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PubMed1992

Parents and AIDS education.

The objective of this research was to study parents' attitudes toward AIDS education in schools. Questionnaires were mailed to employees in an industrial plant and a hospital in a city of 150,000 in Ontario, Canada. Two hundred and sixteen questionnaires from parents with children in schools were analyzed. Two thirds of the parents agreed that AIDS education should discourage premarital sex; whereas, 88% believed that AIDS education should teach about condoms. Pearson correlations and multiple regression were used to analyze hypotheses that tested attitudes toward AIDS education in the schools. Two predictor variables--attitude toward premarital intercourse and fear of casual contact of AIDS--were significantly correlated with all three measures of attitudes toward AIDS education in the schools. Church attendance and knowledge of AIDS were related to both attitudes toward discouraging premarital sex and teaching about condoms. Three multiple regression models were constructed to predict attitudes toward AIDS education in the schools. The final models accounted for between 11% and 33% of the variance.

Acquired Immunodeficiency Syndrome↗
PubMed2000

Placebo-controlled trial of indole-3-carbinol in the treatment of CIN.

OBJECTIVE: Most precancerous lesions of the cervix are treated with surgery or ablative therapy. Chemoprevention, using natural and synthetic compounds, may intervene in the early precancerous stages of carcinogenesis and prevent the development of invasive disease. Our trial used indole-3-carbinol (I-3-C) administered orally to treat women with CIN as a therapeutic for cervical CIN. METHODS: Thirty patients with biopsy proven CIN II-III were randomized to receive placebo or 200, or 400 mg/day I-3-C administered orally for 12 weeks. If persistent CIN was diagnosed by cervical biopsy at the end of the trial, loop electrocautery excision procedure of the transformation zone was performed. HPV status was assessed in all patients. RESULTS: None (0 of 10) of the patients in the placebo group had complete regression of CIN. In contrast 4 of 8 patients in the 200 mg/day arm and 4 of 9 patients in the 400 mg/day arm had complete regression based on their 12-week biopsy. This protective effect of I-3-C is shown by a relative risk (RR) of 0.50 ((95% CI, 0. 25 to 0.99) P = 0.023) for the 200 mg/day group and a RR of 0.55 ((95% CI, 0.31 to 0.99) P = 0.032) for the 400 mg/day group. HPV was detected in 7 of 10 placebo patients, in 7 of 8 in the 200 mg/day group, and in 8 of 9 in the 400 mg/day group. CONCLUSIONS: There was a statistically significant regression of CIN in patients treated with I-3-C orally compared with placebo. The 2/16 alpha-hydroxyestrone ratio changed in a dose-dependent fashion.

Administration, Oral↗
PubMed1990

Regression analyses of repeated measures data in cognitive research.

Repeated measures designs involving nonorthogonal variables are being used with increasing frequency in cognitive psychology. Researchers usually analyze the data from such designs inappropriately, probably because the designs are not discussed in standard textbooks on regression. Two commonly used approaches to analyzing repeated measures designs are considered in this article. It is argued that both approaches use inappropriate error terms for testing the effects of independent variables. A more appropriate analysis is presented, and two alternative computational procedures for the analysis are illustrated.

Cognition↗
PubMed2003

Assessment of homogeneity vs. heterogeneity of residual variance in random regression test-day models in a Bayesian analysis.

Test-day first-lactation milk yields from Holstein cows were analyzed with a set of random regression models based on Legendre polynomials of varying order on additive genetic and permanent environmental effects. Homogeneity and heterogeneity of residual variance, assuming three and 30 arbitrary measurement error classes of different length were considered. Unknown parameters were estimated within a Bayesian framework. Bayes factors and a checking function for the cross-validation predictive densities of the data were the tools chosen for selecting among competing models. Residual variances obtained from 30 arbitrary intervals were nearly constant between d 70 and 300 and tended to increase towards the extremes of the lactation, especially at the onset. In early lactation, the temporary measurement errors were found to be larger and highly variable. A high order of the regression submodels employed for modeling the permanent environmental deviations tended to strongly correct the heterogeneity of the residual variance. Accordingly, the assumption of homogeneity of residual variance was the most plausible specification under both comparison criteria when the number of random regression coefficients was set to five. Otherwise, the heterogeneity assumption, using three or 30 error classes, was better supported, depending on the criterion and on the order of the submodel fitted for the permanent environmental effect.

Analysis of Variance↗
PubMed2002

Effect of iron supplementation on incidence of infectious illness in children: systematic review.

OBJECTIVE: To evaluate the effect of iron supplementation on the incidence of infections in children. DESIGN: Systematic review of randomised controlled trials. DATA SOURCES: 28 randomised controlled trials (six unpublished and 22 published) on 7892 children. INTERVENTIONS: Oral or parenteral iron supplementation or fortified formula milk or cereals. OUTCOMES: Incidence of all recorded infectious illnesses, and individual illnesses, including respiratory tract infection, diarrhoea, malaria, other infections, and prevalence of positive smear results for malaria. RESULTS: The pooled estimate (random effects model) of the incidence rate ratio (iron v placebo) was 1.02 (95% confidence interval 0.96 to 1.08, P=0.54; P<0.0001 for heterogeneity). The incidence rate difference (iron minus placebo) for all recorded illnesses was 0.06 episodes/child year (-0.06 to 0.18, P=0.34; P<0.0001 for heterogeneity). However, there was an increase in the risk of developing diarrhoea (incidence rate ratio 1.11, 1.01 to 1.23, P=0.04), but this would not have an overall important on public health (incidence rate difference 0.05 episodes/child year, -0.03 to 0.13; P=0.21). The occurrence of other illnesses and positive results on malaria smears (adjusted for positive smears at baseline) were not significantly affected by iron administration. On meta-regression, the statistical heterogeneity could not be explained by the variables studied. CONCLUSION: Iron supplementation has no apparent harmful effect on the overall incidence of infectious illnesses in children, though it slightly increases the risk of developing diarrhoea.

Anemia, Iron-Deficiency↗
PubMed1975

A method of structure-activity correlation using Wiswesser Line Notation.

Fragment sets generated manually from Wiswesser Line Notation have been used to correlate the chemical structures of a group of 79 penicillins with their serum binding activity, using multiple regression analysis. Statistically significant correlations were found, with results in accordance with the generally accepted nature of the binding. Algorithmic methods for the generation of such fragment sets are proposed and the use of various structural representations for structure-property correlation within chemical information systems is discussed.

Blood Proteins↗
PubMed1992

Mixed-effects nonlinear regression for unbalanced repeated measures.

Repeated measures data, such as clinical pharmacokinetic data, growth data, and dose-response data, are often inherently nonlinear with respect to a given response function and are frequently incomplete and/or unbalanced. Nonlinear random-effects models together with a variety of estimation procedures have been proposed for the analysis of such data. This paper is concerned with a straightforward procedure for estimating and comparing the parameters of a generalized mixed-effects nonlinear regression model. The asymptotic properties of the proposed estimators are given and large-sample tests of hypothesis provided. The results are applied to in vitro data on the water transport kinetics of hemodialyzers used in the treatment of patients with chronic renal failure.

Biological Transport, Active↗
PubMed2000

The relationship between clinical and kinematic responses from human subject testing in rear-end automobile collisions.

Recent experiments have produced a linked data set of clinical and kinematic responses for human subjects exposed to controlled low-speed rear-end collisions. The purpose of this paper was to examine this paired data set and determine whether the presence or absence of clinical symptoms could be predicted from the peak linear and angular kinematic response of the head and neck. The data were generated using 42 male and female human subjects seated normally in the front passenger seat of a stationary vehicle struck from behind to produce vehicle speed changes of 4 and 8 km/h. Pre- and post-test clinical examinations documented the presence, severity and duration of whiplash-associated disorders (WAD). Logistic regression and backward elimination of independent variables were used to develop the prediction model. The analysis yielded a 16 parameter model that was significantly related (odds ratio = 21.2; P = 0.0069) to the presence or absence of transient whiplash symptoms. The model correctly predicted symptom presence in 13 of 23 tests (sensitivity 57%) and symptom absence in 49 of 52 tests (specificity 94%) in a population of 75 with a symptom prevalence of 31%. The model's positive predictive value was 81% and its negative predictive value was 83%. Despite statistical significance, the model did not discriminate between the presence and absence of symptoms in all tests, and indicated that factors other than the selected peak kinematic responses influenced symptom production.

Accidents, Traffic↗
PubMed1990

Health and the allocation of public expenditures.

In a cross-country study we use a multiple regression in order to estimate the contribution of several factors to life expectancy. We find schooling as the main variable. Medicine also has a significant contribution. Calorie supply has a positive contribution only in the less developed countries.

Cost-Benefit Analysis↗
PubMed2003

Latent transition regression for mixed outcomes.

Health status is a complex outcome, often characterized by multiple measures. When assessing changes in health status over time, multiple measures are typically collected longitudinally. Analytic challenges posed by these multivariate longitudinal data are further complicated when the outcomes are combinations of continuous, categorical, and count data. To address these challenges, we propose a fully Bayesian latent transition regression approach for jointly analyzing a mixture of longitudinal outcomes from any distribution. Health status is assumed to be a categorical latent variable, and the multiple outcomes are treated as surrogate measures of the latent health state, observed with error. Using this approach, both baseline latent health state prevalences and the probabilities of transitioning between the health states over time are modeled as functions of covariates. The observed outcomes are related to the latent health states through regression models that include subject-specific effects to account for residual correlation among repeated measures over time, and covariate effects to account for differential measurement of the latent health states. We illustrate our approach with data from a longitudinal study of back pain.

Back Pain↗
PubMed2003

Genome-wide linkage analysis of systolic blood pressure: a comparison of two approaches to phenotype definition.

Problem 1 of the Genetic Analysis Workshop 13(GAW13) contains longitudinal data of cardiovascular measurements from 330 pedigrees. The longitudinal data complicates the phenotype definition because multiple measurements are taken on each individual. To address this complication, we propose an approach that uses generalized estimating equations to obtain residuals for each time point for each person. The mean residual is then taken as the new phenotype with which to use in a variance components linkage analysis. We compare our phenotype definition approach to an approach that first reduces the multiple measurements to a single measurement and then models these summary statistics as regression terms in a variance components analysis. For each approach, multipoint linkage analysis was performed using the residuals and the SOLAR computer program. Our results show little difference between the methods based on the LOD scores.

Adult Children↗
PubMed1991

Methods of adjustment for estimating the attributable risk in case-control studies: a review.

In the 1980's, progress was made in adjusting estimates of the attributable risk (AR) for confounding factors and in calculating associated confidence intervals. In this paper, methods of adjustment for estimation of the AR in case-control studies are reviewed. The limitations and problems associated with two methods based on stratification, the weighted-sum approach and the Mantel-Haenszel approach, are discussed. They include small-sample bias with the weighted-sum approach and the difficulty of taking interaction into account with the Mantel-Haenszel approach. A third method based on logistic regression is reviewed. It is argued that this latter method has the greatest generality and flexibility, and includes the two other approaches as special cases. Throughout the paper, an example of a case-control study of oesophageal cancer illustrates the use of the methods described.

Alcohol Drinking↗
PubMed1992

Two methods for assessing the risk-factor composition of the HIV-1 epidemic in heterosexual women: southeast England, 1988-1991.

OBJECTIVE: The prevalence of HIV-1 in the heterosexual population in southeast England between 1988 and 1991 was examined using two methods. DESIGN AND METHODS: First, district neonatal seroprevalence was compared on a geographical basis to social and demographic variables reflecting risk-factor prevalence. Second, over the same period eight children who developed AIDS within the first 12 months of life were born. RESULTS: The differences in seroprevalence between districts could be explained by the proportion of livebirths to women born in parts of Africa. An estimated 92% of neonatal seropositives could be associated with this demographic variable. The proportions of livebirths to women born in other countries, the prevalence of notified injecting drug use, and area measures of social deprivation, were only poorly related to HIV seroprevalence, and had no additional explanatory value. Seven of the eight (87.5%) children who developed AIDS in the first year were born to black women from Africa. CONCLUSIONS: Both methods suggest that a high proportion of heterosexually transmitted HIV in southeast England has been imported.

Adult↗
PubMed1998

Severity variations within DRGs: measurement of hospital effects by use of data on significant secondary diagnoses and procedures.

The Diagnosis Related Group classification has provided an excellent basis for enhancing the equity of resource allocation between public acute hospitals. However, it underestimates the higher levels of severity and consequent costliness of referral hospitals. This paper describes a practical way of measuring within-DRG variations in severity, which can be used to increase the precision of casemix-based funding. It involves the regression of length of stay against the numbers of significant diagnoses and procedures, and bence the prediction of additional justified costs. An example is given of its application to data from South Australian public hospitals.

Diagnosis-Related Groups↗
PubMed1992

Utilization review savings at the micro level.

Utilization review (UR) programs have become an integral part of efforts to contain health care costs for private health insurers, employers, and health care organizations. While some studies have measured the overall performance of these programs, important information in the prior level of the health care utilization has not been used in estimating the effectiveness of the program for micro units (e.g., employer groups). In this article, the authors present a model to determine how the impact of the hospital UR program on health care utilization for specific groups varies with historical use patterns. The estimation approach used in this article can be used to determine the effect of UR for specific employer groups without having to rely on the average effectiveness measures for all. Claims obtained from Aetna Health Plans provided data for more than 5,300 employer accounts covering approximately 580,000 employees, 44% of whom had the UR program sometime during the period 1987 to 1990. Because of regression to the mean, UR savings were greater for units with higher prior use and smaller for units with lower use. In addition to prior use, the size of the group also determined the extent of regression to the mean. Groups with smaller number of enrollees had greater potential to save from the UR because of UR's ability to reduce the outliers.

Adolescent↗
PubMed2000

Measurements of concentration dependence and enantiomeric purity of terpene solutions as a test of a new commercial VCD spectrometer

Vibrational circular dichroism (VCD) spectra of (+)-alpha-pinene solutions in carbon tetrachloride have been measured in the range of volume fractions 5-100% (v/v) in the mid-infrared region. The concentration dependence measured was statistically analyzed with the aim of obtaining a reliable correlation between the VCD band areas and the concentrations of individual enantiomers. The quality of the spectra was estimated by means of noise spectra which were defined as half the difference of the two following blocks of scans. In addition to this, the enantiomeric purity was studied. This study was carried out for both (+)- and (-)-alpha-pinene enantiomers in the range of the percent enantiomeric excess in the interval 10-100%. The relationship between VCD intensity and enantiomeric purity was determined by least-square regression and statistically evaluated. All measurements performed in this study were intended as a basic tool for testing of a new commercial VCD setup from Bruker. Copyright 2000 Wiley-Liss, Inc.

Journal Article↗