused by climatic variability, through its direct effects on photosynthesis and respiration and through its indirect effects on carbon fluxes (i.e., the parameters that govern photosynthesis and respiration), hereafter called functional change. We employed a homogeneity-of-slopes model to identify the functional change contributing to IAV in NEE and nighttime ecosystem respiration (RE). The model uses multiple regression analysis to relate NEE and RE with climatic variables for individual years and for all years. If the use of different slopes for each year significantly improves the model fitting compared to the use of one slope for all years, we consider that functional change exists, at least on annual time scales. With the functional change detected, we then partition the observed variation in NEE or RE to four components, namely, the functional change, the direct effect of interannual climatic variability, the direct effect of seasonal climatic variation, and random error. Application of this approach to a data set collected at the Duke Forest AmeriFlux site from August 1997 to December 2001 indicated that functional change, interannual climatic variability, seasonal climatic variation and random error explained 9.9, 8.9, 59.9 and 21.3%, respectively, of the observed variation in NEE and 13.1, 5.0, 38.1 and 43.8%, respectively, of the observed variation in RE.

Carbon Dioxide↗

PubMed2002

The evaluation of a new digital semi-automated system for the radiological assessment of distal radial fractures.

OBJECTIVE: To compare intra- and inter-observer variation for measurements of wrist deformity using a manual method of measurement and a semi-automated digital system developed in our department. DESIGN: Four observers measured radial angle, radial shift, radial length, palmar tilt, and dorsal shift on ten wrist-fracture films using a standardised protocol. Each observer made measurements directly from the radiograph on three occasions, and on a further three occasions digitised images were viewed and measurements made with semi-automated on-screen measurement tools. RESULTS: Manual measurements took 12 min per case compared with 3 min for the digital system. The digital system resulted in improved intra-observer variation for all measurements and an improvement in inter-observer variation for all measurements except posterior tilt. CONCLUSION: The new system allows greater precision in assessing fracture reduction and follow-up. Its principal application is in studies that utilise the wrist as a model for fracture healing.

Humans↗

PubMed1996

Transvaginal ultrasonographic measurements of endometrial thickness: a reproducibility study.

OBJECTIVE: The study was undertaken to assess the reproducibility of endometrial thickness measurements by transvaginal ultrasonography (TVS). METHODS: In a prospective blind study, two examiners measured the endometrial thickness of 25 patients by TVS on two separate occasions 30 minutes apart. RESULTS: The reliability test performed for each examiner was statistically less significant for the intra-observer variation of each observer (r = 0.95 and r = 0.93), than between both examiners (r = 0.85). Although there was no statistically significant difference between the observations, the mean range of observations was 2.12 + 1.27 mm. CONCLUSIONS: A safety margin of error should be taken into consideration while recommending a cutoff under which no curettage is needed.

Adult↗

PubMed1983

The response of male broiler chickens to diets with various protein and energy contents during the growing phase.

1. In two trials each using 2 400 male broilers, the regression of body weight on the linear effects of dietary protein, energy and age, the quadratic effect of age, and their interactions, accounted for approximately 99% of the observed variation during the growing and finishing period (3 to 8 weeks of age). Increasing either dietary protein or energy content significantly increased body weight. 2. The regression of food consumption on the linear effects of age, protein, energy and protein X energy interaction, and the quadratic effect of age accounted for 94% of the observed variation. The regression of food utilisation on the linear effects of protein, energy, and age and the quadratic effects of dietary protein and age accounted for 97% of the observed variation. Food consumption and efficiency were dependent on both dietary protein and energy, increasing with increases in either dietary protein or energy content. 3. The regression of fat in the dressed carcass on the linear effects of protein, energy and age accounted for 19% of the observed variation. Carcass fat increased with increasing age and dietary energy, and decreased with increasing dietary protein. 4. Although body weight, food consumption and utilisation were significantly different between trials, the proportion of carcass fat was not.

Aging↗

PubMed2006

Sequence analysis of the msp4 gene of Anaplasma ovis strains.

Anaplasma ovis (Rickettsiales: Anaplasmataceae) is a tick-borne pathogen of sheep, goats and wild ruminants. The genetic diversity of A. ovis strains has not been well characterized due to the lack of sequence information. In this study, we evaluated bighorn sheep (Ovis canadensis) and mule deer (Odocoileus hemionus) from Montana for infection with A. ovis by serology and sequence analysis of the msp4 gene. Antibodies to Anaplasma spp. were detected in 37% and 39% of bighorn sheep and mule deer analyzed, respectively. Four new msp4 genotypes were identified. The A. ovismsp4 sequences identified herein were analyzed together with sequences reported previously for the characterization of the genetic diversity of A. ovis strains in comparison with other Anaplasma spp. The results of these studies demonstrated that although A. ovismsp4 genotypes may vary among geographic regions and between sheep and deer hosts, the variation observed was less than the variation observed between A. marginale and A. phagocytophilum strains. The results reported herein further confirm that A. ovis infection occurs in natural wild ruminant populations in Western United States and that bighorn sheep and mule deer may serve as wildlife reservoirs of A. ovis.

Anaplasma ovis↗

PubMed1997

Radiology's Achilles' heel: error and variation in the interpretation of the Röntgen image.

The performance of the human eye and brain has failed to keep pace with the enormous technical progress in the first full century of radiology. Errors and variations in interpretation now represent the weakest aspect of clinical imaging. Those interpretations which differ from the consensus view of a panel of "experts" may be regarded as errors; where experts fail to achieve consensus, differing reports are regarded as "observer variation". Errors arise from poor technique, failures of perception, lack of knowledge and misjudgments. Observer variation is substantial and should be taken into account when different diagnostic methods are compared; in many cases the difference between observers outweighs the difference between techniques. Strategies for reducing error include attention to viewing conditions, training of the observers, availability of previous films and relevant clinical data, dual or multiple reporting, standardization of terminology and report format, and assistance from computers. Digital acquisition and display will probably not affect observer variation but the performance of radiologists, as measured by receiver operating characteristic (ROC) analysis, may be improved by computer-directed search for specific image features. Other current developments show that where image features can be comprehensively described, computer analysis can replace the perception function of the observer, whilst the function of interpretation can in some cases be performed better by artificial neural networks. However, computer-assisted diagnosis is still in its infancy and complete replacement of the human observer is as yet a remote possibility.

Diagnostic Errors↗

PubMed2000

Somatostatin-receptor scintigraphy in Graves' disease: reproducibility and variance of orbital activity.

Somatostatin-receptor (SSTR) scintigraphy using the single photon emission computed tomography (SPECT) technique allows the assessment of orbital inflammation in patients with Graves' disease. Previous studies showed differences in orbital octreotide uptake already 4 hr after injection. In this study, analysis of inter-/intra-observer variance and reproducibility in the evaluation of orbital SPECT images was performed. First, SPECT data of one representative female patient with clinically active Graves' ophthalmopathy (GO), obtained 4 hr after intravenous injection of 110 MBq 111In-pentetreotide and processed by filtered backprojection, were analyzed. Transverse SPECT images were reconstructed, an optimal orbital image was selected and predetermined regions of interests (ROIs) for both orbits were positioned by three independent observers 15 to 19 times each. In a second step, SPECT data of 8 different patients with GO were evaluated in the same manner by four independent observers 3 to 4 times each. Variance component partitioning was used to compare the order of intra- and inter-observer variation. For the right and the left orbit, the inter-observer variance proportion was 90% and 79%, whereas intra-observer variance partition was 10% and 21%, respectively. The corresponding ratios 0.11 and 0.27 summarize the comparison of sources of variance. The overall reliability was 84%, representing the patients influence on the total variance. Intra-observer reliability for both orbits was 88%, 89%, 97% and 98% (mean over orbits), respectively for observers I to IV. Using the Spearman Brown prophecy formula it follows that two replications per patient are sufficient to ensure a minimum reproducibility of 90%, which is also confirmed by the low intra-observer variation. Furthermore, intra-class correlation as a measure of (multiple) observer reproducibility was 94%. In conclusion, due to the increased inter-observer variance proportion and the high variation in intra-observer reliability, evaluations of orbital SSTR scintigraphy have to be done by the same and experienced observer leading to comparable data. But an automatic and quantitative computerized technique for evaluation of these SPECT data should be exactly reproducible and probably lead to more accurate and representative results.

Adult↗