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P M Burrows

Publications and source records attributed to P M Burrows.

7 recordsLinked to original sources
PubMed1986

Variance weighting functions in radioimmunoassay calibration.

Software packages for radioimmunoassay calibration assume that expected counting rate is a function of ligand dose. Previous studies have indicated that variances of counting rate are also related to dose, but the structure of individual assays does not permit precise estimation of counting rate variances at individual doses. The method described here uses results from an accumulation of assays to characterize the relationship between mean and variance of counting rate, thus providing a variance weighting function for the calibration. Analysis of 140 cortisol assays, all with two replicates of each of 50 sources (9 standard doses, 3 quality control preps, and 38 unknowns), led to an asymmetric rising ogive relating variances to means of counting rates. A rectangular hyperbola provided an adequate characterization of this relationship in an accumulation of 21 testosterone assays. Relationships between mean and variance of counting rate in 19 growth hormone assays and 7 triiodothyronine assays were characterized by a straight line and a rising exponential curve, respectively. Calibration curves, such as the commonly adopted logistic ogive in relation to log dose, are fitted by weighted least squares to observed counts directly using empirical weights proportional to the reciprocal of estimated counting variance. The advantage of this method is that all observations contribute to the calibration in accordance with their merit.

Growth Hormone↗
PubMed1984

Use of experimental designs with quantitative ELISA.

Precise use of enzyme-linked immunosorbent assay (ELISA) as a quantitative technique depends on repeatability of color development and its measurement. Variation in measured response among wells, within and among microtiter plates, often precludes such precision. For example, plates with all wells treated uniformly exhibited unacceptable optical density differences in excess of 0.35 and 0.25 O.D. U among row and column averages, respectively. Arrangement of samples on plates according to classical experimental designs, with compact blocking features and two-dimensional control over spatial patterns, provides a possible remedy. Analysis of variations over uniformly treated plates demonstrated the potential for increased precision when such designs are used instead of random arrangements. Retrospective analysis of more than 100 tests performed with various experimental designs confirmed that this potential was realized when using Youden square and lattice square designs. Several designs appropriate for microtiter plates are presented and their conduct described.

Analysis of Variance↗
PubMed1981

Improved ELISA conditions for detection of plant viruses.

Clover yellow vein virus (CYVV) and homologous antisera were used to test effects of time and temperature on enzyme-linked immunosorbent assay (ELISA) in polystyrene substrate plates. Replicated lattice square and Youden square experimental designs were used to measure and account for variation in absorption values associated with sample position within polystyrene plates. Adsorption of coating antibody to polystyrene was relatively rapid, reaching optimum assay efficiency in 1 h at 5 degrees C when applied at 2.5 microgram/ml. Binding of antigen and enzyme-linked antibody (conjugate) in their respective steps during ELISA was also rapid. Incubation of antigen and conjugate for 2 h each was adequate to enable detection of 20 ng CYVV in a 100 microliter sample, but longer incubation of either reactant improved results. At this virus concentration, reduction in antigen incubation time by one-half could be compensated by doubling the conjugate incubation time and vice versa. Incubation of conjugates at 5 degrees C rather than 30 degrees C increased final ELISA readings (A400nm) more than two-fold. Substrate hydrolysis followed classic first order kinetics at room temperature. Greater efficiency of late antisera in ELISA was demonstrated by comparison of antisera produced relatively early and late during a rabbit's immune response. Alfalfa mosaic virus and peanut stunt virus with their homologous antisera were used to test the effects of antigen and conjugate incubation times for optimum assay efficiency. The results of these time course experiments with both viruses were similar to those obtained with CYVV. These time and temperature effects on ELISA should be applicable to most rabbit serum-virus combinations.

Antibodies, Viral↗
PubMed1976

Isozyme variability in species of the genus Drosophila. VIII. The alcohol dehydrogenase polymorphism in North Carolina populations of D. melanogaster.

Adult Drosophila melanogaster flies collected from populations broadly dispersed over ecological and geographic strata of North Carolina, and over a period of 4 years, were analyzed for alcohol dehydrogenase phenotypes by gel electrophoresis. Gene frequencies in spring-summer-fall field collections were remarkably stable over all strata. Two winter collections exhibited contrasting gene frequency changes. In one case the results are interpreted in terms of long-distance migration from Florida, while the other is explicable by assignment of a causal role to environmental factors which accompany the winter season.

Alcohol Oxidoreductases↗
PubMed1975

Variances of selection differentials in normal samples.

Standardized variances of selection differentials are defined in general and then considered in detail for the case of directional selection on the basis of normally distributed test scores. Symmetry properties, bounds and asymptotic values for the variances are derived. The results are used to investigate the variance of response to selection.

Mathematics↗