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C J Schwarz

Publications and source records attributed to C J Schwarz.

16 recordsLinked to original sources
PubMed2006

An extension of the Cormack-Jolly-Seber model for continuous covariates with application to Microtus pennsylvanicus.

Recent developments in the Cormack-Jolly-Seber (CJS) model for analyzing capture-recapture data have focused on allowing the capture and survival rates to vary between individuals. Several methods have been developed in which capture and survival are functions of auxiliary variables that may be discrete, constant over time, or apply to the population as a whole, but the problem has not been solved for continuous covariates that vary with both time and individual. This article proposes a new method to handle such covariates by modeling changes over time via a diffusion process and using logistic functions to link the variable to the CJS capture and survival rates. Bayesian methods are used to estimate the model parameters. The method is applied to study the effect of body mass on the survival of the North American meadow vole, Microtus pennsylvanicus.

Animals↗
PubMed2001

Catch estimation in the presence of declining catch rate due to gear saturation.

One strategy for estimating total catch is to employ two separate surveys that independently estimate total fishing effort and catch rate with the estimator for total catch formed by their product. Survey designs for estimating catch rate often involve interviewing the fishermen during their fishing episodes. Such roving designs result in incomplete episode data and characteristically have employed a model in which the catch rate is assumed to be constant over time. This article extends the problem to that of estimating total catch in the presence of a declining catch rate due, e.g., to gear saturation. Using a gill net fishery as an example, a mean-of-ratios type of estimator for the catch rate together with its variance estimator are developed. Their performance is examined using simulations, with special attention given to effects of restrictions on the roving survey window. Finally, data from a Fraser River gill net fishery are used to illustrate the use of the proposed estimator and to compare results with those from an estimator based on a constant catch rate.

Animals↗
PubMed2001

Catch estimation with restricted randomization in the effort survey.

One common method for estimating total catch is to multiply an estimate for CPUE, the catch per unit effort, by an estimate of total effort obtained from an independent second survey. In general, estimating total effort requires that sample times are chosen at random over the full fishing period; however, in practice, this may not always be possible and the usual estimator may be severely biased. Such a restriction in randomization is likely when aircraft are used to make instantaneous counts of fishing activity. This article proposes alternate estimators for use with both access and roving designs in conjunction with effort surveys for which sample times are not random. Ratio type estimators based on activity counts are developed under various scenarios and their performance examined under simulation. In addition, optimizing strategies for use with multiple activity counts are explored. Finally, data from an in-river gill net fishery on the Fraser River is used to illustrate these results.

Animals↗
PubMed2000

Estimation of age-specific breeding probabilities from capture-recapture data.

We provide a new method for estimating the age-specific breeding probabilities from recaptures or resightings of animals marked as young. Our method is more direct than previous methods and allows the modeler to fit and compare models where the age-specific breeding proportions are equal over different cohorts or are a function of external covariates.

Age Factors↗
PubMed1999

The stratified Petersen estimator with a known number of unread tags.

The Petersen estimator estimator of abundance can be biased when the assumption of homogeneous capture probability or homogeneous recapture probability is violated. Often this heterogeneity is related to the time or place of capture or recapture, and if these can be stratified, the stratified Petersen estimator reduces the bias caused by this heterogeneity. In some experiments, not all the recovered tagged animals can be examined, and only a subsample has its stratum of release and recovery determined. We develop methods for this modified experiment and apply them to estimate the number of salmon returning to spawn in a river in British Columbia, Canada.

Animals↗
PubMed1988

Psychiatric short-stay units across Canada.

The limited literature on brief hospitalization programs raised questions about the actual extent of use of this process in Canada. Inquiry was first made to all Health Ministers, University Department Heads and Section Chairmen. A questionnaire was mailed to the hospitals identified and this also requested any supplementary names of units known to the respondents. Initially, 22 hospitals were named as having short-stay units, but eight of these proved not to have one. Basic data on the 14 units actually found is provided. It is suggested that units of this type could be separated into two main groups according to the rate of discharge of patients directly into the community. Those with a high community discharge rate might be called Short-Stay Treatment Units and those with a lower community discharge rate might be known as Assessment Units. The former tend to have fewer admissions per bed, lower occupancy rates, somewhat longer LOS and location in or near the main psychiatric inpatient unit. These factors tend to be reversed in the latter.

Canada↗
PubMed1987

AIDS and marijuana use.

Explore the source record for details and available documents.

Acquired Immunodeficiency Syndrome↗
PubMed1980

Treatment of the elderly on a general hospital psychiatric short-stay unit.

Two out of seven general hospital psychiatric units and the local mental hospital in the Vancouver area set an arbitrary age limit of 65 or 70 on admissions. Administrative reasons given for this include the presumed likelihood of organicity and chronicity, implying difficulties in disposition, and problems in maintaining an active therapeutic milieu with patients of other ages. Data are presented on 40 patients who were over the age of 65 and accounted for 8% of all admissions during 1977 to a Psychiatric Short-Stay Unit in a downtown general hospital. It was found that over three-quarters of the admissions had a primary functional diagnosis, that the mean duration of stay was 5.73 days, that two-thirds of the patients were able to return to their former place of living on discharge and that over one-half of the patients located on follow-up, 18 to 24 months later, were still residing in the same situation. During hospitalization, almost one-half of the patients received no psychotropic prescription and almost one-third, no physical prescription. Some of the psychosocial factors in the treatment program are presented. It is concluded that this preliminary study suggests that the administrative apprehensions in relation to treatment of the elderly in general hospital psychiatric units and mental hospitals can be countered.

Aged↗
PubMed1978

Charging a patient with assault of a nurse on a psychiatric unit.

A patient was successfully charged with assault of a nurse on a Psychiatric Unit and was placed on probation for one year. The judge found her guilty despite the location of the incident and her 20-year history of previous psychiatric treatment, including 14 hospitalizations. Following this confrontation, the patient improved markedly in her behaviour and has continued to lead a more productive life without hysterical outbursts. It is concluded that proceeding with legal charges in such a situation is justifiable and can also be therapeutic.

Adult↗
PubMed1967

A survey of health and psychiatric services on Canadian campuses.

The co-operation of the Canadian Union of Students was readily obtained for a survey of the facilities for health and psychiatric services currently available on Canadian campuses. A 100% response was obtained from the 49 campuses on the original list. Thirty-eight campuses had health services, but the staffing and facilities of these varied widely. Infirmary facilities were provided on 19 campuses. Student use of health services appeared to be heavy where they were provided. Carefully defined psychiatric services were present on 22 campuses, but here again the pattern of staffing varied widely. The percentage of the student body seen by the staff of these psychiatric services ranged from 1.4 to 10.3, with a mean of 2.9%. Only one Canadian university approaches the Recommended Standards of the American College Health Association-one physician and one nurse per 1000 students enrolled. Using the currently available figures on the expected incidence of emotional disturbance among university students and the average duration of psychiatric treatment, it was estimated that a psychiatric service needed .5 team member per 1000 students enrolled. The value of infirmary beds on the campus is also emphasized.

Adult↗