Screening without a "gold standard": the Hui-Walter paradigm revisited.

The authors consider screening populations with two screening tests but where a definitive "gold standard" is not readily available. They discuss a recent article in which a Bayesian approach to this problem is developed based on data that are sampled from a single population. It was subsequently pointed out that such inferences will not necessarily be accurate in the sense that standard errors for parameters may not decrease as n increases. This problem will generally occur when the data are insufficient to estimate all of the parameters as is the case when screening a single population with two tests. If both tests are applied to units sampled from two populations, however, this particular difficulty disappears. In this article the authors further examine this issue and develop an approach based on sampling two populations that yields increasingly accurate inferences as the sample size increases.

Dual screening.

We discuss the problem of screening a general population for characteristics such as HIV or drug use. Our main approach is Bayesian, which allows for the incorporation of prior information about parameters. In the particular problem we consider, there is currently no information in the data for estimating the sensitivity of the screening test, and consequently, the prevalence of the characteristic among screened negatives cannot be estimated from the collected data alone. Our inferences are straightforward to obtain using Gibbs sampling techniques, and they are valid for large or small samples and for arbitrary prevalence or accuracy of screening tests. We also develop the maximum-likelihood approach using the EM algorithm.

The faculty fellowship program: uniting service and education.

The outcomes of the pilot year for this project met the goals of increased faculty clinical skills, increased nursing personnel at the unit level and the completion of specified projects based on identified clinical needs. Continued development of the Faculty Fellowship Program will yield further opportunity to study benefits, such as increased student performance in the acute care setting, increased recruitment of graduate nurses and improved integration of nursing education and service in addressing health care issues.

Optimal designs for clinical trials with dichotomous responses.

We consider two-stage designs for clinical trials that involve two treatments with dichotomous responses. The first is the information-gathering stage; the treatment chosen as the better from first stage and prior data is used exclusively in the second stage. Determination of treatment allocation in the first stage results from weighing the anticipated gain in information with effective treatment; the objective is to maximize the expected number of successes in the entire trial. This is in contrast to randomized controlled trials with the restricted objective of obtaining information concerning treatment differences. We allow the length of the first stage to be arbitrary and fixed in advance, or optimized as a function of prior information and the 'patient horizon'. We can regard this patient horizon as either the number of patients in the trial or the number who have the condition under treatment. We consider two forms of prior information: both success probabilities known but the better of the two treatments is unknown, and one success probability known whereas the other has an arbitrary distribution. In many instances of the latter case the optimal first stage size is of the order of the square root of the patient horizon.

Responsiveness of pre- and non-delinquents to incentive aspects of a reinforcing event.

A learning task, a six-position modification of a Fellows (1967) sequence, was used to examine the differences in responsiveness to symbolic and tangible incentives with 24 pre-delinquent and 25 non-delinquent 15-yr.-old boys. Under the low-incentive condition, only the symbolic incentive was available while under the high-incentive condition a symbolic and material reinforcer was employed. The high-incentive condition had no significant effect on the non-delinquents but did significantly affect the delinquents. Also, the high-incentive delinquent group performed similarly to both non-delinquent groups. Recommendations for research are given.