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Biomedical subjects

W P Dunlap

Publications and source records attributed to W P Dunlap.

At least 19 recordsLinked to original sources
PubMed2000

Canonical correlation and chi-square: relationships and interpretation.

A 2 x 2 chi-square can be computed from a phi coefficient, which is the Pearson correlation between two binomial variables. Similarly, chi-square for larger contingency tables can be computed from canonical correlation coefficients. The authors address the following series of issues involving this relationship: (a) how to represent a contingency table in terms of a correlation matrix involving r - 1 row and c - 1 column dummy predictors; (b) how to compute chi-square from canonical correlations solved from this matrix; (c) how to compute loadings for the omitted row and column variables; and (d) the possible interpretive advantage of describing canonical relationships that comprise chi-square, together with some examples. The proposed procedures integrate chi-square analysis of contingency tables with general correlational theory and serve as an introduction to some recent methods of analysis more widely known by sociologists.

Chi-Square Distribution↗
PubMed2000

Determining the number of factors to retain: a Windows-based FORTRAN-IMSL program for parallel analysis.

Parallel analysis (PA; Horn, 1965) is a technique for determining the number of factors to retain in exploratory factor analysis that has been shown to be superior to more widely known methods (Zwick & Velicer, 1986). Despite its merits, PA is not widely used in the psychological literature, probably because the method is unfamiliar and because modern, Windows-compatible software to perform PA is unavailable. We provide a FORTRAN-IMSL program for PA that runs on a PC under Windows; it is interactive and designed to suit the range of problems encountered in most psychological research. Furthermore, we provide sample output from the PA program in the form of tabled values that can be used to verify the program operation; or, they can be used either directly or with interpolation to meet specific needs of the researcher.

Factor Analysis, Statistical↗
PubMed1999

A program to compute McGraw and Wong's common language effect size indicator.

McGraw and Wong (1992) have described a very appealing index of effect size that requires no prior knowledge of statistics to understand, which they termed CL, the common language effect size indicator. CL is the probability that a score randomly sampled from one distribution will be larger than a randomly sampled score from a second distribution. McGraw and Wong describe how to compute CL from the means and standard deviations of two groups, using tables of normal curve probability values. The program described herein computes CL without lookup tables but also permits the user to compute CL from Cohen's d, from a t test for independent groups, or from point-biserial r, the correlation between a dichotomous and a continuous variable. A table giving CL for various values of d is also provided, as are the equations for converting t and r to d.

Models, Statistical↗
PubMed1997

Sociodemographic risk factors to disease control in children with diabetes.

This study examined the effects of sociodemographic variables such as ethnicity, socioeconomic status (SES), and family structure on disease control in 58 children with diabetes stratified by ethnicity and SES. Three dependent variables were chosen to evaluate the disease control of the study participants, including HbA1 values averaged over the year prior to study participation, number of hospitalizations, and number of hypoglycaemic blackouts. SES and family structure, but not ethnicity, were the primary risk factors to disease control. Children from low SES families were in poorer glycaemic control (mean HbA1 = 12.6%) and experienced more episodes of hypoglycaemia-related loss of consciousness (mean = 0.5 per patient) than did children from middle income families (mean HbA1 = 10.4%; mean blackouts = 0.1 per patient). In addition, children from middle-class, two-parent families were in better metabolic control than all other groups. These results indicate that it may not be ethnicity per se, but other factors that often covary with ethnic status, that may pose a risk to the disease status of children and adolescents with diabetes.

Adolescent↗
PubMed1995

Effects of relative area on matching heterochromatic stimuli for saturation.

Participants adjusted the saturation of one rectangular color stimulus so that it appeared to match the saturation of another rectangular color stimulus for stimulus pairs of different relative areas. In Experiment 1, in which stimuli of complementary colors were used, higher saturation stimuli were consistently chosen for large areas to match lower saturation stimuli in smaller areas. In Experiment 2, better saturation matches were obtained if participants fixated and the stimuli were presented for very brief durations. In Experiment 3, larger color contrast effects were obtained with hue pairs that were nearer to complementary than with hue pairs that were more nearly the same. These findings agree with the interpretation that biases in relative saturation selected to match stimuli of different relative size are largely the result of negative afterimages of the larger stimulus having greater impact on the apparent saturation of the smaller stimulus.

Afterimage↗
PubMed1995

Family environment and the interrelation of family structure, child behavior, and metabolic control for children with diabetes.

Examined perceptions of the family environment in a cross-regional sample of 90 families who had children with diabetes and 89 controls. Families were classified as either traditional (intact) or nontraditional (single-parent or blended families). Parents of children with diabetes reported less family expressiveness, which was a predictor of clinically higher levels of child behavior problems than controls. Parents in nontraditional families reported lower levels of organization, less emphasis on active-recreational pursuits, and more child behavior problems than traditional families. An additive effect of diabetes and nontraditional family structure was found for children with diabetes from nontraditional families, who reported substantially less cohesion than all other groups. Nontraditional family structure was more disruptive for children with diabetes than for controls; it was the best predictor of behavior problems and was related to poorer metabolic control.

Adolescent↗
PubMed1994

Indexing cognitive tests to alcohol dosage and comparison to standardized field sobriety tests.

Cognitive tests from a computerized battery of mental tests and standardized roadside field sobriety tests (FST) were administered in three experiments involving graded dosages of alcohol but different administration schedules. In the first experiment, subjects were raised to one of four levels of alcohol dosage in four sessions 1 week apart. In the second experiment, the descending branch of the blood alcohol concentration (BAC) curve was monitored from 150 mg/dl BAC in a single session. In the third experiment, the ascending and descending limbs of the alcohol dosage curve were followed over a single session. Dose response relationships were observed for all tests, and the changes were statistically significant (p < .001) in all three studies for all tests when evaluated singly, except for grammatical reasoning. When cognitive and FST tests were combined into a single multiple regression analysis, Gaze Nystagmus consistently accounted for the most variance in BAC, followed by code substitution. While multiple regression analyses reveal that tests from the two batteries can be combined to improve overall prediction of alcohol concentration, it is also true that the two batteries share considerable variance (i.e., > 30%). This suggests that, while the two batteries may not be substitutable, they are measuring different aspects of the same thing.

Adult↗
PubMed1993

Selective vulnerability and early progression of hippocampal CA1 pyramidal cell degeneration and GFAP-positive astrocyte reactivity in the rat four-vessel occlusion model of transient global ischemia.

Selective, delayed-onset vulnerability of hippocampal CA1 pyramidal cells has been reported as a unique phenomenon in man and the rat four-vessel occlusion (4-VO) model of global ischemia. This has become of great interest for clarification of CA1 pathophysiology and pharmacological intervention after global ischemia. Studies of pathophysiology and pharmacotherapy appear to be impeded by variability in specific criteria and duration of 4-VO ischemia for producing selective CA1 and differential CA1-CA3 damage. The goals of this study were to: (1) develop specific criteria for 4-VO ischemia to ensure selective, bilaterally symmetrical CA1 pyramidal cell damage, (2) examine the effects of 15 min of ischemia on concomitant CA1 cell necrosis and presence of remaining and/or "viable" neurons postischemia, (3) compare 15 and 30 min of ischemia on differential vulnerability of CA1-CA3 subfields, and (4) evaluate the effects of 15 min of ischemia on CA1 pyramidal cell necrosis and glial fibrillary acidic protein (GFAP)-positive astrocyte reactivity in CA1. After 15 min of ischemia, hippocampal pyramidal cell damage was well delineated, with CA1 severely damaged, but leaving CA3 virtually intact. In contrast, 30 min of ischemia produced severe CA1 and less severe CA3 necrosis. Histological evaluations across Days 1, 3, 6, and 14 indicated a significant delayed onset of CA1-CA3 cell necrosis by Day 3. Counting of remaining cells indicated a detectable loss of some large pyramidal neurons even 1 day after ischemia. Compared to controls, there was a differential increase in GFAP-positive astrocytes in CA1-CA3 after ischemia. The results provided quantitative data on the effects of specific 4-VO criteria and durations on: (1) selective CA1 cell necrosis, (2) differential CA1-CA3 cell vulnerability, (3) presence of postischemic remaining and/or viable neurons, and (4) prospect of a "therapeutic window" for pharmacological treatment of CA1 neuronal injury.

Animals↗
PubMed1993

Effects of graded dosages of alcohol on nine computerized repeated-measures tests.

We report a controlled laboratory validation experiment to provide an empirical sequel to the general background of the development of the Automated Performance Test System (APTS) that was presented in Turnage et al. (1992). The purpose of this study was to index performance deficit against various Blood Alcohol Concentrations (BACs) of small (0.05% BAC), medium (0.10% BAC), and large (0.15% BAC) dosages as well as a placebo (0.00 BAC) condition. Blood alcohol concentrations, measured in four different ways, were highly reliable and the method with the highest intercorrelation was whole blood. When taken singly, eight of the nine tests produced significant (p < 0.001) relationships with the disparate blood alcohol levels, which were essentially monotonic. A multiple regression analysis suggested that most of the tests were behaving similarly and that two or three tests accounted for 52 to 54% of the variance attributable to alcohol that was explained by the longer battery. While all tests appear valid, some of them appeared more sensitive than others (viz., code substitution, manikin, and choice reaction time). From the standpoint of these tests, greater changes occurred in cognitive function between the placebo and 0.05 level than between the 0.05 and 0.10 levels. However, the greatest reduction in performance occurred between 0.10 and 0.15, and the relatively abrupt nature of this change implies that sharp decrements in cognitive performance occur at that point. There were individual differences in resistance to alcohol, and there is strong inference that these differences would be reliable if they were tested again. We believe that further development and study of such techniques is warranted for use in fitness-for-duty testing and development of a dose equivalency index.

Adult↗
PubMed1993

Postpubertal disease status in diabetes and factor structure anomaly on the WISC-R.

Diabetic children have been found to display an anomalous factor structure on the Wechsler Intelligence Scale for Children-Revised (WISC-R) (Holmes, Cornwell, Dunlap, Chen, & Lee, 1992). The present study sought to extend this finding with a larger cross-regional sample of children to determine which, if any, demographic or disease factor(s) might be related to the anomalous structure. Results revealed that groups of older (> = 12 years) children and those with late disease onset (> = 5 years) exhibited an anomalous four-factor structure in which the traditional Perceptual Organization factor (II) split into two factors: Picture Completion and Picture Arrangement formed a visual discrimination factor; and Block Design and Object Assembly created a spatial conceptual factor. It is postulated that diabetic performance on this visual discrimination factor may reflect mild visual neuropathies, often associated with adolescence and postpubertal disease status.

Adolescent↗
PubMed1993

Relating alcohol-induced performance deficits to mental capacity: a suggested methodology.

Performance tests are generally more reliable and more easily administered than on-the-job measures of performance, and in this way are preferable for studying the adverse consequences of environmental stressors. However, a linkage or context would be useful in interpretation of these laboratory measures. This paper reports findings with two indexing methods using multiple regression. In the first study, we illustrate "dose equivalency" where deficits on microcomputer performance tests were related to graded dosages of alcohol, and prediction equations of blood alcohol level were established. In the second experiment, "surrogate criteria" are demonstrated where cognitive mental tests of military aptitude, known to be predictive of operational performances, were administered to a sample who were tested repeatedly on the same microcomputer performance test. Multiple regression analyses of the computerized tests with the amplitude tests were significant (p < 0.01) and ranged from R = 0.50 to 0.94. Finally, the loss in performance owing to alcohol was indexed to loss on the microcomputer tests through the relationship of the tests to the Armed Services Vocational Aptitude Battery (ASVAB). Since the latter is strongly predictive of all forms of military operational performance, we suggest that alcohol-related losses in microcomputer performance test scores can serve as a useful intermediary, permitting meaningful linkage to these real-world performances.

Adult↗
PubMed1992

Gender differences in the learning status of diabetic children.

The learning status of 95 diabetic boys and girls and 97 matched controls was evaluated using the Wechsler Intelligence Scale for Children--Revised IQ factors and school histories. Of interest was whether diabetic boys would evidence more learning difficulties. Results indicated that diabetic boys had significantly lower Freedom From Distractibility scores compared with scores of diabetic girls and control Ss and lower Perceptual Organization scores compared with scores of control boys. Although group scores were still within the average range of functioning, a significantly high percentage of diabetic boys (40%) compared with diabetic girls (16%) had learning problems that warranted either special instructional services or grade retention. Diabetic children experienced more learning difficulties (24%) than controls (13%), supporting research findings that diabetes is associated with increased risk of learning problems.

Adolescent↗
PubMed1992

Loss of hippocampal CA1 pyramidal neurons correlates with memory impairment in rats with ischemic or neurotoxin lesions.

Rats were trained for 20 days in a modified T maze to perform an invariant, tactile discrimination and a variable, delayed spatial discrimination, and then were exposed either to 30 min of transient forebrain ischemia or to low- or high-dose ibotenic acid to damage the dorsal hippocampus bilaterally. Only rats exposed to ischemia or high-dose ibotenic acid demonstrated impaired performance during 30 postoperative test days on both aspects of the task (p less than .05). Volume of hippocampal damage did not predict performance. However, the extent of CA1 pyramidal neuron loss correlated significantly with performance on the delayed spatial discrimination (p less than .01). Damage to the dentate gyrus and CA2-3 did not correlate with performance. These results support the view that the hippocampus, in particular the CA1 region, is crucial for certain types of memory performance.

Animals↗
PubMed1991

Communality of videogame performances with tracking tasks.

Performances on three videogames were compared with two different tracking tasks and a third dual tracking task, after stability of performance was achieved by 40 male subjects. The six tasks were performed in succession for three weeks each, and one year separated administration of the tracking tasks from the videogames. Convergence of the cross-correlations among these tasks occurred such that higher correlations were attained for scores obtained late in practice (late/late) of two tasks (even when they were performed a year apart) rather than for scores obtained earlier in training (viz., early/early). High communality between these two types of tasks was observed as indicated by virtual overlap between the videogames and the tracking tasks, even though different control media (joysticks, knobs), control orders (zero/first), and control inputs (displacement/force transducer) were required. Because these tasks apparently index similar abilities, there may be advantages to measuring tracking skills with videogames, which include low cost, wide availability, inherent interest to subjects and motivation, rapid approach to stable levels, and, in many cases greater apparent face validity relative to real world performance requirements.

Adult↗
PubMed1990

Eye movement indices of mental workload.

Four investigations were carried out to assess the feasibility of using eye movement measures as indices of mental workload. In the first experiment, saccadic extent was measured during free viewing while subjects performed low, moderate and high complexity, auditory tone counting as the workload tasks. The range of saccadic extent decreased significantly as tone counting complexity (workload) was increased. In the second experiment the range of spontaneous saccades was measured under three levels of counting complexity with a visual task that did not require fixation or tracking. The results indicated that the extent of saccadic eye movements was significantly restricted as counting complexity increased. In the third experiment, the effects of practice were examined and decreased saccadic range under high tone counting complexity was observed even when significant increases in performance occurred with practice. Finally, in experiment 4, the first experiment was repeated with additional optokinetic stimulation and the saccadic range was again observed to decrease with tone counting complexity. The results indicated that the extent of spontaneous and elicited eye movements was significantly restricted as counting complexity increased. We conclude that this measure may provide a valuable index of mental workload.

Adult↗
PubMed1990

Effects of uric acid and caffeine on A1 adenosine receptor binding in developing rat brain.

Previous studies have demonstrated that elevated levels of serum uric acid or caffeine are associated with increased locomotor activity in rats and humans. Since uric acid and caffeine are structurally similar, it was hypothesized that these compounds alter locomotor activity through a common neural mechanism, specifically by acting as receptor antagonists at adenosine A1 binding sites. In vitro competition of caffeine and uric acid against the A1 agonist, [3H] cyclohexyladenosine ([3H]CHA), was conducted using homogenates of adult rat forebrain. Caffeine effectively competed for the A1 binding site as previously reported (IC50 = 107 microM), but uric acid failed to compete with [3H]CHA binding at concentrations within a relevant physiological range. Nevertheless, in vivo experiments indicated that chronic elevation of uric acid following allantoxanamide treatment of male rats on days 4-27 of life significantly decreased A1 receptor binding in the striatum, a region traditionally implicated in mammalian locomotion. In contrast, chronic caffeine treatment on days 4-27 of life caused an increase in A1 receptor binding in the cortex similar to increases reported previously in whole brain. These changes in A1 receptor binding following chronic elevation of uric acid or caffeine did not persist in rats that had been withdrawn from allantoxanamide or caffeine treatment for 14 days. Results from in vitro and in vivo experiments indicate that despite a similar molecular structure uric acid does not act by the same mechanism as caffeine to increase locomotor activity in rats.

Adenosine↗
PubMed1990

Assessment of the Vistech contrast sensitivity test for repeated-measures applications.

Contrast sensitivity using Vistech plates was measured repeatedly in normal subjects to determine predictive power. The contrast sensitivity measures were quite stable from the first administration, and practice effects were not observed. Test-retest reliability was lowest for the lower spatial frequencies, but was adequate throughout if more than one measurement was made. Threshold scores for all five spatial frequencies were generally not independent and factor analysis revealed that only two spatial frequency domains were relatively independent: high and low. The correlations between adjacent spatial frequencies were highest, and correlations decreased as distance between spatial frequencies increased. To detect subtle differences all three Vistech plates should be used to arrive at a threshold for each spatial frequency and, if time permits, more measures should be taken at the lower spatial frequencies to compensate for the lower reliability. This method is believed to be adequate for repeated-measures clinical and experimental studies.

Adult↗