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Biomedical subjects

R J Little

Publications and source records attributed to R J Little.

27 records · Page 2Linked to original sources
PubMed1988

Some statistical analysis issues at the World Fertility Survey.

"The World Fertility Survey carried out cross-sectional probability surveys of fertility in more than 40 developing countries between 1972 and 1984. Statistical issues in regression analysis of the data are reviewed, including treatment of interactions, the selection of regressor variables, and appropriate linear models for rate variables. Similar issues arise in many other applications of regression to observational data."

Birth Rate↗
PubMed1987

Peritoneal kinetics in children undergoing continuous ambulatory/cycling peritoneal dialysis.

We present a report on peritoneal kinetics in children undergoing continuous ambulatory/cycling peritoneal dialysis (CAPD/CCPD). The effect of long-term treatment with CAPD/CCPD, peritonitis episodes, and dialysate inflow volume on peritoneal kinetics in children was evaluated. Peritoneal kinetic studies (PKSs) were performed in 47 pediatric patients at different times following initiation of CAPD/CCPD. In 18 of these patients, PKSs were repeated up to four times with an unchanged dialysate inflow volume after up to 55 months of CAPD/CCPD treatment. The PKS consisted of a 120-minute dwell with a 1.5% dextrose dialysate solution. Peritoneal clearance, dialysance, and dialysate to plasma (D/P) concentration ratios were calculated after 30, 60, and 120 minutes. The results of the serial PKSs demonstrate stable peritoneal creatinine and urea-N clearance, dialysance or D/P concentration ratios. Furthermore, there was no adverse effect of 32 peritonitis episodes. Finally, inflow volumes correlated directly with clearances of creatinine (P less than .01), urea-N (P less than .001), and potassium (P less than .001), and there was an inverse relationship to the D/P concentration ratios of creatinine (P less than .01), urea-N (P less than .01), potassium (P less than .01), and uric acid (P less than .01). Thus, CAPD/CCPD is a useful and effective long-term treatment modality for pediatric patients. Maximal dialysate inflow volumes should be provided to enhance peritoneal kinetics.

Adolescent↗
PubMed1982

The statistical analysis of low-level radioactivity in the presence of background counts.

The analysis of low-level or background dominant radioactivity is complicated by the fact that sample net rate of activity above background may be negative, because of random fluctuations. The traditional large sample confidence intervals can contain negative values for the net rate, although we know the net rate is positive. This problem leads to statistically unsound practices such as the reporting of "less than" values when the net value lies below a certain "detectable limit". In this paper we present two Bayesian analyses of the data which take account of the fact that the net rate is positive, and thus always lead to positive estimates and probability intervals for the true underlying rate. The estimates and intervals are compared with classical results for twenty trial data sets.

Background Radiation↗
PubMedDate not supplied

On summary measures analysis of the linear mixed effects model for repeated measures when data are not missing completely at random.

Subjects often drop out of longitudinal studies prematurely, yielding unbalanced data with unequal numbers of measures for each subject. A simple and convenient approach to analysis is to develop summary measures for each individual and then regress the summary measures on between-subject covariates. We examine properties of this approach in the context of the linear mixed effects model when the data are not missing completely at random, in the sense that drop-out depends on the values of the repeated measures after conditioning on fixed covariates. The approach is compared with likelihood-based approaches that model the vector of repeated measures for each individual. Methods are compared by simulation for the case where repeated measures over time are linear and can be summarized by a slope and intercept for each individual. Our simulations suggest that summary measures analysis based on the slopes alone is comparable to full maximum likelihood when the data are missing completely at random but is markedly inferior when the data are not missing completely at random. Analysis discarding the incomplete cases is even worse, with large biases and very poor confidence coverage.

Computer Simulation↗
PubMedDate not supplied

Balanced centralized and distributed database design in a clinical research environment.

Clinical research databases can meet both research and clinical needs, but this ideal is seldom achieved. Priorities often differ for those who collect and ultimately use the data and those who develop data systems. Traditional database designs also create logistical barriers that hamper communication. The Michigan Alzheimer's Disease Research Center has developed a secure, distributed data system with centralized data entry that provides an intuitive, individually customized interface for investigators in their clinics, laboratories and offices. Data are kept in a form that can be readily understood without reference to a code-book. Investigators can modify and query their own copies of the database without knowledge of programming languages. Balancing centralized and distributed designs for research databases enhance the accuracy and completeness of data collection and increases the use of data for research and clinical care.

Aged↗
PubMedDate not supplied

Results of new air caloric testing method among normal subjects. II. Monophasic testing.

A new caloric irrigation method is described. In the new method, the temperature of a continuous aural irrigation is switched between hot and cold values at precisely specified times. The durations of hot and cold pulses have been calculated to produce specific caloric stimulation intensities based on known heat transmission characteristics of the labyrinth area. A brief "washout" irrigation is used to eliminate promptly all caloric stimulation effects at the conclusion of each test. The present study concentrated upon the question of how long the "washout" pulse should be in order to obtain optimum results. Repetitive application of a uniform stimulus intensity to 6 normal subjects indicated that short inter-test intervals can be used without causing vestibular habituation. Prompt removal of the caloric stimulus can be accomplished by proper timing the "washout" phase of the new technique.

Caloric Tests↗