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PubMed2006

A comparative study of linear and non-linear regression analysis for ammonium exchange by clinoptilolite zeolite.

Ammonium ion exchange from aqueous solution using clinoptilolite zeolite was investigated at laboratory scale. Batch experimental studies were conducted to evaluate the effect of various parameters such as pH, zeolite dosage, contact time, initial ammonium concentration and temperature. Freundlich and Langmuir isotherm models and pseudo-second-order model were fitted to experimental data. Linear and non-linear regression methods were compared to determine the best fitting of isotherm and kinetic model to experimental data. The rate limiting mechanism of ammonium uptake by zeolite was determined as chemical exchange. Non-linear regression has better performance for analyzing experimental data and Freundlich model was better than Langmuir to represent equilibrium data.

Hydrogen-Ion Concentration↗
PubMed1976

Effects in the rat of environmental temperature, diet dilution and treadmill running on voluntary food intake, body composition and endocrine organ mass: a multiple regression analysis.

The effects upon weight gain, food intake, carcass composition, and weight of pituitary, adrenals, and testes of male rats subjected to three environmental temperatures (T; 16.0 degrees, 23.5 degrees, and 31.0 degrees), five diet dilution rates (D; 0%, 12.5% 25.0%, 37.5%, and 50.0%), and five daily treadmill running periods (E; 10 minutes, 40 minutes, 70 minutes, 100 minutes, and 130 minutes) were studied by multiple regression techniques. Equations describing regression surfaces could contain significant linear and/or quadratic coefficients of the independent variables (T, D, and E) and their first order interactions. Body weight attained was reduced by increased D and T. Total food intake increased linearly with increases in D, but this increase was smaller for the rats in the higher environmental temperature since there was a significant DT interaction. Total food intake was decreased by increases in T. The intake of food minus diluent was maintained until D attained a value of 37.5%; beyond this point the rats at all three temperatures failed to maintain digestible energy intake. The data strongly suggested that the energy intake was not limited by the gastrointestinal tract capacity. E did not significantly affect food intake. Significant regression coefficients were found for the dependent variables of body dry matter, nitrogen, ash, ether extract, and energy and of the weight of depot fat pads, adrenals, and testes, as follows: (1) For D, there was no linear coefficient for body nitrogen. All remaining linear coefficients were negative except for body ash. The only quadratic coefficients (both positive) were for adrenal and testes weights (2) For E, all linear coeffcients were negative except those for body nitrogen, body ash, and adrenal weight. There were not quadratic coefficients for body nitrogen, body ash, adrenal weight, and testes weight. The remaining quadratic coefficients were all positive; (3) For T, there was no quadratic coefficient for body energy. The remaining linear coefficients were positive except those for fat deposit size, body ether extract, and adrenal weight. The remaining quadratic coefficients were negative except those for fat deposit size, body ether extract, and adrenal weight; (4) For the DE interaction, no coefficients were significant; (5) For the DT interaction, there were no significant coefficients for body nitrogen, fat depot size, or adrenal weight. The remaining coefficients were positive except for body ash; (6) For the ET interaction, the only significant coefficients were negative ones for body ether extract and body energy and a positive one for testes weight.

Adipose Tissue↗
PubMed1984

Regression analysis of nonlinear Arrhenius plots: an empirical model and a computer program.

The rates of most physical, chemical and biological processes vary with temperature and numerous instances have been reported in which Arrhenius plots of the experimental data appear to consist of two straight line segments joined by a relatively sharp break. An empirical model, based on a general hyperbola, is shown to be applicable to such systems; a nonlinear regression program is described which facilitates fitting of this function to experimental data which show either broad or sharp transitions. The program yields best estimates and standard errors of the temperature and ordinate value at the transition, and the two activation energies.

Computers↗
PubMed2004

Semi-parametric ROC regression analysis with placement values.

Advances in technology provide new diagnostic tests for early detection of disease. Frequently, these tests have continuous outcomes. One popular method to summarize the accuracy of such a test is the Receiver Operating Characteristic (ROC) curve. Methods for estimating ROC curves have long been available. To examine covariate effects, Pepe (1997, 2000) and Alonzo and Pepe (2002) proposed distribution-free approaches based on a parametric regression model for the ROC curve. Cai and Pepe (2002) extended the parametric ROC regression model by allowing an arbitrary non-parametric baseline function. In this paper, while we follow the same semi-parametric setting as in that paper, we highlight a new estimator that offers several improvements over the earlier work: superior efficiency, the ability to estimate the covariate effects without estimating the non-parametric baseline function and easy implementation with standard software. The methodology is applied to a case control dataset where we evaluate the accuracy of the prostate-specific antigen as a biomarker for early detection of prostate cancer. Simulation studies suggest that the new estimator under the semi-parametric model, while always being more robust, has efficiency that is comparable to or better than the Alonzo and Pepe (2002) estimator from the parametric model.

Case-Control Studies↗
PubMed1985

Regression analysis of changes in blood pressure with oral contraceptive use.

Measurements of blood pressure were obtained on 2,673 women from East Boston, Massachusetts, an urban, working class neighborhood, in surveys conducted in both 1973 and 1976-1977. Of these, 927 women participated in a third survey in 1978. The women were 16 to 49 years of age in 1973, premenopausal throughout the study, and not on blood pressure medication. Regression analyses were performed of blood pressure change between the first and second as well as between the second and third surveys on initial blood pressure, age, weight, and patterns of oral contraceptive use. For systolic pressure the effect of starting oral contraceptive use was an increase of 4.1 mmHg (p less than 0.0001), while the effect of discontinuing use relative to continued use was a 4.4 mmHg decrease (p less than 0.0001). These changes were not affected by duration of use or time since last use among past users. For diastolic pressure the average effect of starting use between surveys was an insignificant 1.0 mmHg increase, but diastolic pressure level seemed to increase with duration of use (0.5 mmHg/year, p = 0.0009). The effect of discontinuing use relative to continued use was a drop of 2.7 mmHg in diastolic pressure (p = 0.0004), which was uninfluenced by time since last use.

Adolescent↗
PubMed2005

Evidence that the relations between novelty-induced activity, locomotor stimulation and place preference induced by cocaine qualitatively depend upon the dose: a multiple regression analysis in inbred C57BL/6J mice.

It has been speculated that an individual's response to novelty is a reliable predictor of its vulnerability to develop addiction. However, the relationships between response to novelty and the development of drug-induced conditioned place preference are still unclear. The present study investigates the relationships between locomotor responses to novelty, cocaine-induced locomotor stimulation and conditioned place preference in C57BL/6J mice with multiple regression analyses. Four groups of mice receiving saline, 4, 8 or 12 mg/kg cocaine (i.p.) were submitted to an 8-day unbiased counterbalanced place conditioning protocol. Levels of locomotion on the pre-conditioning session were used as a score of locomotor response to a novel environment. The locomotor activity on the first cocaine-pairing session of the conditioning procedure served as a measure of the locomotion-activating response to a single injection of cocaine. Cocaine-induced dose-dependent locomotor stimulant effects and a significant place preference at all tested doses. A positive correlation was found between the locomotor responses to novelty and the locomotor stimulant effects of cocaine, but was significant only for the highest dose of cocaine (12 mg/kg). In contrast, there was a negative correlation between the locomotor response to novelty and the conditioned place preference induced by 4 mg/kg cocaine. Finally, the locomotor stimulant effects of cocaine do not correlate with cocaine-induced conditioned place preference at any tested dose of cocaine. The relationships between locomotor response to novelty and both cocaine-induced stimulant and rewarding effects can be differentially affected by the dose in inbred C57BL/6J mice.

Animals↗
PubMed2006

[Hierarchical regression analysis for relationship between job stress and job burnout in Shanghai employees].

OBJECTIVE: To identify related factors of job burnout in Shanghai employees. METHODS: Four hundred fifty-six employees in Shanghai were investigated in this study. Self-administered questionnaires were used to assess job burnout and job stress, based on Maslach Burnout Inventory and the Job Demand-Control model as well as Effort-Reward Imbalance Model. Hierarchical linear regression was employed to analyze the relationship of job burnout to personal characteristics and job stress. RESULTS: The indexes of three dimensions of job burnout were emotional exhaustion 19.70 +/- 8.92, depersonalization 11.95 +/- 4.45 and reduced personal accomplishment 28.10 +/- 10.08. Job stress was found to be affected differently in three dimensions of job burnout. Job demand, effort and over-commitment had positive impact on emotional exhaustion. Job control had a negative association with emotional exhaustion. There were significant relationship between depersonalization and age, sex and education of employees. Job control, reward and over-commitment affected the index of depersonalization. Education level and social support increased personal accomplishment index. CONCLUSION: It is necessary to reduce job stress and care about personal characteristics in preventing job burnout.

Adult↗
PubMed2001

Identifying significant predictors of student evaluations of faculty through hierarchical regression analysis.

College teachers' ages and personalities, and students' course grades, gender, enrollment status, academic abilities, and ages were investigated as predictors of student evaluations of faculty. An evaluation form containing 7 items reflecting the personality trait of extraversion and 8 items reflecting teaching effectiveness was used to collect data from 351 undergraduates. Teachers' extraversion (.79) and teachers' ages (-.08) were correlated highest, and students' gender was correlated lowest (.08) with teaching effectiveness. Hierarchical regression revealed that teachers' extraversion was the only significant predictor of student evaluations (beta = .76, p < .001) after controlling for enrollment status, course grades, and student ages.

Adolescent↗
PubMed2004

Predictive models of safety belt use: a regression analysis of MVOSS data.

A substantial portion of the U.S. population fails to regularly use their safety belts. The explanations for the differential belt use have addressed, for example, socioeconomics, state law, attitudes, and perceived likelihood of being ticketed. The current analyses create predictive models of safety belt use. Using NHTSA's Motor Vehicle Occupant Safety Surveys (Years 1998 and 2000; N = 9577), variables related to belt use were entered into backward stepwise logistic regressions to produce two predictive models (Demographic and Attitudinal) of safety belt use (Always versus Not always). The results indicated that belt use is a complicated issue as there were several interactions between variables. The Demographic predictive model contained main effects for, law types, socioeconomics, population density, a gender-law type interaction, and a three-way interaction between age, marital status, and vehicle type. The Attitudinal model included perceived effectiveness of the belt, fatalistic attitudes, and an interaction between perceived effectiveness of the belt and perceived risk of being ticketed. These models survived a multinomial logistic regression when belt use was parsed into three categories (Always, Part-time, and Infrequent). In addition to variables that affect belt use, the results suggested that the structure of "belt use" as a psychological/behavioral construct is more complicated than once thought. Specifically, a dichotomous breakdown of belt use (Always and Not always) oversimplifies the construct because the predictor factors sometimes affect "part-time" belt users differently than "infrequent" belt users (compared to "full-time" users). Many of the factors included in the models have been previously shown to impact belt use, but the interaction effects--indicating a more complicated relationship between these variables than previously suggested--may contribute to a better understanding of safety belt use.

Adolescent↗
PubMed2004

Regression analysis of trends in mortality from hepatocellular carcinoma in Japan, 1972-2001.

BACKGROUND: In Japan, higher mortality rates from hepatocellular carcinoma (HCC) have been observed than in any other industrialized country and the reported numbers of deaths due to HCC have increased significantly in recent years. We assessed whether there was a real increase in mortality from HCC and which factors contributed to the recent increasing trends of the number of deaths from HCC. METHODS: Poisson regression models were used to analyse panel data for the period 1972-2001. RESULTS: In both sexes, age-standardized mortality rates from HCC increased significantly over the past three decades. Among males the annual percentage increase in age-adjusted mortality rates was approximately 1-3% during the period 1972-96. On the other hand, female mortality trends were less clear. The estimated birth cohort effects suggested that there was a peak in the mortality risk among the cohorts born during the period 1927-36, which corresponded to those aged between 50-64 years during the period 1987-96. This was the period when a large increase of both age-specific mortality rates among older age groups and age-standardized mortality rates were observed particularly among males. CONCLUSIONS: This study shows that an upward trend of mortality from HCC in Japan was primarily due to the effects among birth cohorts born around 1930, which are consistent with the pattern of past exposure to hepatitis C virus. The cohort effects have contributed to a large increase in mortality from HCC in recent years and the number of deaths from HCC is expected to increase by 2010-15.

Adult↗
PubMed1985

Regression analysis of electromyographic activity of masticatory muscles versus bite force.

Electromyographic (EMG) activity of the superficial masseter and the anterior temporal muscles versus the bite force was studied in 10 young women. They were fully dentate and had no dysfunction of the stomatognathic system. The descending part of the trapezius muscle was also chosen for EMG registration. The average bite force between the first molars was 396 N (Newton). Steeper slopes for the EMG versus force regression curve at high contraction levels than at low contraction levels for the superficial masseter muscle may indicate that this muscle has a recruitment pattern that differs from that of the anterior temporal muscle. In the case of the anterior temporal muscle there was no difference between the slopes for the EMG-force regression at low and high contraction levels. There was significantly increased activity in the descending part of the trapezius muscle mainly during high bite force levels in half the subjects.

Adult↗
PubMed2001

[Regression analysis of idiopathic endothelial cell loss after perforating normal risk keratoplasty: basic principles for long-term analysis of endothelial risk factors in a retrospective clinical study].

BACKGROUND: For the characterisation of influencing factors on chronic endothelial cell loss after penetrating keratoplasty by means of multivariate statistics, a mathematical description of the course of the individual postoperative endothelial cell density is a prerequisite. This mathematical description should result in a standardized index value describing course and amount of the postoperative endothelial cell loss over time in a canonical way. The slopes of the linear regression lines for each individual scatter plot of a) the endothelial cell density values plotted against the respective postoperative time directly (linear regression), and b) after logarithmic transformation (exponential regression) are evaluated, respectively. PATIENTS AND METHODS: 58 patients after normal-risk keratoplasty (26x keratokonus, 22x Fuchs-dystrophy and 10 cases of corneal decompensation after cataract surgery) with 5 or more postoperatively acquired endothelial density values and without any episodes of graft rejection were included in this study. Mean follow up was 2.9 +/- 1.1 years. The postoperative endothelial cell density values were plotted against the respective time for each patient individually. The coefficients of variation (R2) derived from the linear and the exponential regression models were calculated for each of these scatter plots. The pairs of R2 values (linear vs. exponential) were compared statistically. A dependence of the difference of linear and exponential R2-values on the ophthalmologic diagnosis was tested as well. RESULTS: The linear model is able to declare 83% the total variance of the course of the endothelial cell density. The exponential model even declares 86%. This small difference was statistically significant. Since both methods of regression describe the course of the cell density well, intra/and extrapolation of missing endothelial values is possible with both models. No dependence of the difference of linear and exponential R2-values on the ophthalmologic diagnosis could be demonstrated. CONCLUSIONS: Both, the intuitively understandable slope of the linear regression line and the constant of decay of the exponential regression curve, are suitable for describing the amount of the postoperative loss of endothelial cells after normal-risk keratoplasty independent of the ophthalmologic diagnosis. Both can thus be used as target variable in forthcoming statistical analyses for chronic endothelial cell loss.

Adult↗