Search PubMed⌕ Search

Biomedical subjects

J A Garrett

Publications and source records attributed to J A Garrett.

17 recordsLinked to original sources
PubMed2002

Sensitivity of two-stage sampling to detect sheep biting lice (Bovicola ovis) in infested flocks.

The sampling distribution of Bovicola ovis (Schrank) on sheep was examined in two flocks, one with a light and one with a heavy infestation of lice. The derived distributions were used to calculate the sensitivity of detecting lice on individual sheep and in flocks by fleece parting regimes that varied in number of parts per animal and number of sheep per flock, different scenarios of flock sizes, proportion infested and louse density were examined. Lice were aggregated among fleece partings in the heavily infested flock and described by a negative binomial distribution with k values between 0.3 and 1.92. The distribution was indistinguishable from Poisson in the lightly infested flock. The assumed distribution had little effect on sensitivity, except when only one fleece part per animal was examined. On individual sheep where louse density was 0.5 per 10 cm part or greater, there were only marginal gains from inspecting more than 10 parts per animal. Increasing the number of sheep inspected always increased sensitivity more than increasing number of parts per sheep by an equivalent amount. This advantage was greatest in situations where a low proportion of sheep in the flock were infested with a high density of lice, and less where a low proportion of sheep were infested with a low density of lice, or a high proportion of sheep were infested with a high density of lice.

Animals↗
PubMed2001

Some issues in resolution of diagnostic tests using an imperfect gold standard.

As a subject's true disease status is seldom known with certainty, it is necessary to compare the performance of new diagnostic tests with those of a currently accepted but imperfect 'gold standard'. Errors made by the gold standard mean that the sensitivity and specificity calculated for the new test are biased, and do not correctly estimate the new method's sensitivity and specificity. The traditional approach to this problem was 'discrepant resolution', in which the subjects for whom the two methods disagreed were subjected to a third 'resolver' test. Recent work has pointed out that this does not automatically solve the problem. A sounder approach goes beyond the discordant test results and tests at least some of the subjects with concordant results with the resolver also. This leaves some issues unresolved. One is the basic question of the direction of biases in various estimators. We point out that this question does not have a simple universal answer. Another issue, if one is to test a sample of the subjects with concordant results rather than all cases, is how to compute estimates and standard errors of the measures of test performance, notably sensitivity and specificity of the test method relative to the resolver. Expressions for these standard errors are given and illustrated with a numeric example. It is shown that using just a sample of subjects with concordant results may lead to great savings in assays. The design issue of how many concordant cells to test depends on the numbers of concordants and discordants. The formulae given show how to evaluate impact of different choices for these numbers and hence settle on a design that gives the required precision of estimates.

Chlamydia Infections↗
PubMed1996

A comparison of the Johnson Intervention with four other methods of referral to outpatient treatment.

The Johnson Intervention is a therapeutic technique in which members of the person's social network confront him or her about the damage the drinking or drug use has caused and the action they will take if treatment is refused. It is highly effective in engaging and retaining clients in inpatient treatment, but, since initial evaluations, two trends have emerged in the field. First, there has been an increase in the use of outpatient treatment and, second, a number of variations of the Johnson Intervention have been developed. The purpose of this study was to compare the effectiveness of the Johnson Intervention with four other methods of referral to outpatient treatment. The other methods included two naturally occurring types of referral (coerced and non-coerced) and two less intense and less costly variations of the Intervention (Unrehearsed and Unsupervised). Effectiveness was determined by both entry into and completion of treatment. A retrospective study was conducted on a sample of 331 cases drawn from an alcohol and other drug treatment agency. Those who had undergone the Johnson Intervention were more likely to enter treatment than those in any of the four other groups. Of those that entered treatment, the Johnson Intervention and the coerced referral groups were equally likely to complete treatment, and both groups were more likely to complete treatment than those in the other three types of referral. Although the Johnson Intervention was the most effective, the variations did show some measure of success and can be viewed as part of an Intervention continuum.

Adult↗
PubMed1996

The Johnson Intervention and relapse during outpatient treatment.

The Johnson Intervention is a therapeutic technique in which members of a person's social network confront him or her about the damage that drinking and drug use has caused and the action they will take if he or she does not enter treatment. Previously, we evaluated the effectiveness of the Johnson Intervention at engaging and retaining clients in outpatient alcohol and other drug (AOD) treatment by comparing it to four other methods of referral. Although individuals who undergo a Johnson Intervention are most likely to enter treatment, the power of the Johnson Intervention to retain clients deteriorates over the course of treatment, as indicated by their diminished likelihood of completing. Given that abstinence from alcohol and other drugs is one of the first expectations placed on clients, we compared the Johnson Intervention to the other types of referral to evaluate the role of relapse during treatment. In a secondary analysis of 210 cases, we found relapse rates across the five types of referral ranged from 38% to 79%. Those in the Johnson Intervention group were more likely to relapse than three of the four other groups and, across all groups, those who relapsed were less likely to complete treatment. In spite of its high relapse rate, the Johnson Intervention is very effective in retaining those who relapse because it is very effective retaining all clients, whether they relapse or not.

Adult↗
PubMed1991

Assessment criteria for diagnostic imaging technologies.

Expensive diagnostic imaging technologies need to be assessed. Assessment is most difficult with new technologies. Rapid technical change creates pressure for widespread provision because of apparently self-evident advantages. For the health care provider, technology assessment is of central importance. Timing is crucial; economic and clinical studies have to be carried out simultaneously; and studies must be broadly based. Assessment should be carried out only on properly selected technologies. Apart from picture archiving and communication systems, existing expensive diagnostic imaging technologies are now so mature that assessment is concerned mainly with costs and benefits. To be provided, a technology needs to be effective, economic, appropriate and needed. The history of computed tomography illustrates technology assessment from innovation to routine application. Technology assessment also provides essential guidance for equipment selection. Different regulations and controls, explicit or implicit, exist in different countries. There are special requirements for technology assessment in each country according to overall health requirements and policies. The main contemporary challenges are the correct selection of equipment for assessment, and the development of predictive methods of assessment.

Diagnostic Imaging↗
PubMed1990

Meeting the international standard ISO 9002/BS5750.

In this paper we outline the rationale for applying British Standard BS5750 to a medical equipment management service and introduce some of the concepts of the standard as they apply to this field. We see this application as essential in today's legal and commercial environment and indicate the ways in which this work is being carried forward by the Medical Equipment Management Organisation into total quality management systems.

Equipment Safety↗
PubMed1989

Hearing loss and otitis media on Guam: impact of professional services.

In less than two decades, there has been a dramatic reduction in the prevalence of otitis media and perforations among Guam's school-aged children. In addition, hearing loss due to chronic middle ear disease as a cause of disqualification from military service has dropped from a first rank order cause to next-to-last. However, there has been no reduction in the prevalence of otitis media in the preschool population. The reduction in chronic ear disease is the result of improved access to primary care, intensive hearing screening, wide availability of audiologic diagnostic and follow-up services, and comprehensive otologic care. It is essential that these services continue to be available to Guam's children to avoid a reversal of these dramatic gains. Attention must now focus on how to achieve similar gains for Micronesian children who remain restricted in their access to these resources.

Adolescent↗
PubMed1975

Optimal conditions for the growth of malignant human and animal cell populations in immunosuppressed mice.

Immunosuppressed mice have been used to support the growth of xenogeneic human and animal malignant cell populations. The optimal conditions for tumor growth are neonatal thymectomy coupled with antithymocyte serum or thymectomy, followed by whole-body irradiation and bone marrow reconstitution. When mice are inoculated with a mixture of normal and malignant cells, the malignant cells have a selective advantage. No such selectivity is found when the mixed populations are grown in vitro. Human tumors may also be grown in immunosuppressed mice. These tumors retain the organization of the original tumor in the human host. The advantages of this system to cancer researchers are discussed.

Animals↗
PubMedDate not supplied

Equipment management in practice.

This article describes the setting up, funding and organization of an in-house equipment management service in the Bristol & Weston Health Authority. Existing resources were redeployed to form the present service. The range of equipment now maintained under the auspices of the Medical Physics Bioengineering Group has a capital value of 12 million pounds. All work is costed and a charge made to the client for whom work is carried out. A team of 27 medical physics technicians and three graduate engineers are maintained from this source of income. This method of funding is now making way for a system of job costing which will provide a basis for comparison with an outside service.

Biomedical Engineering↗