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W H Swallow

Publications and source records attributed to W H Swallow.

10 recordsLinked to original sources
PubMed2000

Use of binomial group testing in tests of hypotheses for classification or quantitative covariables.

In group testing, the test unit consists of a group of individuals. If the group test is positive, then one or more individuals in the group are assumed to be positive. A group observation in binomial group testing can be, say, the test result (positive or negative) for a pool of blood samples that come from several different individuals. It has been shown that, when the proportion (p) of infected individuals is low, group testing is often preferable to individual testing for identifying infected individuals and for estimating proportions of those infected. We extend the potential applications of group testing to hypothesis-testing problems wherein one wants to test for a relationship between p and a classification or quantitative covariable. Asymptotic relative efficiencies (AREs) of tests based on group testing versus the usual individual testing are obtained. The Pitman ARE strongly favors group testing in many cases. Small-sample results from simulation studies are given and are consistent with the large-sample (asymptotic) findings. We illustrate the potential advantages of group testing in hypothesis testing using HIV-1 seroprevalence data.

Adolescent↗
PubMed1999

Robustness of group testing in the estimation of proportions.

In binomial group testing, unlike one-at-a-time testing, the test unit consists of a group of individuals, and each group is declared to be defective or nondefective. A defective group is one that is presumed to include one or more defective (e.g., infected, positive) individuals and a nondefective group to contain only nondefective individuals. The usual binomial model considers the individuals being grouped as independent and identically distributed Bernoulli random variables. Under the binomial model and presuming that groups are tested and classified without error, it has been shown that, when the proportion of defective individuals is low, group testing is often preferable to individual testing for identifying infected individuals and for estimating proportions of defectives. We discuss the robustness of group testing for estimating proportions when the underlying assumptions of (i) no testing errors and (ii) independent individuals are violated. To evaluate the effect of these model violations, two dilution-effect models and a serial correlation model are considered. Group testing proved to be quite robust to serial correlation. In the presence of a dilution effect, smaller group sizes should be used, but most of the benefits of group testing can still be realized.

AIDS Serodiagnosis↗
PubMed1990

Using group testing to estimate a proportion, and to test the binomial model.

Group testing has been extensively studied as an efficient way to classify units as defective or satisfactory when the proportion (p) of defectives is small. It can also be used to estimate p, often substantially reducing the mean squared error (MSE) of p and cost per unit information. Group testing is useful for larger p in the estimation problem than in the classification problem, but for larger p more care must be taken in choosing the group size (k); k being too large not only increases MSE (p), but adversely affects the robustness of p to both errors in testing (misclassification) and errors in the assumed binomial model. Procedures that retest units from defective groups, if even feasible, are shown to reduce cost per unit information very little in the estimation problem, but can provide useful information for testing the model. Methods are given for using data from tests of unequal-sized groups to estimate p and for testing the validity of the binomial model.

Animals↗
PubMed1988

A qualitative UV spectroscopic method as an initial guide to source origins of polycyclic aromatic hydrocarbons.

A qualitative method is described, using ultraviolet spectroscopy, to determine the source origins of polycyclic aromatic hydrocarbons present in the environment. The technique takes advantage of the fact that aromatic compounds exhibit strong absorption in the ultraviolet region. It offers a fast and convenient alternative to other methods, which normally require extensive sample clean-up to avoid or limit interference from other materials during analysis. In contrast, this method requires only basic column chromatography to isolate the compounds of interest. Examples of the application of the technique are presented; the results are corroborated by those previously obtained by other methods.

Journal Article↗
PubMed1983

The metabolism of 7,12-dimethylbenz[a]anthracene and 7-hydroxymethyl-12-methylbenz[a]anthracene by rat liver and adrenal homogenates and by rat adrenocortical cells.

The metabolism of 3H-labelled 7,12-dimethylbenz[a]anthracene (DMBA) and of 7-hydroxymethyl-12-methylbenz[a]anthracene (7-OHM-12-MBA) into solvent- and water-soluble and protein-bound derivatives has been examined in rat liver and adrenal homogenates and in rat adrenocortical cells in culture. Although the overall extents of metabolism of the substrates by the two types of homogenate were similar, there was twice as much binding to protein in incubations with the 7-hydroxymethyl derivative. Rat adrenal cells in culture metabolized DMBA more extensively than 7-OHM-12-MBA and converted much more of the parent hydrocarbon into water-soluble derivatives. Both hydrocarbons were metabolized to yield dihydrodiols that were separated and identified by high performance liquid chromatography (HPLC). The 8,9-dihydrodiol was the major dihydrodiol formed from DMBA but, with 7-OHM-12-MBA as substrate, metabolism was diverted to the 10,11- and 3,4-positions in adrenal and hepatic preparations respectively. The viability of rat adrenocortical cells in culture, as measured by trypan blue exclusion, did not appear to be affected by treatment with DMBA, 7-OHM-12-MBA, the sulphate ester of 7-OHM-12-MBA or by 3,4-dihydro-3,4-dihydroxy-7-hydroxymethyl-12-methylbenz[a]anthracene.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1981

Oxidative hemoglobin breakdown induced by a rubber additive.

An antioxidant commonly present in black rubber, N-isopropyl-N'-phenyl-p-phenylenediamine (IPPD) caused very rapid oxidation and denaturation of purified hemoglobin. In the red cells, the reaction resulted in the formation of Heinz bodies, a decrease in reduced glutathione concentration, and stimulation of the hexose monophosphate shunt. IPPD appears therefore to have the potential to induce hemolysis in glucose-6-phosphate dehydrogenase deficiency. It would be expected to be more potent than most redox reagents of this type. It does not require further metabolism to be reactive, and its reactivity is similar to that of phenylhydrazine. But in particular since both IPPD and its oxidized form can oxidize hemoglobin it can act catalytically, and at low concentrations is much more effective than phenylhydrazine. Oxidation of blood stored in contact with rubber seals containing IPPD has been observed. It is also possible that prolonged contact of susceptible individuals either with rubber containing IPPD or to IPPD itself during rubber manufacture could result in hemolysis.

Anemia, Hemolytic↗