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PubMed1998

Statistical methods in epidemiology: a comparison of statistical methods to analyze dose-response and trend analysis in epidemiologic studies.

Evaluation of various statistical methods to describe accurately associations between exposures and disease are constantly being explored. Spline regression has been suggested as an alternative to using categorized variables in studies of disease etiology, as it uses all data points to estimate the shape of the association between a given exposure and disease outcome. It has been proposed that this method is especially beneficial when associations are concentrated in a small range of the overall distribution of the exposure. In this study, we use data from a large case-control study of colon cancer to evaluate associations obtained from logistic regression models that use spline regression for main exposure and confounder effects with those that use categorized variables for main exposure. Our results show that for variables for which the association appears to be linear, such as body size and dietary intake of calcium, fiber, and cholesterol, associations are similar when estimates are generated from spline or categorized variable models. For other variables, such as total energy intake, for which associations appear to be strongest in the upper end of the distribution, estimates of association appear to be conservative when using categorized variables. The data also suggest that selection of cut points for the categorized variables may have an impact on the associations observed. Spline regression appears to be useful to estimate the shape of the association between a given exposure and disease and may provide guidance as to the appropriateness of using categorized variables. The risk estimates from spline regression appear to be similar to those from traditional categorical methods. When effects are large or rapidly changing, spline models may more appropriately describe the association.

Adult↗
PubMed1983

A minimal apparatus method for counting bacteria: comparison with reference method in surveying beef carcasses at three commercial abattoirs.

In two surveys of three commercial abattoirs a minimal apparatus method for making bacterial counts, the "loop-tile' method, detected the same trends in bacterial numbers on beef carcasses as the ISO reference method applied to the same samples. Both methods showed the carcasses from one abattoir, that with an export license, to carry consistently higher numbers of bacteria, and one of the four sites sampled on each carcass to be consistently dirtier than the other three.

Abattoirs↗
PubMed1993

[Development of anti-Treponema pallidum-IgM antibodies detection methods using purified antigen--comparison with conventional methods].

Treponema pallidum subsp. pallidum Nichols (Tp) antigens were purified by centrifugation in the presence of Hypaque (sodium diatrizoate) or MgCl2. When the TPHA (Treponema pallidum hemagglutination) tests with crude and purified antigens were carried out in the sera of patients with untreated primary syphilis, the purification by MgCl2 resulted in enhanced sensitivity to Tp-specific IgM as the same as the purification by Hypaque. In addition, the SPHA (solid phase hemadsorption) test with the Hypaque-purified antigen to anti-Tp-IgM antibodies was carried out using the sera of patients with primary and secondary syphilis. Fifty-nine percent (27/46) of them showed positive for the crude antigen and 100% (46/46) for the purified antigen, indicating that sensitivity to anti Tp-IgM was clearly enhanced with the antigen purification. The captured Tp-IgM-RIA test with the purified antigen was also undertaken in 16 patients with primary syphilis, 31 patients with secondary syphilis and 73 patients with latent syphilis. All the patients in the former two groups were positive, while all of the patients in the latter group were negative. To elucidate the mechanism whereby the purification improves the sensitivity to anti-Tp-IgM antibodies, host-derived antibodies associated with crude and purified Tp cells were measured by a fluorescent antibody technique. As the results, a great amount of rabbit anti-Tp-IgM antibodies were found on the surface of the crude antigen, whereas only a trace amount was detected on the purified antigens.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibodies, Bacterial↗
PubMed1986

[Use of quantitative methods in cineangiocardiography: a comparison of 9 methods of motion analysis for the detection of regional function in patients with coronary heart disease].

In order to evaluate the usefulness of various quantitative methods for the assessment of regional left ventricular function, a total of 9 methods (3 hemiaxial models, 1 area model and 5 radial-axes models) were applied to the radiopaque ventriculograms of 16 patients with anterior wall infarction and 13 patients with posterior wall infarction. A series of 17 patients without clinical or angiographic evidence of heart disease were used as control group. While the hemiaxial methods were consistently found to be useful and reproducible, the area method did not provide significant additional information. The diagnostic accuracy was highest with the use of 2 radial-axes methods. The sensitivity and specificity data were 90% to 100% and 70% to 100%, respectively. The remaining 3 radial-axes methods were found to be of limited value since regional wall motion abnormalities were projected to the contralateral wall. Because of this methodological shortcoming these techniques may falsely indicate asynergy in areas with normal contraction patterns. This was reflected by high sensitivity but low specificity values. A feature of the latter 3 methods was the use of the gravity center of the end-systolic frame as the reference point. The position of this reference point is decisively influenced by the extent and localization of asynergy. These findings suggest that methods using the gravity center of the end-systolic frame should not be employed in the evaluation of regional left ventricular function. In general, some quantitative methods for assessing regional left ventricular function require a considerable expense for technical apparatus which is not always justified by the extent to which additional information is gained.

Angiocardiography↗
PubMed1996

Reliability of and comparisons among methods of measuring dissociated phoria.

Many methods of heterophoria measurement are available clinically. This paper reviews several studies which have examined the reliability of phoria measurements, and have compared various tests of phoria measurement. Different methods of data analysis make comparison of studies difficult. Two studies indicated 95% limits of agreement of 2 to 4 delta for reliability of modified Thorington, von Graefe, and Maddox rod phoria tests. Studies using correlational analysis to compare different measurement methods have found a high degree of association of the results of these methods. Studies using statistical methods assessing the agreement of test results found a high level of agreement among some tests and a low level of agreement among some tests. Some of the various phoria measurement methods differ in the technique used for dissociation, in the ability to control accommodation adequately, in the level of proximal convergence induced, or in the method by which the phoria is quantified. These differences can result in different phoria measurements on the same patient.

Humans↗
PubMed1980

Estimating the extra charges and prolongation of hospitalization due to nosocomial infections: a comparison of methods.

Estimates of the economic consequences of nosocomial infections were derived by studying the same patient population with two different methods: physician's assessment and comparisons of patients with nosocomial infection and those without, matched on five characteristics. Estimates of extra days and extra routine charges obtained by the comparison were about 2 1/2 times greater than those obtained by the physician's assessment (P less than 0.0001). Even when the match of patients was exact and measures were taken to avoid confounding, patients with nosocomial infection had more discharge diagnoses recorded (P = 0.02) and experienced more episodes of pulmonary embolism, renal failure, and death in the hospital than did their counterparts. These differences suggest that, despite careful matching, the members of the pairs were not comparable in their intrinsic predisposition to prolonged hospitalization. Unless patients can be matched on this prediposition, the estimates from a comparison study will be exaggerated.

Cost-Benefit Analysis↗
PubMed2002

Measurement equivalence: a comparison of methods based on confirmatory factor analysis and item response theory.

Current interest in the assessment of measurement equivalence emphasizes 2 major methods of analysis. The authors offer a comparison of a linear method (confirmatory factor analysis) and a nonlinear method (differential item and test functioning using item response theory) with an emphasis on their methodological similarities and differences. The 2 approaches test for the equality of true scores (or expected raw scores) across 2 populations when the latent (or factor) score is held constant. Both approaches can provide information about when measurement nonequivalence exists and the extent to which it is a problem. An empirical example is used to illustrate the 2 approaches.

Factor Analysis, Statistical↗
PubMed1995

Development of a simple and selective separation of 67Cu from irradiated zinc for use in antibody labelling: a comparison of methods.

A procedure for the production and separation of Cu isotopes from irradiated Zn was developed. Following a comparison of methods based on extraction, electrolysis and ion-exchange chromatography, a technique for the separation of Cu employing three ion-exchange matrices was developed which was simple, reproducible and hot cell-compatible. The specific activity of the final product was 37 MBq 67Cu/microgram Cu at EOB. The level of impurities was so low that no interference with antibody labelling was observed.

Antibodies↗
PubMed1988

Infectivity assay of bovine rotavirus: evaluation of plaque and end-point methods in comparison with immunofluorescent cell assay.

Three different methods, namely plaque assay, immunofluorescent cell (IFC) count and end-point dilution (TCID50) were evaluated for quantitative infectivity assay of the cell culture adapted UK strain of bovine rotavirus in secondary calf kidney (CK) cells and BGM cell line. Plaque and IFC count techniques were found equally efficient for infectivity titration of bovine rotavirus. Addition of trypsin into maintenance medium enhanced the sensitivity of the TCID50 method. Both CK and BGM cells served as efficient assay cells for infectivity assay of bovine rotavirus by IFC count and TCID50 methods, whereas, for plaque assay, only CK cells were found suitable.

Animals↗
PubMed1986

Multicentre evaluation of an enzymatic method for creatinine determination using a sensitive colour reagent.

A new enzymatic colorimetric method for the determination of creatinine in serum and urine (Creatinine PAP, Cat. No. 839434 and 836885, Boehringer Mannheim GmbH, Mannheim, FRG) was evaluated in 16 clinical chemistry laboratories and the manufacturer's testing laboratory. The test is based on the enzymatic degradation of creatinine and its reaction products by creatininase, creatinase and sarcosine oxidase. The H2O2 produced by the oxidation of sarcosine is determined using a modified Trinder reaction. The test can be carried out either manually or in mechanized analysers which enable the pipetting of a starter reagent to be made. The following results were obtained: Depending on the analyte concentration (range 40 to 1240 mumol/l), medians for the coefficients of variation were: 4.6-0.9% within-run and 6.4-2.8% between-day. At 546 nm the linear measuring range extended from 13 mumol/l (detection limit) to 1780 mumol/l, at 510 nm from 9 to 890 mumol/l. Recoveries in aqueous and human serum based standards as well as method comparisons with Fuller's earth methods and an enzymatic UV test indicate a high accuracy of this new enzymatic method in serum and urine. No interference was observed with haemolysed and lipaemic sera. This also applied to anticoagulants and to 36 drugs at therapeutic concentrations, with the exception of calcium dobesilate, which led to decreased values. Icteric samples containing 120-310 mumol/l bilirubin invariably led to decreased creatinine values (10-50 mumol/l lower). In a collaborative study substantially better interlaboratory agreement was observed with the new colorimetric enzymatic test than with the comparison methods (enzymatic UV test and various Jaffe procedures). In conclusion, this new enzymatic colorimetric test permits a precise and specific determination of creatinine in serum and urine. It makes a considerable contribution to improving the interlaboratory comparability of creatinine determinations and is suitable for routine use.

Bilirubin↗
PubMed1994

A comparison of methods for calculating DNA double-strand break induction frequency in mammalian cells by pulsed-field gel electrophoresis.

Pulsed-field electrophoresis (PFGE) has become one of the most widely used methods for the evaluation of radiation-induced DNA double-strand breaks (dsb). In most studies a simple quantification of DNA migration from the well in the gel has been used as the correlate with dsb formation. Here we have compared such a method, as calibrated with 125I-labelled UdR, with two methods which involved the analysis of the distribution of sizes of DNA fragments migrating in the gel. We conclude that the three methods produce similar absolute values for dsb induction frequency. It is not clear which is the single method of choice but the comparison of the analyses increases the information which can be derived from PFGE experiments.

Cobalt Radioisotopes↗
PubMed2005

A quantitative method for comparison of expression of alternatively spliced genes using different primer pairs.

In this paper we describe a novel two-step method for comparison of expression of alternatively spliced genes by quantitative PCR (QPCR) applying different primer pairs. As a model system we used rat decay accelerating factor (DAF; CD55) mRNA, which comprises three different isoforms: soluble (sDAF), transmembrane (tmDAF) and glycosyl-phosphatidylinositol (GPI) anchored (gpiDAF) forms. The first step was to prepare solid phase specific for each mRNA isoform and purify the three DAF-forms from total RNA. We then assessed amplification efficiency of primer pairs designed to recognise each of the isoforms using equimolar amounts of the three purified DAF mRNAs. The final step in our assay was to compare expression of the three DAF-isoforms in testis by QPCR taking into account the efficiency of their amplification to enable quantification. The RNA capture/QPCR method we described here can be used for quantifying the expression ratios of alternatively spliced mRNAs from a single gene or for direct comparison of expression of different genes.

Alternative Splicing↗
PubMed2000

A comparison of methods for measuring the antibody response in mice and cattle following vaccination against foot and mouth disease.

We present a comparison of methods for evaluating the potency of foot and mouth disease vaccine in the laboratory. The anti-FMDV antibodies (Ab) in vaccinated mice were tested by liquid phase (lp) ELISA, solid phase (sp) ELISA and virus neutralization (VN), and were compared with the Ab titres detected by lpELISA, which is the official test in Argentina for testing the potency of FMD vaccines and protection against a virulent challenge in cattle. The results demonstrated that it is possible to relate the Ab levels induced in vaccinated mice with both the Ab and protective responses elicited in cattle. Furthermore, it was found that the anti-FMDV Ab titres in mice detected by lpELISA 14 days after vaccination should be an accurate parameter for predicting the results of the challenge test in cattle. Thus, this test in mice appears to be an inexpensive and rapid alternative for testing FMD vaccines in cattle.

Animals↗