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Results for “Reproducibility”

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PubMed2003

Interobserver reproducibility of MIB-1 labeling index in astrocytic tumors using different counting methods.

MIB-1 labeling index has been used as a complementary method to differentiate better and worse prognostic groups of astrocytic tumors. However, its reproducibility has been doubted because of the interlaboratory and interobserver variability. We studied the interobserver reproducibility of four manual counting methods of MIB-1 labeling index, including direct counting, area fraction, line intersection with a graticule, and line intersection without a graticule to estimate the total number of the cells. Using line intersection estimate, either with or without a graticule, yielded a worse result. Those MIB-1 labeling indices of astrocytomas were overlapping with those of anaplastic astrocytomas and glioblastomas. Besides, the intraclass correlation coefficient was smaller, and the coefficient of variation was greater than that attained when using a graticule and counting the total number of cells either directly or by area-fraction estimate. The level of interobserver agreement using an MIB-1 labeling index cutoff value of 11.0 was moderate to substantial when applying the line-intersection estimate, and it was almost perfect when applying the direct counting or the area-fraction estimate. The interobserver reproducibility and agreement of MIB-1 labeling index in astrocytic tumors were different depending on the counting methods. Direct counting with a graticule yielded the best result. Before establishing reference standards for staining and counting, the reproducibility of MIB-1 labeling index should be verified.

Adolescent↗

PubMed2006

From sample similarity to ensemble similarity: probabilistic distance measures in reproducing kernel Hilbert space.

This paper addresses the problem of characterizing ensemble similarity from sample similarity in a principled manner. Using reproducing kernel as a characterization of sample similarity, we suggest a probabilistic distance measure in the reproducing kernel Hilbert space (RKHS) as the ensemble similarity. Assuming normality in the RKHS, we derive analytic expressions for probabilistic distance measures that are commonly used in many applications, such as Chernoff distance (or the Bhattacharyya distance as its special case), Kullback-Leibler divergence, etc. Since the reproducing kernel implicitly embeds a nonlinear mapping, our approach presents a new way to study these distances whose feasibility and efficiency is demonstrated using experiments with synthetic and real examples. Further, we extend the ensemble similarity to the reproducing kernel for ensemble and study the ensemble similarity for more general data representations.

Algorithms↗

PubMed1993

An assessment of the reproducibility of combined glottography in a clinical setting.

Although combined glottography has potential as a clinical tool, it has had limited use in the monitoring of laryngeal function before and after treatment. There is no data about the standardization nor reproducibility of the procedure. An indication of the reproducibility of combined glottography is paramount if changes in laryngeal function are to be measured accurately. Using a standardized technique, two complimentary studies examined the reproducibility of combined glottography within one sitting (Study 1) and over time (Study 2). The components of variance were analysed (ANOVA). In Study 1 the variance under controlled conditions for Open Quotient (OQ) and Speed Quotient (SQ) was only 13% and 18% respectively of the total, whilst in Study 2 the variance over time for OQ and SQ was 55% and 58% respectively. Under controlled conditions combined glottography is a reproducible technique.

Adult↗

PubMed1989

Reproducibility of 24-hour non-invasive ambulatory blood pressure monitoring using the Suntech Accutracker.

1. The reproducibility of 24-hour non-invasive ambulatory blood pressure monitoring (ABPM) using the 'Accutracker' (AC) (Suntech Medical Instruments, NC) was determined to evaluate the AC's suitability for clinical trials investigating the effects of environmental determinants on blood pressure. 2. Six healthy males from the University Department of Medicine underwent 24 h ABPM on the same working day of the week on six occasions. Reproducibility of hourly mean systolic blood pressure (SBP) and diastolic blood pressure (DBP) was determined using analysis of variance. 3. No familiarization effect of measurement with the AC was detected. 4. When comparing four time periods (0000-0759 h, 0800-1259 h, 1300-1859 h and 1900-2359 h), reproducibility of SBP was highest during the afternoon (1300-1859 h) whereas reproducibility of DBP was highest during late morning (0800-1259 h). 5. Hourly mean SBP was significantly lower during late morning (0800-1259 h) than in the afternoon (1300-1859 h) or at night (1900-2359 h). Hourly mean SBP and DBP was significantly lower during sleep. 6. Based on a select sample of volunteers, the AC is suitable for clinical trials involving paired measurements, particularly between 0800 and 1900 h when only 10-15 subjects would provide 80% power to demonstrate a 5 mmHg difference in SBP and DBP significant at the 0.05 level.

Adolescent↗

PubMed1996

The mechanisms responsible for lack of reproducible induction of atrioventricular nodal reentrant tachycardia.

INTRODUCTION: AV nodal reentrant tachycardia (AVNRT) is not always reproducibly inducible. The purpose of this study was to determine the mechanisms responsible for the lack of reproducible induction of AVNRT. METHODS AND RESULTS: The induction of AVNRT was assessed with atrial burst pacing, and with atrial and ventricular programmed stimulation, each with one and two extrastimuli, in 103 patients with AVNRT. The stimulation protocol was repeated 10 times in the baseline state, during isoproterenol infusion, and after atropine administration, or until AVNRT was induced in 7 of 10 attempts. The mechanisms responsible for < 7 of 10 inductions were classified as: (1) the inability to achieve critical AH prolongation; (2) fast pathway block; and (3) slow pathway block. The induction endpoint was achieved in 90 patients: 55 in the baseline state, 34 during isoproterenol infusion, and 1 after atropine. The mechanism of noninducibility in the baseline state (n = 48) was the inability to achieve a critical AH interval in 20%, fast pathway block in 49%, and slow pathway block in 31% (P = 0.02). During isoproterenol administration (n = 14) and after atropine administration (n = 13), the three mechanisms were equally responsible for nonreproducible induction of AVNRT. CONCLUSIONS: The induction of AVNRT is poorly reproducible in approximately 10% of patients. In the baseline state, the most common reason for the inability to reproducibly induce AVNRT is fast pathway block. In the presence of isoproterenol or atropine, each of the three mechanisms was equally responsible for noninducibility of AVNRT.

Adrenergic beta-Agonists↗

PubMed1984

Reproducibility of probing attachment level measurements.

The reproducibility of probing attachment level measurements in incisors, cuspids and premolars was studied in 2 groups of patients with severely advanced periodontal disease. The results showed that approximately 90% of the recordings could be reproduced within within +/- 1.0 mm difference. This was found for intra-examiner as well as inter-examiner comparisons of 2 examiners. Measurements using onlay margins for reference point demonstrated somewhat less variability than the use of cemento-enamel junction for reference. The level of reproducibility varied notably between patients and was improved following non-surgical periodontal therapy. Also, the reproducibility varied significantly between tooth types, tooth surfaces and probing pocket depths. It was concluded that in clinical studies, the evaluation of the healing response of individual lesions should include consideration of the variability of repeated measurements for each of the investigated tooth sites.

Bicuspid↗

PubMed1989

The effect of in-vivo-occurring errors in the reproducibility of radiographs on the use of the subtraction technique.

A device for serial radiography in maxillary and mandibular premolar and molar regions was developed. Radiographs of 9 patients were made during a period of 1 year. When testing the device, the influence of the time interval between the radiographs and the influence of the construction of the device on the reproducibility of the X-ray images were determined. An increase of the time interval between radiographs reduced the reproducibility. The use of bilateral bite blocks improved the reproducibility of the X-ray images in comparison with the images obtained with a device with a one-sided bite block. Errors in the reproducibility caused differences in the image geometry of radiographs. The in-vivo-found differences were studied for their effect on the detection threshold of observers using photographic subtraction radiography. An increase of the differences in image geometry between the radiographs resulted in a higher detection threshold and a higher % of false positive decisions. It appeared that very small differences between clinical radiographs, corresponding with an angulation error of 0.7 degrees, can be tolerated in order to prevent the occurrence of high numbers of type-I errors. The % of radiographs, which met this requirement and could be used for photographic subtraction radiography, was 55%, when taken at time intervals of 1 year.

Adult↗

PubMed1989

Reproducibility and overlapping of bitewing radiographs: comparison of Eggen-bite with Kwik-bite.

In the present study the reproducibility of horizontal dimensions and of overlappings of two filmholder techniques with aiming devices (Eggen-bite and Kwik-bite) and additionally the number of overlappings on the resulting bitewing radiographs were compared. The overlapping reproducibility was significantly higher with Kwik-bite. The microdensitometric reproducibility demonstrated the same tendency, but the result was not significant. Bitewings carried out by an oral radiologist demonstrated fewer overlappings with Eggen-bite than with Kwik-bite, while bitewings carried out by inexperienced students revealed no difference between the methods. Both reproducibility and number of overlappings should be taken into consideration when bitewing filmholder techniques are used in epidemiological and longitudinal studies.

Densitometry↗

PubMed1989

Histological and cytological fine needle biopsies from focal liver lesions. Intra- and interobserver reproducibility of diagnoses.

In 175 consecutive cases of ultrasonically detected focal liver lesions both cytological (CFNB) and histological (HFNB) fine needle biopsies were performed with two different 0.6 mm needles and evaluated twice and blindly by two examiners. The intra- and interobserver kappa values for reproducibility concerning a malignant diagnosis were higher for CFNB (0.94-0.96) than for HFNB (0.89-0.93). At re-evaluation most inconsistent diagnoses could be related to biopsies of poor quality (CFNB 4 cases, HFNB 13 cases). In three cases (CFNB 2, HFNB 1) false interpretation of the biopsies could have been the cause of inconsistent diagnoses. CFNB resulted in significantly more consistent, malignant diagnoses than HFNB, and CFNB is therefore recommended as the method of choice in cases of a known primary tumour. A morphological diagnosis of a breast carcinoma and of a colonic carcinoma as the primary tumour was better reproduced by HFNB than by CFNB. A diagnosis of a primary liver tumour and of a small cell carcinoma of the lung had a reasonable reproducibility with both methods (kappas greater than 0.60). Other diagnoses were poorly reproduced or occurred infrequently. Both methods are recommended for use in cases of an unknown primary tumour.

Biopsy, Needle↗

PubMed1982

Reproducible and rapid methods for the isolation and assay of a-factor, a yeast mating hormone.

The Saccharomyces cerevisiae mating hormone a-factor has been difficult to isolate reproducibly in sufficient yields by methods using ion-exchange chromatography, probably because of its pronounced hydrophobicity. In this work, a hydrophobic adsorbent (Amberlite XAD-2), in an insoluble bead from, was used to isolate larger (up to sixfold greater than previous reports) and quite reproducible (12% standard deviation) quantities of a-factor by adsorption from cell-free filtrates of a cultures. Moreover, when the beads were added to the cultures at the time of inoculation, sixfold greater yields were obtained than when a-factor was adsorbed to the beads from cell-free filtrates. a-Factor was readily eluted from the beads with 1-propanol. The same adsorbent could also be used in the partial purification of the less hydrophobic alpha-factor. Adsorption of both hormones by Amberlite XAD-2 gave a degree of purification comparable to that obtained by the first steps of previously published methods while providing larger yields of hormones. The present procedure is shorter, simpler, and, for a-factor, more reproducible. The activities of both hormones were quantitated by using an assay in which the size distribution of cells in the population was monitored after the addition of hormone of the opposite mating type. The extent of increase in cell size which accompanies hormone treatment is a function of the hormone concentration. To ensure solubilization of a-factor in the aqueous bioassay system, samples were diluted into bovine serum albumin solutions and sonicated before assaying. The resulting assay is most sensitive at hormone concentrations between 0.05 and 2 U/ml, can reliably detect as little as 0.16 ng of hormone, gave results reproducible within 16%, and is convenient for a large number (>100) of samples.

Adsorption↗

PubMed1994

Reproducibility of the vascular response to heating in human skin.

Blood flow in human skin increases enormously in response to direct heating. If local skin temperature is held above 42 degrees C, blood flow eventually stabilizes at a level beyond which other influences, barring change in blood pressure, can produce no further increase. If this maximal level is a reproducible characteristic of an individual's cutaneous vasculature, it could be useful in comparing individuals; for example, in their response to hyperthermia. Our experiments were carried out to discover whether the maximal response of the vasculature of the skin of the forearm can be reproduced within reasonable limits and, also, to clarify the time course of the response. We used water sprayed over the surface of the forearms of 10 subjects to hold skin temperature above 42 degrees C for 60 min. During the last 10 min of heating, forearm blood flow (via venous occlusion plethysmography) was stable, at a level ranging from 16 to 38 ml.min-1.100 ml-1. This level, normalized to a blood pressure of 100 mmHg, was reproduced in a given individual on four or five occasions, with an average coefficient of variation of 10%. The response was 77 +/- 11% (SD) complete after 20 min of heating. Elapsed time at 90% of the final value was 35 +/- 9 (SD) min. We conclude that the maximal forearm blood flow response to local heating is a reproducible characteristic of the cutaneous vasculature with potential utility in the scaling of responses between and within individuals.

Adult↗

PubMed2004

Dynamics and reproducibility of a moderately complex sensory-motor response in the medicinal leech.

Local bending, a motor response caused by mechanical stimulation of the leech skin, has been shown to be remarkably reproducible, in its initial phase, despite the highly variable firing of motoneurons sustaining it. In this work, the reproducibility of local bending was further analyzed by monitoring it over a longer period of time and by using more intact preparations, in which muscle activation in an entire body segment was studied. Our experiments showed that local bending is a moderately complex motor response, composed of a sequence of four different phases, which were consistently identified in all leeches. During each phase, longitudinal and circular muscles in specific areas of the body segment acted synergistically, being co-activated or co-inhibited depending on their position relative to the stimulation site. Onset and duration of the first phase were reproducible across different trials and different animals as a result of the massive co-activation of excitatory motoneurons sustaining it. The other phases were produced by the inhibition of excitatory and activation of inhibitory motoneurons, and also by the intrinsic relaxation dynamics of leech muscles. As a consequence, their duration and relative timing was variable across different preparations, whereas their order of appearance was conserved. These results suggest that, during local bending, the leech neuromuscular system 1) operates a reduction of its available degrees of freedom, by simultaneously recruiting groups of otherwise antagonistic muscles and large populations of motoneurons; and 2) ensures reliability and effectiveness of this escape reflex, by guaranteeing the reproducibility of its crucial initial phase.

Animals↗

PubMed2002

Reconstructed skin kits: reproducibility of cutaneous irritancy testing.

The aim of this study was to determine the reproducibility of data obtained from in vitro irritation testing using three industrial reconstructed human epidermis models, EpiDerm, Episkin and SkinEthic, and one in-house model developed at Wella/Cosmital. A common protocol was established based on the measurement of cytotoxicity in the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay and of extracellular release of proinflammatory mediators and cytosolic enzymes after a range of exposure times to sodium lauryl sulfate (SLS). This time course protocol was applied to 6 different batches of each skin model using triplicate tissue cultures per test condition. The parameters analyzed for intra- and inter-batch reproducibility were the cell viability determined as MTT reduction capacity and the ET-50 values in the 6 batches, as well as the release of the cytokine IL-1alpha and of the cellular enzymes LDH and GOT in 3 batches only. The MTT viability results showed that EpiDerm was the most resistant to the SLS treatment and at the same time the most reproducible model, SkinEthic was the most sensitive to SLS and the least reproducible, and Episkin and the Cosmital model were intermediate. Measurements of IL-1alpha release showed a relatively high intra- and inter-batch variability in all the skin models. It was not possible to detect the extracellular release of the enzymes LDH and GOT in the Episkin assay medium. With the 3 other models, the release of LDH and GOT varied in about the same range as that of IL-1alpha. For all the parameters in this study, the inter-batch variability was generally greater than the intra-batch variability. A possible reduction in the number of batches and replicates for future applications in routine irritancy testing is discussed on the basis of the results obtained using 6 batches in triplicate.

Humans↗

PubMed1987

Reproducibility of echocardiographic left ventricular measurements.

Serial echocardiograms with acceptable reproducibility of measurements may be produced by careful performance and interpretation of the studies. The following recommendations have been shown to enhance reproducibility. Strict adherence to quality control is necessary to generate echocardiograms of the highest technical quality. Sonographers should be aware of the definition of a technically adequate study--including correct beam or plane angulation and continuous visualization of interfaces--and seek this ideal in every study. Participation by the sonographer in performance of measurements enhances recognition of the requirements for accurate quantitative echocardiography. Regular machine calibration is a prerequisite to accurate quantitative echocardiography. Considerable effort must be made to standardize the position of each acoustic window and angulation from which the patient is imaged--with deviation from these norms being recorded for future reference. If at all possible, measurements should be taken at end expiration. If that is not possible, measurement of several consecutive beats will limit the impact of respiratory variation. A uniform convention of measurement should be adopted. The best candidates for M-mode measurements are the American Society of Echocardiography recommendations for general measurement and the Penn convention for calculation of M-mode left ventricular mass. Further data is needed to determine which approaches to two-dimensional measurements best combine accuracy and reproducibility. Interpretation of echocardiograms may be made most reproducible by measuring pertinent parameters from multiple beats and using the mean as the result and by having at least two readers interpret each echocardiogram, possibly with two separate readings by each reader.

Cardiac Volume↗

PubMed1985

Reproducibility of computer-aided image-analysis-derived estimates of the depth and area of radiolucencies in approximal enamel.

In vivo studies of caries progression from serial bite-wing radiographs require the reproducible detection and measurement of approximal radiolucencies in enamel; the aim of this study was to evaluate the reproducibility of a new computer-aided image analysis method. Three series of radiographs depicting natural caries lesions were employed: films of 11-12-year-old (Hounslow) schoolchildren, dental students from Hong Kong (HKDS), and extracted Hong Kong teeth (EXT). Each surface was "searched" three times, resulting in data from 450, 600, and 180 searches, respectively. Lesion detection was consistent for all but two of the 1230 searches. Average values for the standard error of the mean (SEM) of triple determinations of depth % were between 2.0 and 3.5%, while the mean SEM for area was from 0.03 to 0.04 mm2. Average test/re-test correlations ranged from 0.963 to 0.871 for depth and from 0.963 to 0.884 for area, while average reliability coefficients ranged from 0.937 to 0.821 for depth and 0.963 to 0.886 for area. There was a significant difference (P less than 0.001) between the reproducibility of the two clinical series, with measurements of the Hounslow lesions being more consistent. When compared with the reproducibility of attempts to grade radiolucency size visually, the image analysis method appears to offer considerable advantages, in that consistent estimates of radiolucency size are now possible. This method may facilitate more sensitive assessments of the behavior of lesions over time than has hitherto been possible.

Adult↗

PubMed1983

Reproducibility and observer variation at computed tomography and ultrasound of the normal pancreas.

In order to evaluate the reproducibility of computed tomography (CT) and ultrasound (US), 13 patients with a normal pancreas were examined twice with the two techniques by the same observers. The results of the measurements of the pancreas were reproducible using both CT and US. In estimating the intraobserver variation at CT in 20 patients, the location and spread of the measurements of the diameters of the pancreatic head were reproducible, but the diameters of the pancreatic body and tail were significantly larger at the second observation. Further, the differences in the measurements of the size and dispersion of the pancreatic diameters at CT between two observers were significant, apart from the diameter of the pancreatic tail, where no significant difference was noted. The differences between two observers were greater than for the same. Using US, the results may indicate that the measurements were even less reproducible than using CT, both for the same observer and between two observers. However, all the measured diameters within the 95 per cent confidence intervals, were within the normal range. Consequently, even if most measurements differed significantly, these differences may probably not lead to any false conclusions concerning the limits of the normal size of the pancreas.

Diagnostic Errors↗

PubMed2005

Reproducible clusters from microarray research: whither?

MOTIVATION: In cluster analysis, the validity of specific solutions, algorithms, and procedures present significant challenges because there is no null hypothesis to test and no 'right answer'. It has been noted that a replicable classification is not necessarily a useful one, but a useful one that characterizes some aspect of the population must be replicable. By replicable we mean reproducible across multiple samplings from the same population. Methodologists have suggested that the validity of clustering methods should be based on classifications that yield reproducible findings beyond chance levels. We used this approach to determine the performance of commonly used clustering algorithms and the degree of replicability achieved using several microarray datasets. METHODS: We considered four commonly used iterative partitioning algorithms (Self Organizing Maps (SOM), K-means, Clutsering LARge Applications (CLARA), and Fuzzy C-means) and evaluated their performances on 37 microarray datasets, with sample sizes ranging from 12 to 172. We assessed reproducibility of the clustering algorithm by measuring the strength of relationship between clustering outputs of subsamples of 37 datasets. Cluster stability was quantified using Cramer's v2 from a kXk table. Cramer's v2 is equivalent to the squared canonical correlation coefficient between two sets of nominal variables. Potential scores range from 0 to 1, with 1 denoting perfect reproducibility. RESULTS: All four clustering routines show increased stability with larger sample sizes. K-means and SOM showed a gradual increase in stability with increasing sample size. CLARA and Fuzzy C-means, however, yielded low stability scores until sample sizes approached 30 and then gradually increased thereafter. Average stability never exceeded 0.55 for the four clustering routines, even at a sample size of 50. These findings suggest several plausible scenarios: (1) microarray datasets lack natural clustering structure thereby producing low stability scores on all four methods; (2) the algorithms studied do not produce reliable results and/or (3) sample sizes typically used in microarray research may be too small to support derivation of reliable clustering results. Further research should be directed towards evaluating stability performances of more clustering algorithms on more datasets specially having larger sample sizes with larger numbers of clusters considered.

Cluster Analysis↗

PubMed2004

Validity and reproducibility of an interviewer-administered food frequency questionnaire for healthy French-Canadian men and women.

OBJECTIVE: To evaluate the validity (study 1) and the reproducibility (study 2) of an interviewer-administered food frequency questionnaire (FFQ). METHOD: The FFQ was designed at Laval University and contains 91 items and 33 subquestions. STUDY 1: The FFQ was compared against a 3-day food record (2 week-days and 1 weekend-day), at week 0, 6 and 12 of a nutritional intervention. STUDY 2: In order to evaluate the reproducibility of the FFQ, 2 registered dietitians administered the FFQ 4-weeks apart among subjects who were not part of the nutritional intervention. RESULTS: STUDY 1: Mean values for intake of most nutrients assessed by the FFQ and by the 3-day food record were not statistically different. Energy-adjusted correlation coefficients for major macronutrients ranged from 0.36 for proteins to 0.60 for carbohydrates (p < or = 0.01). Agreement analysis revealed that on average, 35% of the subjects were classified in the same quartile when nutrients were assessed by either the 3-day food record or the FFQ. STUDY 2: Significant associations were observed between dietary measurements derived from the two FFQs administered 4 weeks apart. Correlation coefficients for the reproducibility of macronutrients ranged from 0.66 for carbohydrates to 0.83 for lipids after energy adjustment. On average, 46% of the subjects were classified in the same quartile when nutrient intakes were assessed by either FFQ. CONCLUSION: These data indicated that the FFQ developed has a good validity and is reproducible.

Journal Article↗