Lifetime probabilities of needing an organ transplant versus donating an organ after death.

The lifetime probabilities of becoming a deceased organ donor and requiring or receiving an organ transplant are unknown. An actuarial analysis was performed in a representative Canadian sample. Using Canadian organ donation data 1999-2007, provincial waiting list and population census data, actuarial rates were produced that provide the probabilities, by age band and gender, of (1) becoming a deceased organ donor, (2) needing an organ transplant and (3) receiving all organs needed. Regardless of age, the lifetime probability of needing a transplant for males is approximately twice that of females. Depending on age, Canadians are five to six times more likely to need an organ transplant than to become a deceased organ donor. The lifetime probabilities of not receiving a required organ transplant, expressed as a percentage of individuals on the waiting list, ranges from approximately 30% at birth, 20 years and 40 years to approximately 40% at 60 years. Across provinces and genders, Canadians at all ages are much more likely to need an organ transplant than to become an organ donor. Approximately one-third of those in need of a transplant will never receive one. How this information may influence organ donation decisions is currently under study.

Searching through subsets: a test of the visual indexing hypothesis.

This paper presents three experiments investigating the claim that the visual system utilizes a primitive indexing mechanism (sometimes called FINSTS; Pylyshyn, 1989) to make non-contiguous features directly accessible for further visual processing. This claim is investigated using a variant of the conjunction search task in which subjects search among a subset of the items in a conjunction search display for targets defined by a conjunction of colour and orientation. The members of the subset were identified by virtue of the late onset of the objects' place-holders. The cued subset was manipulated to include either homogeneous distractors or mixed distractors. Observers were able to select a subset of three items from among fifteen for further processing (Experiment 1); furthermore, a reaction time advantage for homogeneous subsets over mixed subsets was observed, indicating that more than one of the subset is selected for further specialized processing. The homogeneous subset advantage held for subsets of two to five items (Experiment 2), and the time required to process the cued subset did not increase with increased dispersion of the items (Experiment 3). These results support the basic claim of the indexing theory: the claim that multiple visual indexes are used in selecting objects for visual processing.

A critique of an evaluation of the impact of hospital bed closures in Winnipeg, Canada: lessons to be learned from evaluation research methods.

In the last few years, the continuing increases in health care expenditures have led to a call for greater accountability in health care and have spurred evaluative research into the area of health care policy. Yet the challenge has been to develop health care policy evaluations that maximize the rigor of the evaluation process within the constraints and limitations of evaluation milieus. This paper describes the principles of evaluation research and, using the example of a study evaluating the impact of hospital bed closures on community health status in Winnipeg, Canada, demonstrates the epistemological, methodological and interpretive problems that can occur when these principles are not followed. The conclusions are that studies which fail to outline the causal links between policy actions and outcomes, and use designs and methods which threaten internal and external validity, are limited in their abilities to elucidate the impact of health care policy changes.

A decision-making aid for long-term care waiting list policies: modelling first-come, first-served vs. needs-based criteria.

A chronic care hospital in London, Ontario, was faced with the question of whether to continue to admit applicants on a first-come, first-served basis, or to implement a needs-based admission criterion To provide information relevant to this decision, a simple computer modelling technique was used to model the waiting list under both policies. Analysis of the results indicated substantial variability in the need for care demonstrated by waiting list applicants, and individual placement priority under the two schemes. Descriptions of individuals affected by the proposed change in policy provided additional information. The information provided by the waiting list analysis contributed to the decision-making process about waiting list policy. The method used is applicable to waiting list management decisions in other institutions.

Multiple parallel access in visual attention.

It is widely accepted that there exists a region or locus of maximal resource allocation in visual perception--sometimes referred to as the spotlight of attention. We have argued that even if there is a single locus of processing, there must be multiple loci of parallel access--several places in the visual field must be indexed at once and these indexes can be used to determine where attention is allocated. We have carried out a variety of studies to support these ideas, including experiments showing that subjects can track multiple independent moving targets in a field of identical distractors, that the enhanced ability to detect changes occurring on these targets does not accrue to nontargets nor to items lying inside the convex polygon that they form (so that a zoom-lens of attention does not fit the data). We have used a visual search paradigm to show that (serial or parallel) search can be confined to a subset of indexed items and the layout of these items is of little importance. We have also studied the phenomenon known as subitizing and have shown that subitizing occurs only when items can be preattentively individuated and in those cases location precuing has little effect, compared with when counting occurs, which suggests that subitizing may be carried out by counting active indexes rather than items in the visual field. And finally we have run studies showing that a certain motion effect that is sensitive to attention can occur at multiple precued loci. We believe that this evidence suggests that there is an early preattentive stage in vision where a small number of salient items in the visual field are indexed and thereby made readily accessible for a variety of visual tasks.

The cost of visual filtering.

Speeded choice responses (reading or naming) to a relevant stimulus under conditions of spatial uncertainty are delayed by the simultaneous occurrence of other events. This "filtering cost" occurs despite high discriminability of target and distractors, which allows parallel detection of the target in search through the same displays. Reading is also delayed when the removal of irrelevant objects from the field coincides with the onset of the target. Filtering costs are caused by the processing of events rather than by the mere presence of irrelevant items. They are eliminated by advance information about the location of the target or by advance presentation of maintained distractors.