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Biomedical subjects

J Halpern

Publications and source records attributed to J Halpern.

At least 127 records · Page 7Linked to original sources
PubMed1977

Time-related increase in leucocyte yields by continuous-flow centrifugation (CFC) leukopheresis.

Continuous flow centrifugation leukopheresis lasting 3 to 4 h was performed 18 times on 16 normal donors. The total yield of leucocytes collected was 1.59 +/- 0.14 x 10(10) (mean +/- SE). Comparison of leucocyte yields on the first, second, third and fourth hour of leukopheresis indicated a progressive increase with time in 15 out of 18 procedures, with 3.6 times more leucocytes collected within the last hour of leukophoresis as compared to the first hour. This increase was independent of the volume of leucocytes collected per unit time, since an equally significant increase was found when calculated per 100 ml of leucocyte concentrate. Although the mechanism of this improvement in yield with time is unknown, the present data indicate, that moderate prolongation of the duration of leukopheresis may result in an increase in efficiency which is comparable to that produced by the use of hydroxyethyl starch, etiocholanolone or corticosteroids.

Blood Transfusion↗
PubMed1976

Predicting resource utilization in a comprehensive center: an evaluation of three alternative methods.

Three alternative methods for obtaining anticipated resource utilization information for comprehensive mental health centers are proposed. The methods differ on two dimensions, sample selection and statistical technique. Using an admission cohort rather than a discharge cohort and eliminating patients who terminated treatment against medical advice permitted a refined prediction. Although no significant differences were found between the chi-square and multiple-regression techniques, the latter resulted in a substantially greater degree of flexibility.

Humans↗
PubMed1975

Readmission discount factors in program evaluation. An output value analysis of an adult psychiatry program.

The application of output value analysis, a type of benefit/cost analysis, to a psychiatric patient population is reported. A method for discounting the value of the program if a patient was readmitted within a year after discharge was introduced. The application of this discount factor reduces the value produced by the program and thereby reduces both productivity and effectiveness indices. When applied to groups known to differ in readmission rates, such as first admissions and readmissions or voluntary and involuntary admissions, the discount factor can accentuate group differences markedly. When selected diagnostic groups were compared, the discount factor could even reverse the relative standing of the groups.

Brain Damage, Chronic↗
PubMed1975

Prediction of body composition in habitually active middle-aged men.

In 45 physically active men (ages 35-67 yr) who underwent hydrostatic weighing to determine body composition, multiple regression equations were developed for the prediction of body density (D), lean body weight (LBW), fat body weight (FBW), and % fat using selected anthropometric measurements. The prediction accuracy for these parameters using several previously generated anthropometric regression equations was also determined. With equations developed from the present data a substantially higher correlation was obtained between measured and predicted LBW (r = 0.95) than between measured and predicted D (r = 0.85), FBW (r = 0.88), or % fat (r = 0.84). When previously developed equations were applied to the present sample, correlations between measured and predicted values were considerably lower (4-42%) than in the original studies; this reduction was least in the case of LBW. Analysis of previous data indicated that in selected populations total body weight can account for a relatively large fraction of the variance in LBW. LBW may be estimated quite accurately (r greater than or equal to 0.90) in physically active men with one of several regression equations which include total body weight as an independent variable.

Adult↗
PubMedDate not supplied

Multi-stage sampling in genetic epidemiology.

When data are expensive to collect, it can be cost-efficient to sample in two or more stages. In the first stage a simple random sample is drawn and then stratified according to some easily measured attribute. In each subsequent stage a random subset of previously selected units is sampled for more detailed observation, with a unit's sampling probability determined by its attributes as observed in the previous stages. These designs are useful in many medical studies; here we use them in genetic epidemiology. Two genetic studies illustrate the strengths and limitations of the approach. The first study evaluates nuclear and mitochondrial DNA in U.S. blacks. The goal is to estimate the relative contributions of white male genes and white female genes to the gene pool of African-Americans. This example shows that the Horvitz-Thompson estimators proposed for multi-stage designs can be inefficient, particularly when used with unnecessary stratification. The second example is a multi-stage study of familial prostate cancer. The goal is to gather pedigrees, blood samples and archived tissue for segregation and linkage analysis of familial prostate cancer data by first obtaining crude family data from prostate cancer cases and cancer-free controls. This second example shows the gains in efficiency from multi-stage sampling when the individual likelihood or quasilikelihood scores vary substantially across strata.

Black or African American↗
PubMedDate not supplied

Sequential treatment allocation procedures in clinical trials--with particular attention to the analysis of results for the biased coin design.

We discuss the advantages and problems of using sequential allocation procedures for assigning treatments in a clinical trial. We use Monte Carlo methods to study the exact distribution of the fourfold chi-squared statistic for the case of no stratifying variables except sequence of entry. We display situations in which the distribution is well-approximated by the chi-squared distribution or by Efron's adjusted chi-squared and situations where these approximations fail. We provide suggestions for recognition and handling of situations in which both approaches fail.

Clinical Trials as Topic↗
PubMedDate not supplied

Medical data-bases-telecommunications issues in the 1980s.

This paper gives a brief description of the telecommunications problems encountered when accessing medical data-bases. In the first part of the article, the authors described how the creation of a special telecommunications working group at IMA (the French MEDLINE Centre) helped to handle and solve these problems. The second part shows how French users will be able to access new European data-bases; and discusses the changes brought about by the development of networks such as TRANSPAC and EURONET. It also compares the communications costs for all access configurations.

France↗