Analysis Of Covariance Techniques Research Articles

Evaluation of the effects of Telone II (fumigation) on nitrogen management and yield in Louisiana delta cotton

The objective of this paper is to evaluate Cotton, Gossypium hirsutum L. yield as affected by early season pests infesting alluvial soil within the Commerce-Bruin-Dundee soil series in Louisiana, USA. Novel methodology helped determine the effect of nematicide and selected fertility management practices on cotton lint yield collected from research plots and an on-farm test. In the small plot research test, data collected for thrips, nematodes and yield is analyzed using geo-referenced data points. Yields were significantly better in fumigation and nematicide seed treatments as compared to the non-treated plus high fertility management strategy that contained 144 kg/ha N, but more variation in yield occurred in the fumigation treatment with lower fertility management. In an embedded field trial that included three fertility management strategies (96, 138, 162 kg/ha N) applied with and without fumigation, linear mixed models analysis of co-variance techniques resulted in prescriptions for site-specific management of fumigation and fertilizer whereas conventional analysis could not be used for site-specific management.

Mechanical stability of structured bone grafts from the anterior iliac crest

Background The anterior part of the iliac crest is frequently used as a donor site for autogenous bone grafts. Depending on the clinical scenario, the grafts are exposed to compression and shear stresses. Insufficient stability of a bone graft can lead to the collapse of a reconstruction. The object of this study was to quantify the influence of surgery-related parameters like the bony composition (cancellous, unicortical and bicortical), the donor site and the angle of removal on the failure load of the bone plugs (shearing and compression tests). Methods A total of 137 bone cylinders varying in bony composition and in their angles to the trajectories in the anterior iliac crest were taken from 48 human hemipelvises with diamond hollow cutters. The failure load was measured in a standardized manner, each bone plug being subjected to two shear tests and three compression tests. Possible differences between groups were evaluated using analysis of covariance techniques with BMI, bone density and cortical thickness as covariates. The statistical significance level was set to 5% ( P < 0.05), no adjustment for multiple comparisons was done due to the descriptive nature of the study. Findings Bicortical bone plugs were more resistant than unicortical plugs to both compression and shear stress, and both were more stable than cancellous bone plugs ( P < 0.05). On average, the compression failure load was about twice as high as the corresponding failure load with shearing tests: the factor was approximately 1.5 for cancellous, approximately 2 for unicortical and approximately 3 for bicortical bone plugs. We could not find a significant effect of the precise donor site and the angle of removal (parallel or perpendicular to the crista) on the mechanical stability of cancellous bone plugs. Interpretation Surgeons should rather focus on the cancellous or cortical composition of the graft than location of the harvesting site or drilling angle in order to obtain a useful bone plug from the iliac crest.

Linear Covariance Techniques for Orbital Rendezvous Analysis and Autonomous Onboard Mission Planning

A novel trajectory control and navigation analysis software approach is developed. The program quickly determines trajectory dispersions, navigation errors, and required maneuver Δv at selected key points along a nominal trajectory. It can be used for mission design and planning activities or in autonomous flight systems to help determine the best trajectories, the best maneuver locations, and the best navigation update times to ensure mission success. These features are illustrated with two simple examples. The software works by applying linear covariance analysis techniques to a closed-loop guidance, navigation, and control (GN&C) system. The nonlinear dynamics and flight software models of a closed-loop six-degree-of-freedom Monte Carlo simulation are linearized. Then, linear covariance techniques are used to produce a program that will accurately predict 3-σ trajectory dispersions, navigation errors, and Av variations. Although the application presented is orbital rendezvous, the tools, techniques, and mathematical formulations are applicable to a variety of other space missions and GN&C problems including atmospheric entry, low-thrust electric propulsion missions, translunar injection and lunar orbit insertion, lunar ascent/descent, and formation-flying missions.

Providing Health Care Services to the Formerly Homeless: A Quasi-Experimental Evaluation

We performed a quasi-experiment to assess the effects of a focused health care intervention delivered in transitional housing facilities in Sacramento, California. Four transitional housing facilities (THFs) receiving the intervention were compared with 2 THFs that did not receive it. A multidisciplinary team provided a diverse package of services to residents at the intervention sites. Residents at comparison sites received usual care. Survey and physical examination data were collected in repeated cross-sectional surveys at baseline (pre-intervention) and after 6 and 18 months of follow-up (post-intervention). Using analysis of covariance techniques, our statistical models showed improved odds of receiving recommended gynecologic preventive care and decreased odds of frequent Emergency Department use at 18 months among residents at the intervention sites. At 6 months, residents at the intervention sites also experienced improved blood pressure control. There was no intervention effect on residents' access to specialists or on physical functioning, mental health, or dental health.

Use of a Covariance Analysis Technique for Predicting Performance of Regional-Area Differential Code and Carrier-Phase Networks*

ABSTRACT: There is currently great interest in using regional-area reference receiver networks (on the order of hundreds of kilometers) to perform precise (10 cm or better) kinematic positioning using GPS carrier-phase measurements. When designing or using such a network, it is important to be able to determine design trade-offs by predicting what the errors will be under various network configurations (e.g., number/geometry of receivers, ionospheric levels). This paper presents a method for predicting the level of differential (double-difference) code and carrier-phase errors that is capable of taking all these considerations into account. This method uses a covariance analysis technique, which is based on a network differential algorithm that minimizes the differential error variances (the NetAdjust method). After validation, this method is applied to a number of what-if scenarios, demonstrating the usefulness of the approach when designing or using a regional-area differential GPS network for precise positioning.

Physical Functioning and Depression Among Older Persons with Cancer

Purpose: The purpose of this study was to help identify factors to assess which elderly patients are likely to experience problems with physical and psychological functioning in association with cancer or its treatment.description of Study: A study was undertaken with a sample of 420 patients with cancer who were between the ages of 65 and 98 years and had received an incident diagnosis of breast, colon, lung, or prostate cancer. An analysis of covariance technique was used to determine how cancer site, treatment type, stage of disease, gender, age, comorbidity, symptom severity, and prediagnosis levels of physical functioning were related to physical functioning deficit, and how all of these in turn influenced patient depressive symptomatology.Results: Prediagnosis physical functioning, symptom severity, and days since surgery were significant predictors of physical functioning deficit. Patients who had been treated only with surgery experienced greater physical functioning deficits than did patients who had received both surgery and adjuvant therapy. This apparent anomaly was partly explained by the time interval from surgery to interview. Higher levels of symptom severity, lower levels of prior physical functioning, and greater physical functioning deficits all predicted higher levels of depressive symptomatology.clinical Implications: In the care of elderly patients with cancer, it is important for healthcare providers to consider the prediagnosis levels of physical functioning of patients with cancer to understand and anticipate the physical and psychological consequences of cancer and its treatment. Equally important is the proper management of patient symptoms in maximizing both the physical and psychological quality of life.

Physical Functioning and Depression Among Older Persons with Cancer

The purpose of this study was to help identify factors to assess which elderly patients are likely to experience problems with physical and psychological functioning in association with cancer or its treatment. A study was undertaken with a sample of 420 patients with cancer who were between the ages of 65 and 98 years and had received an incident diagnosis of breast, colon, lung, or prostate cancer. An analysis of covariance technique was used to determine how cancer site, treatment type, stage of disease, gender, age, comorbidity, symptom severity, and pre-diagnosis levels of physical functioning were related to physical functioning deficit, and how all of these in turn influenced patient depressive symptomatology. Pre-diagnosis physical functioning, symptom severity, and days since surgery were significant predictors of physical functioning deficit. Patients who had been treated only with surgery experienced greater physical functioning deficits than did patients who had received both surgery and adjuvant therapy. This apparent anomaly was partly explained by the time interval from surgery to interview. Higher levels of symptom severity, lower levels of prior physical functioning, and greater physical functioning deficits all predicted higher levels of depressive symptomatology. In the care of elderly patients with cancer, it is important for healthcare providers to consider the pre-diagnosis levels of physical functioning of patients with cancer to understand and anticipate the physical and psychological consequences of cancer and its treatment. Equally important is the proper management of patient symptoms in maximizing both the physical and psychological quality of life.

Performance of Modified Test Statistics in Covariance and Correlation Structure Analysis Under Conditions of Multivariate Nonnormality

Questions of whether hypothesized structure models are appropriate representations of the pattern of association among a group of variables can be addressed using a wide variety of statistical procedures. These procedures include covariance structure analysis techniques and correlation structure analysis techniques, in which covariance structure procedures are based on distribution theory for covariances, and correlation structure procedures are based on distribution theory for correlations. The present article provides an overview of standard and modified normal theory and asymptotically distribution-free covariance and correlation structure analysis techniques and also details Monte Carlo simulation results on the Type I and Type II error control as a function of structure model type, number of variables in the model, sample size, and distributional nonnormality. The present Monte Carlo simulation demonstrates clearly that the robustness and nonrobustness of structure analysis techniques vary as a function of the structure of the model and the data conditions. Implications of these results for users of structure analysis techniques are considered in the context of current software availability.

Association of mammographically defined percent breast density with epidemiologic risk factors for breast cancer (United States).

Mammographically defined percent breast density is an important risk factor for breast cancer, but the epidemiology of this trait is poorly understood. Although several studies have investigated the associations between reproductive factors and density, few data are available on the associations of breast density and waist-to-hip ratio (WHR), physical activity, education, alcohol and smoking. We investigated the associations of known and suspected breast cancer risk factors with breast density in a large breast cancer family study. Information was collected on members of 426 families through telephone interviews, mailed questionnaires and mammography. Mammographic films on 1900 women were digitized and breast density was estimated in discrete five-unit increments by one radiologist. Analysis of covariance techniques were used and all analyses were performed stratified by menopausal status. Similar to other reports, nulliparity, late age at first birth, younger age and lower body mass index were associated with increased percent density in both premenopausal and postmenopausal women, and hormone replacement therapy among postmenopausal women. Higher levels of alcohol consumption and low WHR were associated with increased percent density among both premenopausal and postmenopausal women (differences of 3-11% between high and low categories). However, smoking and education were inversely associated with percent density among premenopausal (p = 0.004 and p = 0.003, respectively) but not postmenopausal women (p = 0.52 and p = 0.90). Physical activity was not associated with percent density in either stratum (p values > 0.25). Combined, these factors explained approximately 37% of the variability in the percent density measure in premenopausal women and 19% in postmenopausal women. Many of these factors may potentially affect breast cancer risk through their effect on percent breast density.

The Dynamics of Senatorial Representation, 1952-1991

We propose a dynamic model of representation that posits that representatives adapt through time to minimize the distance between policy choices and constituent, global, and personal preferences. Several hypotheses flow from the dynamic model: (1) equilibria develop through time in senator policy choice; (2) representatives adapt through time to global, as well as constituent preferences; (3) the manner in which adaptation occurs depends on the strength of the representative's personal ideology; (4) the manner in which adaptation occurs depends on various measures of constituency efficiency. We use pooled time-series cross-section analysis of covariance techniques to evaluate the preceding hypotheses. The analysis shows that senators integrate constituent, global, and personal preferences. Equilibria exist through time in Senator Policy Liberalism Adaptation to and from the equilibria depends on global and constituent preferences and efficiency. The manner of adaptation also depends on the strength of the...

Avoiding Type II error in assessing lead toxicity plaintiffs

This article discusses statistical parallels between excessive conservatism and insufficient conservatism in rendering forensic opinions. The elements of a tort are reviewed and their relation to psychological and psychiatric opinions is also discussed, as are psychometric and clinical approaches to assessment of impairment and causation in individual lead poisoned children. It is argued that assessments in lead poisoning cases consisting solely of cranial nerve examinations result in considerable Type II Error. Sources of Type II Error in research using analysis of covariance techniques to study the toxic effects of lead include variance stealing, use of excessive numbers of covariates, lack of attention to interactions, and use of covariates that are actually substitute measures of lead ingestion. When experts cite nonsignificant findings of studies of low-level lead exposure, it inappropriately negates lead effects in more severely lead poisoned plaintiffs. In true experimental studies where there is no ambiguity regarding causation, the destructive effects of lead are quite clear. © 1998 John Wiley & Sons, Ltd.

Changes in Blood Cholesterol Awareness: Final Results From the South Carolina Cardiovascular Disease Prevention Project

We examined changes in five indicators of blood cholesterol awareness in two comparable biracial communities in South Carolina. One community received three years of cholesterol education and intervention activities implemented by a state health department and the other served as a comparison. Cross-sectional, interviewer-administered, random digit-dialed telephone surveys of 11,070 adults 18 years and older were conducted in 1987, 1988, 1989, and 1991. Changes in community levels of knowledge, preventive behavior, risk awareness, and treatment were assessed and compared between the two communities with analysis of covariance techniques that adjusted for age, race, and sex. Significant increases in knowledge, behavior, and risk awareness were observed for most groups defined by race, sex, or age in both communities. Significant net intervention increases between 1987 and 1991 were seen for knowledge of good cholesterol level (+16.4%, P < .001); behavioral action of ever having blood cholesterol checked (+18.6%, P < .001); and knowledge of personal level of blood cholesterol (+16.0%, P < .01). These results suggest that a community-wide blood cholesterol screening and education program can be effective in increasing blood cholesterol knowledge, risk awareness, and preventive behavior, thus serving as part of a public health strategy to lower and treat high blood cholesterol levels in a community.

The adverse effect of marginally higher lead level on intelligence development of children: a Shanghai study.

We surveyed 128 preschool children in a lead-polluted area in Shanghai to study the relationship between blood lead level and neuropsychological functions, assessed by age-appropriate psychological tests. The geometric means of blood lead level was 21.7 + -10.8 micrograms/dl. Of 47 children aged below 30 months, there was no significant difference in BSID indices between the high and low lead subjects, although the high lead children tended to have poorer development scores than the low lead ones. On the other hand, of 81 children older than 46 months, the WPPSI IQ scores showed highly significant negative correlation with blood lead level. Step-wise regression and multiple analysis of covariance techniques were employed to find out and control the confounding factors. Even when 21 non-lead variables were considered, the IQ difference between high and low lead groups remained statistically significant. We concluded that the children, especially those older than 46 months, in the area investigated, did suffer from lead toxicity causing impairment in intelligence development. We support the view that marginally higher lead level in children should be taken seriously.

The auditory P300 correlates with specific cognitive deficits in Parkinson's disease

An abnormally prolonged latency of the P 300 event-related potential has been reported in several types of dementing illnesses, including Parkinson's disease (PD). While some PD patients have dementia, a significant number of PD patients have less severe cognitive impairments. We examined the relationship between the auditory P 300 and a neuropsychological battery of 11 tasks in 43 PD patients. The quantitative relationship between the individual neuropsychological measures and the P 300 was examined using partial correlation and analysis of covariance techniques which controlled for age, education, and illness duration. The strongest correlations were between P 300 and both short-term memory and visual perception. Global cognitive deficits do not appear to relate to the abnormal P 300 responses in PD: instead, specific aspects of cognitive decline accounted for the electrophysiological abnormalities. An abnormally long or absent P 300 correlated with deficits on select cognitive tasks: those involving memory, visual perception, and abstract reasoning. The interactions between anatomical and neurochemical abnormalities in PD are discussed in light of the pattern of deficits seen in this study.

Differences in moral values between corporations

This research compares the importance of moral values for corporations' managements, as reported by 97 knowledgeable employees in eight corporations. Does an employee consensus emerge within corporations and does it differ between corporations? To answer this question, an analysis of covariance technique was used to compare the importance of moral values between corporations versus within corporations. Results corroborate the hypothesis that closely matched corporations do differ significantly from one another in the importance of prevailing moral values. Evidence also suggests that the importance of prevailing moral values may be inversely related with company size. Implications for future research and for the practice of management are delineated.

Parallel line analysis: multifunctional software for the biomedical sciences

An easy to use, interactive FORTRAN program for analyzing the results of parallel line assays is described. The program is menu driven and consists of five major components: data entry, data editing, manual analysis, manual plotting, and automatic analysis and plotting. Data can be entered from the terminal or from previously created data files. The data editing portion of the program is used to inspect and modify data and to statistically identify outliers. The manual analysis component is used to test the assumptions necessary for parallel line assays using analysis of covariance techniques and to determine potency ratios with confidence limits. The manual plotting component provides a graphic display of the data on the terminal screen or on a standard line printer. The automatic portion runs through multiple analyses without operator input. Data may be saved in a special file to expedite input at a future time.

Design and optimization of truck suspensions using covariance analysis

The optimization of a six-degree-of-freedom plane linear heavy truck model subject to normally distributed stationary random road excitations is discussed. The analysis makes use of the technique of covariance analysis to obtain the variances of the state variables. A mathematical programming technique for the design of vehicle suspension systems is formulated and a computer program is developed for the optimization of vehicle suspension parameters to make vehicle response a minimum.

A comparison of nonparametric analysis of covariance techniques

A small sample Monte Carlo simulation provides the means of comparison for several nonparametric alternatives to the standard analysis of covariance. A completely ran-domized design with samples from K populations and one co-variate is used for this study. The simulation evaluates the robustness of the techniques as well as the power to detect differences among the populations. The study indi-cates that a modification of existing nonparametric proce-dures yields a test that performs well in many situations

A Procedure for Optimization of Truck Suspensions

SUMMARY The purpose of this paper is to develop a procedure based on covariance analysis and nonlinear programming techniques which can be used for the parameter selection of optimum truck suspensions. The procedure is applied to explore the differences in parameter selection caused by the changes in the frequency content of the road input or by changes in the criteria for optimization. The equations of motion for a tractor-semitrailer truck are cast in state space form. The road excitations are represented by the output of a white noise excited shaping filter taking into consideration the time delays between the different vehicle axles. Shape filters to represent human perception of vibration in both the vertical and longitudinal directions in the time domain are presented and realized in terms of state variables. The suspension parameters of the road-vehicle-human body system are optimized using a direct search algorithm.

An Application of Covariance Technique in Diallel Crosses for Griffing Method I &amp; III

AbstractIn the present investigation, the analysis of Covariance technique has been applied to method I &amp; III of GRIFFING (1956) of diallel crosses for obtaining the precised estimates of general combining ability (g.c.a), specific combining ability (s.c.a) and reciprocal differences. The adjusted estimates of g.c.a, s.c.a and reciprocal differences and sum of squares due to these parameters and variances due to the estimates of parameters and their comparisons are also derived. The gain in precision in estimating the parameters due to the use of covariance technique has been illustrated with the help of an example.