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Biomedical subjects

M J Goddard

Publications and source records attributed to M J Goddard.

44 records · Page 3Linked to original sources
PubMed1980

A statistical procedure for quality control in diagnostic laboratories.

The accuracy of results from any epidemiological project depends upon the performance of all stages of data collection and handling. One link in this chain may involve microscopic inspection of specimens and the purpose of this article is to describe means of assessing the accuracy of this stage. Two aspects merit consideration: the design of a sampling system and the collection and interpretation of the results. The importance of design is stressed, but the considerable variation in individual circumstances rules out a full treatment of the topic. A method of record keeping is described together with a method for graphical presentation of results. A procedure is outlined for detecting unacceptable performances and some of the statistical considerations are discussed.

Clinical Laboratory Techniques↗
PubMed1979

Estimating the duration of latency and survival time of snails with schistosomiasis.

By means of techniques of analyses of survival data developed for cancer trials it is possible to study aspects of the natural history of the infection of schistosomiasis on the intermediate host of transmission, the snail. The simultaneous study of three response variables is largely based on a model of Lagakos (1976). When using this approach in the schistosomiasis setting it seems inappropriate to assume that one process, the duration of latency, follows an exponential distribution. Thus this stage is modified to follow a normal distribution and the derivatives required to obtain maximum-likelihood estimates and approximate variances of all parameters are provided. Simple graphical tools for assessing the validity of distributional assumptions in survival data are available from industrial research. The reader's attention is drawn to a paper by Nelson (1972). The relevance and application of these methods to the current problem are described in Section 4. In the event that the times to death of prepatent and patent snails do not follow exponential distributions as assumed in the primary model, a further modification is introduced to enable either or both to follow Weibull densities. Lastly it is possible to adapt both the primary model of Section Three and the modified model of Section Five to allow for the inclusion of auxiliary variables or covariates. Again the required derivatives to obtain maximum likelihood estimates and approximate variances are provided.

Animals↗
PubMed1978

On Macdonald's model for schistosomiasis.

An attempt is made to reconstruct the specifics of the model in Macdonald's 1965 paper based on some manuscripts. The resulting model is not conclusive as discrepancies occur between this formulation and Macdonald's results. Assuming the formulation is adequate, the values of parameters yielding Macdonald's standard situation are provided. A way of studying the equilibrium behaviour of the model is outlined. The mathematical nature of the properties observed by Macdonald is studied. The model is altered to admit aggregated distributions of worms in hosts and to permit different death rates of infected and uninfected snails. The dynamics are found to depend strongly on the death rate of infected snails.

Animals↗
PubMed1977

On allowing for diagnostic imperfections in assessing effectiveness of treatment for Schistosomiasis.

Some possible effects of misdiagnosis for Schistosomiasis in epidemiological measurements are investigated. With greater chances of misdiagnosis for lower prevalence levels, expectations of control programmes might be reassessed. As prevalence decreases, the fraction of missed positives over all apparent negatives need not uniformly decrease. In control situations even perfect treatment rates may produce very small changes in prevalence and other indices of infectivity level.

Bayes Theorem↗