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Results for “Repeatability and Reproducibility”

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PubMed1994

Ca2+ mobilization by caffeine in single smooth muscle cells of the rat tail artery.

The fluorescent dye fura-2 was used to study the effects of caffeine on cytosolic free Ca2+ level ([Ca2+]i) in freshly isolated single cells from the rat tail artery. Caffeine caused a concentration-dependent transient increase in [Ca2+]i and shortening of the cell. At higher concentrations (> 2 mM), a tonic increase in [Ca2+]i was also observed. The caffeine-induced changes in [Ca2+]i were reproducible with repeated challenges, even though the cells had contracted due to previous exposure to caffeine. Removal of extracellular Ca2+ reduced the resting [Ca2+]i to about half and abolished the tonic Ca2+ increase to caffeine. The transient component was not significantly affected to the first caffeine challenge after Ca2+ removal, but was abolished to the second challenge. Ryanodine (10 microM) significantly inhibited the responses to caffeine while nifedipine and TMB-8-(8-(diethylamino)octyl ester of 3,4,5-trimethoxybenzoic acid) were not effective. Thapsigargin (10-100 microM) induced a sustained increase in [Ca2+]i to 67 nM. The response of caffeine was not affected by thapsigargin. Pretreatment of the cells with noradrenaline (10 microM) abolished subsequent response to caffeine. These results show that Ca2+ responses to caffeine in single cells from the rat tail artery are reproducible with repeated caffeine challenge. Therefore, single cells can be used for comparison studies of the effects of pharmacological agents.

Animals↗

PubMedDate not supplied

A modification of the staining technique of reticular fibres for image analysis of the cardiac collagen network.

INTRODUCTION: Silver stain of reticular fibres demonstrates the fine structure of the cardiac collagen network. However, nuclei are also stained with current techniques, a drawback that makes computer image analysis difficult. To solve this problem our study was designed to modify Gomori's method. Reactive concentrations and action times represent the core of that modification. Only stromal tissue is stained. The technique was tested for repeatability and reproducibility to assess the precision of the measurement procedure in the assessment of myocardial collagen in a consecutive series of myocardial samples from patients with and without heart muscle disease. In addition, we checked the reliability of the method by comparing our results with the point-counting method (PCM). METHODS: The right ventricular myocardium was fixed in 10% buffered formaldehyde and routinely processed. Paraffin sections (4 microm) were stained with several modifications of Gomori's method. Variable concentrations of potassium permanganate, silver solutions and different oxidation times were tried. A field from each sample was digitized. Additionally, the technique was tested for repeatability and reproducibility. RESULTS: We obtained absence of background and nuclear staining together with a highly contrasted image of the collagen network with 3 min oxidation with 2% potassium permanganate and a silver concentration of 1% during 5 min. In this way, it was very easy to perform acquisition, thresholding and area measurement without any further manual processing of the image. CONCLUSIONS: This technique appears very helpful for the quantitative study of the cardiac collagen network by means of computerized image analysis systems.

Adolescent↗

PubMed2004

Method for determination of methane potentials of solid organic waste.

A laboratory procedure is described for measuring methane potentials of organic solid waste. Triplicate reactors with 10 grams of volatile solids were incubated at 55 degrees C with 400 ml of inoculum from a thermophilic biogas plant and the methane production was followed over a 50-day period by regular measurements of methane on a gas chromatograph. The procedure involves blanks as well as cellulose controls. Methane potentials have been measured for source-separated organic household waste and for individual waste materials. The procedure has been evaluated regarding practicality, workload, detection limit, repeatability and reproducibility as well as quality control procedures. For the source-separated organic household waste a methane potential of 495 ml CH4/g VS was found. For fat and oil a lag-phase of several days was seen. The protein sample was clearly inhibited and the maximal methane potential was therefore not achieved. For paper bags, starch and glucose 63, 84 and 94% of the theoretical methane potential was achieved respectively. A detection limit of 72.5 ml CH4/g VS was calculated from the results. This is acceptable, since the methane potential of the tested waste materials was in the range of 200-500 ml CH4/g VS. The determination of methane potentials is a biological method subject to relatively large variation due to the use of non-standardized inoculum and waste heterogeneity. Therefore, procedures for addressing repeatability and reproducibility are suggested.

Bioreactors↗

PubMed1996

A collaborative study on the detection of staphylococcal enterotoxins in foods by an enzyme immunoassay kit (RIDASCREEN).

The RIDASCREEN SET kit (R-Biopharm GmbH, Darmstadt, Germany), a commercial staphylococcal enterotoxin (SE) immunoassay kit, utilizes monovalent capture antibodies against SE types A to E (SEA to SEE); therefore, it simultaneously detects and identifies the enterotoxin types. A collaborative study was conducted to ascertain whether the specificity, sensitivity, repeatability and reproducibility of the kits would meet food safety criteria. Twelve Canadian laboratories participated in this study to analyze various foods to which 1.0 to 2.0 ng of SE/g had been added and negative control samples. The results indicate that the sensitivity and specificity of the kit were excellent; all collaborators were able to detect the minimum toxin levels of 1.0 ng SEA/g in ham and cheese, 1.0 ng SEB/g in salami and turkey, and 2.0 ng SED/g in other samples without any false-negative results. With regard to negative control samples, all analysts obtained correct results except for one analyst who recorded weak false-positive results with several foods detecting SEC or SEA. The overall rate of false-positive results was 0.7% for 600 triplicate assays. In addition, it was confirmed that the RIDASCREEN kit did not yield false-positive results with mussels in contrast to some other EIA kits. Overall repeatability and reproducibility of the kit were in the range of 11.69-42.57% and 17.25-68.05%, respectively.

Animals↗

PubMed1996

Intrasubject variability of repeated pulmonary function measurements in preterm ventilated infants.

This study set out to describe the variability and assess the reproducibility of repeated pulmonary function measurements in ventilated preterm infants. We measured tidal volume (VT), lung compliance (CL), and resistance (RL) in 16 infants (mean +/- SD: birthweight 1222 +/- 343 g) during spontaneous breathing and during mechanical ventilation, suppressing breathing efforts by mild hyperventilation. CL and RL were calculated from the equation of motion using linear regression analysis (LR), and by the Mead and Wittenberger method (MW). Flow and transpulmonary pressure were recorded for at least two consecutive periods, after which the esophageal tube was removed and replaced 1 hour later for a second set of recordings. The mean percent change (% delta) between the initial and the repeated measurements with their respective 95% confidence intervals were calculated. Reproducibility was assessed by the intraclass correlation coefficient (ICC) (total agreement = 1, good reproducibility > or = 0.75). The mean % delta between initial and repeat measurements during spontaneous breathing ranged from 11% to 14% for CL and VT, and from 22% to 32% for RL. The variation for RL was even higher when the analysis was done separately for the inspiratory and expiratory phase. CL and VT had good reproducibility (ICC > 0.9), while RL was significantly less reproducible (ICC < 0.75). Measurements obtained from mechanical breaths had less variability than from spontaneous breaths, ranging from 8% to 15% for CL and VT, and from 13% to 21% for RL. Reproducibility assessed by the ICC was good for most measurements during mechanical breaths. The variability and reproducibility of measurements were similar for both methods of analysis during mechanical ventilation, but during spontaneous breathing variability was larger with the MW method than with LR analysis. We concluded that VT and CL were reproducible during spontaneous and mechanical breathing. However, RL measurements were reproducible only during mechanical ventilation. The high variability of RL in spontaneously breathing preterm infants may reduce the clinical usefulness of this measurement for individual patients.

Humans↗

PubMed1999

The reproducibility of videokeratoscope measurements as applied to the human cornea.

To be useful in contact lens fitting, the videokeratoscope (VK) must be able to provide the practitioner with credible data on the vertex radius and central topography, or 'shape, of the patient's cornea. For this purpose, it is desirable that the measured value of the former should be credible at the level of 0.05 mm. In order to examine the accuracy, repeatability and reproducibility of the corneal dimensions provided by the videokeratoscope, eight eyes were measured on four different EyeSys systems at four independent sites. The order of measurement was random at each site. This amounted to a balanced uniform-level precision experiment ('ring test') of the VK instruments as defined in International Standard ISO 5725. The resulting data were analysed using the statistical procedures given in this Standard to provide a formal statement of the measurement precision of the EyeSys VK system. Based on this study, the estimated measurement precision of the EyeSys videokeratoscope as applied to the latter principal meridian of the normal human cornea is: Vertex radius: repeatability standard deviation, S(R)=0.0805, reproducibility standard deviation, S(R)=0.1041. p value: repeatability standard deviation, S(r)=0.0473, reproducibility standard deviation, S(R)=0.0574. The estimated measurement precision for the steeper principal meridian is: Vertex radius: repeatability standard deviation, S(r)=0.0771; reproducibility standard deviation, S(R)=0.1015. p value: repeatability standard deviation, S(R)=0.0698; reproducibility standard deviation, S(R)=0.0749.

Journal Article↗

PubMed2006

Sex ratio determination in bovine semen: a new approach by quantitative real time PCR.

Sex preselection of livestock offspring in cattle represents, nowadays, a big potential for genetic improvement and market demand satisfaction. Sperm sorting by flow cytometer provides a powerful tool for artificial insemination and production of predefined sexed embryos but, an accurate verification of the yield of sperm separation remains essential for a field application of this technique or for improvement and validation of other related semen sexing technologies. In this work a new method for the determination of the proportion of X- and Y-bearing spermatozoa in bovine semen sample was developed by real time PCR. Two sets of primers and internal TaqMan probes were designed on specific X- and Y-chromosome genes. To allow a direct quantification, a standard reference was established using two plasmid cDNA clones (ratio 1:1) for the specific gene targets. The method was validated by a series of accuracy, repeatability and reproducibility assays and by testing two sets of sorted and unsorted semen samples. A high degree of accuracy (98.9%), repeatability (CV=2.58%) and reproducibility (CV=2.57%) was shown. The results of X- and Y-sorted semen samples analysed by real time PCR and by flow cytometric reanalysis showed no significant difference (P>0.05). The evaluation of X-chromosome bearing sperms content in unsorted samples showed an average of 51.11+/-0.56% for ejaculates and 50.17+/-0.58% for the commercial semen. This new method for quantification of the sexual chromosome content in spermatozoa demonstrated to be rapid and reliable, providing a valid support to the sperm sexing technologies.

Animals↗

PubMed1994

Fluorescent-based typing of the two short tandem repeat loci HUMTH01 and HUMACTBP2: reproducibility of size measurements and genetic variation in the Swedish population.

The aim of this study was to investigate the reproducibility of genetic typing of two tetrameric short tandem repeat (STR) loci and the extent of genetic variation in the Swedish population. An automated, fluorescent-based Applied Biosystems 373A sequencer was used for typing of the HUMTH01 and HUMACTBP2 loci (also named SE33). The former locus has seven alleles in the size range of 154-174 bp, while the latter is a complex locus with more than 32 alleles in the range of 227-316 bp. Using different fluorescent dyes, polymerase chain reaction (PCR) products from the two STR loci were sized in one lane using an internal size standard. In order to compare within- and between-gel reproducibility of fragment size estimates, a control sample was typed three times on each of 20 gels. Within the gel, the standard deviation (SD) of fragment size variability was less than 0.1 bp for four fragment sizes between 158-291 bp. Standard deviations between gels were slightly higher for the two shorter fragment sizes (HUMTH01), while the larger fragments varied between 0.3 and 0.4 bp (HUMACTBP2). The amount of genetic variation was investigated in samples from three Swedish cities (n = 301). Seven alleles were found at HUMTH01 and the observed heterozygosity was 0.77. At the HUMACTBP2 locus more than thirty alleles were found and the observed heterozygosity was 0.96. The observed genotype frequencies at HUMTH01 and HUMACTBP2 did not deviate significantly from Hardy-Weinberg expectations. No indication of a significant excess of homozygotes was found at any of the loci. We conclude that both HUMTH01 and HUMACTBP2 can be reliably typed using the method described. However, the latter locus requires an allelic ladder to be run on each gel.

Alleles↗

PubMed2004

Assessing the reliability of a digital preparation assistant system used in dental education.

Use of a digital preparation assistant system may improve considerably the quality of preclinical dental education, provided the system works reliably. Thus, the purpose of this pilot study was to quantitatively assess the reliability of a new preclinical digital preparation assistant system (PREPassist, KaVo, Germany). The system was used to repeatedly scan four different unprepared and four different prepared teeth both with and without repositioning. Corresponding measurements were made to quantify accuracy, repeatability, and reproducibility. This was done by estimating the measurement error. Based on this estimation, respective limits of agreement were calculated. We used these ranges, along with assessments of the measurement's accuracy, to judge whether the results satisfy our expectations for clinically acceptable measurements. For preclinical laboratory instruction, the results indicate an acceptable accuracy (mean accuracy of 89 microm) of the measurements. This assessment applies as well to repeatability, given by the range of the respective limits of agreement (range <200 microm). However, in the case of reproducibility, the limits revealed discrepancies of practical importance (range >200 microm). Reproducibility of tooth repositioning in the available mounting device is unacceptable for preclinical laboratory instruction because of the observed range >200 microm. Thus, there is a need for the manufacture of new and more reliable mounting devices because reproducibility procedures are mostly encountered in preclinical instruction in restorative techniques. In contrast to reproducibility, accuracy and repeatability are acceptable for practical purposes. Balancing advantages and disadvantages, we conclude that, in general, the PREPassist system delivers reliable results.

Computer Simulation↗

PubMed2005

Multielement trace determination in SiC powders: assessment of interlaboratory comparisons aimed at the validation and standardization of analytical procedures with direct solid sampling based on ETV ICP OES and DC arc OES.

The members of the committee NMP 264 "Chemical analysis of non-oxidic raw and basic materials" of the German Standards Institute (DIN) have organized two interlaboratory comparisons for multielement determination of trace elements in silicon carbide (SiC) powders via direct solid sampling methods. One of the interlaboratory comparisons was based on the application of inductively coupled plasma optical emission spectrometry with electrothermal vaporization (ETV ICP OES), and the other on the application of optical emission spectrometry with direct current arc (DC arc OES). The interlaboratory comparisons were organized and performed in the framework of the development of two standards related to "the determination of mass fractions of metallic impurities in powders and grain sizes of ceramic raw and basic materials" by both methods. SiC powders were used as typical examples of this category of material. The aim of the interlaboratory comparisons was to determine the repeatability and reproducibility of both analytical methods to be standardized. This was an important contribution to the practical applicability of both draft standards. Eight laboratories participated in the interlaboratory comparison with ETV ICP OES and nine in the interlaboratory comparison with DC arc OES. Ten analytes were investigated by ETV ICP OES and eleven by DC arc OES. Six different SiC powders were used for the calibration. The mass fractions of their relevant trace elements were determined after wet chemical digestion. All participants followed the analytical requirements described in the draft standards. In the calculation process, three of the calibration materials were used successively as analytical samples. This was managed in the following manner: the material that had just been used as the analytical sample was excluded from the calibration, so the five other materials were used to establish the calibration plot. The results from the interlaboratory comparisons were summarized and used to determine the repeatability and the reproducibility (expressed as standard deviations) of both methods. The calculation was carried out according to the related standard. The results are specified and discussed in this paper, as are the optimized analytical conditions determined and used by the authors of this paper. For both methods, the repeatability relative standard deviations were <25%, usually ~10%, and the reproducibility relative standard deviations were <35%, usually ~15%. These results were regarded as satifactory for both methods intended for rapid analysis of materials for which decomposition is difficult and time-consuming. Also described are some results from an interlaboratory comparison used to certify one of the materials that had been previously used for validation in both interlaboratory comparisons. Thirty laboratories (from eight countries) participated in this interlaboratory comparison for certification. As examples, accepted results are shown from laboratories that used ETV ICP OES or DC arc OES and had performed calibrations by using solutions or oxides, respectively. The certified mass fractions of the certified reference materials were also compared with the mass fractions determined in the interlaboratory comparisons performed within the framework of method standardization. Good agreement was found for most of the analytes.

Calibration↗

PubMedDate not supplied

Liquid chromatographic method for determination of aflatoxins B1, B2, G1, and G2 in corn and peanut products: collaborative study.

A collaborative study of a liquid chromatographic method for the determination of aflatoxins B1, B2, G1, and G2 was conducted in laboratories located in the United States, Canada, South Africa, and Switzerland. Twenty-one artificially contaminated raw peanuts, peanut butter, and corn samples containing varying amounts of aflatoxins B1, B2, G1, and G2 were distributed to participating laboratories. The test portion was extracted with methanol-0.1N HCl (4 + 1), filtered, defatted with hexane, and then partitioned with methylene chloride. The concentrated extract was passed through a silica gel column. Aflatoxins B1 and G1 were derivatized with trifluoroacetic acid, and the individual aflatoxins were determined by reverse-phase liquid chromatography with fluorescence detection. Statistical analysis of the data was performed to determine or confirm outliers, and to compute repeatability and reproducibility of the method. For corn, relative standard deviations for repeatability (RSDr) for aflatoxin B1 ranged from 27.2 to 8.3% for contamination levels from 5 through 50 ng/g. For raw peanuts and peanut butter, RSDr values for aflatoxin B1 were 35.0 to 41.2% and 11.2 to 19.1%, respectively, for contamination levels from 5 through 25 ng/g. RSDr values for aflatoxins B2, G1, and G2 were similar. Relative standard deviations for reproducibility (RSDr) for aflatoxin B1 ranged from 15.8 to 38.4%, 24.4 to 33.4%, and 43.9 to 54.0% for corn, peanut butter, and raw peanuts, respectively. The method has been adopted official first action for the determination of aflatoxins B1, B2, G1, and G2 in peanut butter and corn at concentrations greater than or equal to 13 ng total aflatoxins/g.

Aflatoxin B1↗

PubMed2006

[Determination of galactooligosaccharide in syrups by high performance ion exchange chromatography method].

OBJECTIVE: The gradient procedure was developed based on AOAC 2001.02 to determine galactooligosaccharide (soluble dietary fiber with low molecular weight) by high performance ion exchange chromatography with pulsed amperometric detection. METHODS: In the present study, the modified gradient procedure was used to separate the mixed standard on a CarboPac PA1 (2mm x 250mm) anion exchange column. The galactooligosaccharide in syrups were quantified and the repeatability and reproducibility of the modified method were also evaluated. RESULTS: Galactose, glucose, sucrose, fructose and lactose were successfully separated. The galacto oligosaccharides contents in syrups of intra-assay were (49.59 +/- 3.34), (46.55 +/- 2.61) and (56.26 +/- 3.13)g/100g, RSD value were 6.73%, 5.62% and 5.56% respectively. RSD value for galactooligosaccharide of inter-assay in syrup 1 was 4.73%. CONCLUSIONS: Galactose and glucose were separated well and galactose was determined more accurately. the repeatability and the reproducibility of the modified method were excellent. This method can be used for GOS determination.

Chromatography, Ion Exchange↗

PubMed1997

Intraimage reproducibility of measurements in the macular area using a computerized system.

An accurate analysis of the morphological changes which take place during pathological processes of the posterior pole is important for a correct diagnosis and therapeutic approach. The purpose of the study was to determine the intraobserver and interobserver reproducibility of the Image-net system 100 (Topcon, Japan) to take measurements on the retina. The program 'Linear/Areal Measurement functions' of Image-net system 100 which is an image digitalization technique, was tested. Twelve patients were consecutively selected from the patients of the Retina Center of the Department of Ophthalmology, University of Genoa. Three images of each eye were taken from each subject and only the best image was used in this study. The intraobserver and interobserver reproducibility of both the distance between two pre-set points (linear measurement), and the perimeter and area of preselected retinal zones were calculated. The repeatability (or intraobserver reproducibility) of the linear sizes was measured by the coefficient of variation and ranged from 0.32% to 7.38%, while the interobserver reproducibility ranged from 0.46% to 5.22%. The repeatability and reproducibility of the perimeters ranged from 0.72% to 9.63% and from 0.6% to 5.7%, respectively, while the repeatability and reproducibility of the areas ranged from 0.72% to 9.63% and from 0.6% to 5.7%, respectively. Although the results were quite good, the quality of the image of the fundus and the number of observers influenced the coefficient of variation; furthermore, the anatomy of the areas to be measured and the computer 'mouse' could increase the value of the coefficient of variation.

Angiography, Digital Subtraction↗

PubMed1978

Reproducibility and comparative analysis of repeated intravenous and oral glucose tolerance tests.

We have developed a methodology for measuring the reproducibility of the oral glucose tolerance test (OGTT) and the intravenous glucose tolerance test (IVGTT) in normal subjects and in offspring of conjugal diabetic parents. Both groups of subjects revealed more striking correlations of several parameters of blood glucose and insulin secretion between two IVGTTs than between two OGTTs. Employing arbitrary criteria, we calculated a "reproducibility index" as a quantitative measure of blood glucose variability in each subject. No significant difference was found in the reproducibility of OGTT versus IVGTT, nor in normals versus the offspring. Only about 50 per cent of the tests in normals and in the offspring could be considered to be "reproducible." The offspring revealed greater correlations of several parameters, particularly insulin secretion, between the two IVGTTs and between the two OGTTs as compared with the normal group. However, the blood glucose variations tended to be considerably greater in the offspring from one to the other test.

Administration, Oral↗

PubMed1996

Accuracy in determining intraocular lens dioptric power assessed by interlaboratory tests.

PURPOSE: To describe a testing program conducted by a standards group as a guide for setting international tolerances for intraocular lens (IOL) dioptric power. SETTING: Multicenter study. METHODS: Seven biconvex, poly(methyl methacrylate) IOLs ranging in power from 10.00 through 30.00 diopter (D) were circulated among nine participating laboratories experienced in IOL optical measurements. Each laboratory performed repeated optical tests to determine dioptric power. These results were analyzed for repeatability and reproducibility in accordance with methods specified by the International Organization for Standardization. RESULTS: Intralaboratory repeatability was less than 0.5% of the dioptric power, and interlaboratory reproducibility, when following a normalized procedure for correction and conversion, was less than 1.0% of the dioptric power. CONCLUSION: Tolerance limits of +/0 0.30 D in the range 0 to 15.00 D, +/- 0.40 D for 15.50 to 25.00 D, and +/- 0.50 D for 25.50 to 30.00 D have been proposed as an international standard for IOLs. The contribution of IOL power error within the limits of the standard are estimated to contribute less than 1.0% to the total error in postoperative refractive prediction.

Lenses, Intraocular↗

PubMed1996

Prediction of FCC gasoline octane numbers using FT-MIR and PLS.

A method for predicting "octane numbers" (RON and MON) in fluid catalytic cracking (FCC) gasolines is proposed. Using FT-MIR and PLS, improvements have been obtained in sample throughput, reduced delay times, accuracy (repeatability and reproducibility), amounts of samples and reagents and environmental working conditions when compared with current standard methods. A total number of 140 daily production samples were taken; and from there, a learning group was prepared (44 samples); a validation set (96 samples) was prepared, as well. Sample spectra were recorded from 4000 to 600 cm(-1) at 4 cm(-1) intervals (traditional sealed NaCl cells). The PLS technique was used in its two variants (1 and 2-block). Both provided similar results. Their predictive characteristics are very good: SEP(RON)=0.38; SEP(MON)=0.40; repeatability <0.1 O.N.; reproducibility <0.3 O.N. (SEP=Standard Error of Prediction).

Journal Article↗

PubMed1987

Gastric acid secretory capacity falls after repeated within-day pentagastrin testing in fed subjects.

Between-day pentagastrin testing yields highly reproducible stimulated gastric acid output values, but little is known of the reproducibility of repeated within-day pentagastrin tests. We have performed three pentagastrin tests within the 1 day in nine healthy subjects. Within-day tests were 6 hours apart; the first followed an overnight fast and the second and third were both 4 hours after a substantial meal. A further test was performed the following morning, again after an overnight fast, which allowed comparison of within-day and between-day testing. In the second and third within-day tests there was a marked decrease of stimulated gastric acid output, with both maximal and peak acid output decreased to approximately half of the value of the first test (P less than 0.01). By contrast there were no significant differences in the acid output values obtained in between-day tests (both following an overnight fast). Possible mechanisms for the decreased output on repeated within-day testing include alterations in the sensitivity of the gastrin receptor, or some neurohumoral influence secondary to the preceding meal. Future studies of the duration of action of drugs affecting acid secretion may need to take account of these findings.

Adult↗

PubMedDate not supplied

Performance evaluation of direct forced-air total solids and Kjeldahl total nitrogen methods: 1990 through 1995.

Results from collaborative studies of the performance of the direct forced-air oven-drying method for determination of milk total solids content (AOAC Method 990.20) and the Kjeldahl total nitrogen method for determination of milk total nitrogen content (AOAC Method 991.20) were published in 1989 and 1990, respectively. Method performance was characterized by using the harmonized ISO/IU-PAC/AOAC guidelines for method validation, and the methods now have final action status. During 1990 through 1995, the split sample collaborative study format was used to monitor the performance of these methods as part of a multilaboratory quality assurance program. Seven blind duplicate milk materials were sent from a central laboratory once every 2 months to participating laboratories. Data were analyzed with the same statistical procedures used in the original collaborative studies. Compared with the original collaborative study, the repeatability and reproducibility of the oven-drying method improved over time. For the Kjeldahl total nitrogen method, within-laboratory repeatability improved slightly, whereas between-laboratory reproducibility was similar to but not always as good as in the original study. The results demonstrate that the statistical protocol for collaborative studies can be used effectively as the basis for a multilaboratory quality assurance program and that the method performance achieved in a collaborative study can be maintained and even improved with time.

Animals↗