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PubMed2002

Regression analysis of multiple-source longitudinal outcomes: a "Stirling County" depression study.

Epidemiologic studies of psychiatric disorders have increasingly relied on multiple sources of information to improve the validity of diagnoses and repeated assessments over time to provide a longitudinal perspective. In this paper, the authors present a general multivariate logistic regression method for the simultaneous analysis of discrete outcomes that exhibit such features. This approach permits risk factor and agreement analyses within a unified framework and appropriately uses data from subjects who may be missing some outcomes. The authors use this approach to analyze data from a "Stirling County" study of depression. During a 3- to 4-year period in the early 1990s, 631 subjects were assessed in two separate interviews, on each occasion with two diagnostic schedules (the DePression and AnXiety schedule (DPAX) and the Diagnostic Interview Schedule (DIS)). The female:male ratio of depression was found to be different for the DPAX and the DIS (0.8 and 1.6, respectively). Education was inversely associated with depression, while the effects of time, the subject's age, and the interviewer's sex were essentially null. With respect to the outcomes' association, agreement between the DPAX and the DIS was low. In addition, stability of the DPAX over time was significantly higher than that of the DIS. No covariates were found to affect significantly the association between outcomes.

Adult↗
PubMed1999

[Quality of life as a time-dependent covariable in cox regression analysis and its application].

OBJECTIVE: To present a statistical method for combined evaluation of the quality of life and survival time and to study some issues in its application. METHODS: Based on Cox regression model, quality of life was used as a time-dependent covariable in analysis of the influence factors for the effectiveness of detoxification in 212 drug addicts. RESULTS: The influence factors entered the regression equation were ways of detoxification for drug abusers, marital status, mode of drug abuse, frequency of detoxification, maternal educational level, maternal occupation, family atmosphere and help and encourage from their relatives and friends, with their hazard ratios of 0.673, 1.315, 1.319, 0.867, 1.120, 1.318, 0.724 and 1.150, respectively. CONCLUSION: Combined statistical analysis of quality of life and survival time was a better method for the evaluation of the effectiveness of detoxification and its influence factors, which depended mainly on their mother's qualification, family atmosphere, mode and length of drug abuse, etc.

Humans↗
PubMed2006

Prediction of the ripening times of ewe's milk cheese by multivariate regression analysis of capillary electrophoresis casein fractions.

The effect of the ripening time on the proteolytic process in cheeses made from ewe's milk during a 139-day ripening period was monitored by the use of capillary electrophoresis of pH 4.6 insoluble fraction. Totals of 18 and 21 peaks were recognized and matched in the electropherograms obtained with a fused-silica capillary and a neutral capillary (hydrophilically coated), respectively. These peaks correspond to intact ovine caseins and their hydrolysis products (alpha(s1)-casein I, alpha(s1)-casein II, alpha(s1)-casein III, alpha(s2)-casein, beta(1)-casein, beta(2)-casein, p-kappa-casein, alpha(s1)-I-casein, gamma(1)-casein, gamma(2)-casein, and gamma(3)-casein). The alpha(s)-caseins (alpha(s1)- and alpha(s2)-casein) displayed similar degradation pattern to one another, but different from those of beta-caseins (beta(1)- and beta(2)-casein). beta-Caseins were very much undergoing lesser degradation during the ripening time than alpha(s)-casein. Finally, partial least-squares regression and principal components regression were used to predict the ripening time in cheeses. The models obtained yielded good results since the root-mean-square error in prediction by cross validation was <8.6 days in all cases.

Analysis of Variance↗
PubMed1997

A regression analysis of filler particle content to predict composite wear.

STATEMENT OF PROBLEM: It has been hypothesized that composite wear is correlated to filler particle content. There is a paucity of research to substantiate this theory despite numerous projects evaluating the correlation. PURPOSE OF STUDY: The purpose of this study was to determine whether a linear relationship existed between composite wear and filler particle content of 12 composites. MATERIAL AND METHODS: In vivo wear data had been previously collected for the 12 composites and served as basis for this study. Scanning electron microscopy and backscatter electron imaging were combined with digital imaging analysis to develop "profile maps" of the filler particle composition of the composites. These profile maps included eight parameters: (1) total number of filler particles/28742.6 microns2, (2) percent of area occupied by all of the filler particles, (3) mean filler particle size, (4) percent of area occupied by the matrix, (5) percent of area occupied by filler particles, r (radius) 1.0 < or = micron, (6) percent of area occupied by filler particles, r = 1.0 < or = 4.5 microns, (7) percent of area occupied by filler particles, r = 4.5 < or = 10 microns, and (8) percent of area occupied by filler particles, r > 10 microns. Forward stepwise regression analyses were used with composite wear as the dependent variable and the eight parameters as independent variables. RESULTS: The results revealed a linear relationship between composite wear and the filler particle content. CONCLUSION: A mathematical formula was developed to predict composite wear.

Analysis of Variance↗
PubMed2006

A meta-regression analysis of treatment effect modifiers in trials with flexible-dose oral sildenafil for erectile dysfunction in broad-spectrum populations.

Several trials and reviews provide evidence for the efficacy of phosphodiesterase-5 inhibitors in the treatment of erectile dysfunction (ED). However, little is known about the impact of treatment effect modifiers other than concomitant diseases. Our objective was to identify patient and trial characteristics as well as methodological and publication-related issues that are associated with the treatment effect measured in flexible-dose randomized controlled trials of oral sildenafil for ED. The MEDLINE and the Cochrane Central databases were searched for efficacy trials of sildenafil. Thirteen trials fulfilled all inclusion criteria. A series of meta-regression and graphical analyses were performed to test the impact of possible effect modifiers. Treatment effect was influenced by mean baseline disease severity and mean duration of the disease. These associations were at least partly mediated by placebo response. Trial duration, age of patients and etiology of ED in patients did not have any significant influence on the treatment effect. The year of publication of primary trials was also related to trial findings. Our analysis adds important data to enable the control of confounding variables in future trials and meta-analyses. It might also help the individual to assess the unbiased efficacy and true innovative potential of available and forthcoming pharmacological agents.

Administration, Oral↗
PubMed1997

Retirement patterns in Hong Kong: a censored regression analysis.

"This paper provides an overview of retirement patterns in Hong Kong on the basis of limited data. A censored regression model is used to infer the retirement age from people's current retirement status and their current age. This model is equivalent to a restricted probit model, and the interpretation of parameters is straightforward. The results clearly show a negative income effect on the retirement decision. The retirement age seems to be positively related to lifetime earnings but negatively related to the rate of decline of earnings with age."

Age Factors↗
PubMed1986

Quantitative electron microscope autoradiography: application of multiple linear regression analysis.

A new method for the analysis of high resolution EM autoradiographs is described. It identifies labelled cell organelle profiles in sections on a strictly statistical basis and provides accurate estimates for their radioactivity without the need to make any assumptions about their size, shape and spatial arrangement. The radioactivity in interfacial membranes and transitional junctional regions between pairs of adjoining cell structures can be determined without any additional measurements. The uniformity of internal labelling of large cell organelles can be also assessed. Correcting for cross-fire does not need any predictive information from a frequency distribution function describing the image spread about a radioactive point source. Instead, the section area is subdivided into regions in such a way that each region with cross-fired silver grains over it includes also the sites of the radioactive disintegrations that have produced them. The method is based on the quantitative regression relationship between the number of developed silver grains overlying any given region and the size of the cell organelle profiles included. A transparent overlay screen bearing a regular array of circles and a point-counting procedure are applied to divide the section area into regions and to measure their area and the size of the cell organelle profiles. The least squares method is used for the simple and rapid calculation of specific activity estimates and exact standard errors to be attached to them. A modest computing facility and a standard library program are required. Simulation modelling and analysis of residuals were used to lend support to the validity of the method.

Animals↗
PubMed2000

Regression analysis of time trends in perinatal mortality in Germany 1980-1993.

Numerous investigations have been carried out on the possible impact of the Chernobyl accident on the prevalence of anomalies at birth and on perinatal mortality. In many cases the studies were aimed at the detection of differences of pregnancy outcome measurements between regions or time periods. Most authors conclude that there is no evidence of a detrimental physical effect on congenital anomalies or other outcomes of pregnancy following the accident. In this paper, we report on statistical analyses of time trends of perinatal mortality in Germany. Our main intention is to investigate whether perinatal mortality, as reflected in official records, was increased in 1987 as a possible effect of the Chernobyl accident. We show that, in Germany as a whole, there was a significantly elevated perinatal mortality proportion in 1987 as compared to the trend function. The increase is 4.8% (p = 0.0046) of the expected perinatal death proportion for 1987. Even more pronounced levels of 8.2% (p = 0. 0458) and 8.5% (p = 0.0702) may be found in the higher contaminated areas of the former German Democratic Republic (GDR), including West Berlin, and of Bavaria, respectively. To investigate the impact of statistical models on results, we applied three standard regression techniques. The observed significant increase in 1987 is independent of the statistical model used. Stillbirth proportions show essentially the same behavior as perinatal death proportions, but the results for all of Germany are nonsignificant due to the smaller numbers involved. Analysis of the association of stillbirth proportions with the (137)Cs deposition on a district level in Bavaria discloses a significant relationship. Our results are in contrast to those of many analyses of the health consequences of the Chernobyl accident and contradict the present radiobiologic knowledge. As we are dealing with highly aggregated data, other causes or artifacts may explain the observed effects. Hence, the findings should be interpreted with caution, and further independent evidence should be sought.

Female↗
PubMed1980

Stepwise regression analysis of an intensive 1-year study of delirium tremens.

An intensive 1-year study was carried out on 41 male patients, mean age 49, mean hospitalization time 49 days, admitted to a special ward of the Beckomberga Hospital with the diagnosis of delirium tremens and 50 concomitant somatic and psychiatric diagnoses (1--9 per capita), and given a standardized treatment. The mean duration of delirium tremens after admission was 2 days; 76% recovered within 48 h. The duration after admission was positively correlated to age, number of previous delirium tremens, negatively correlated to B-haemoglobin and B-haematocrit for laboratory data obtained within the first 24 h and was positively correlated to blood sugar and S-creatinine on data taken within 40 h (Pearson correlation matrix). Stepwise multiple regression (SWR) based on 46 quantitative and dummy variables (the latter used to represent the presence of various concomitant diseases) was employed to identify the factors predicting the duration of delirium tremens. On final SWR analysis, which limited the number of observations to cases with complete observation vectors, the following regression equation was obtained: Duration after admission = 3.57--0.93 (S-magnesium)--0.29 (B-eosinophils) + 0.62 (liver disease), P greater than 0.05, n = 14. Although the regression coefficients were not statistically significant, S-magnesium, negatively associated with the duration after admission, offered 20% out of the total 38% of explanation given, whereas B-eosinophils, negatively associated, offered 12%, and liver disease, positively associated, 6%. The choice by the SWR program of S-magnesium as the most important factor in predicting the duration of delirium tremens is consistent with clinical evidence that alcohol ingestion causes magnesium diuresis and that magnesium deficiency is present in chronic alcoholism. In view of this knowledge, it is reasonable to assume that the lack of statistical significance is due to the small sample size rather than to the alternative that no explanation is offered by S-magnesium. Furthermore, B-haemoglobin, S-potassium, S-ASAT, and S-ALAT, known to be characteristically altered in delirium tremens, were found on forcing (a variant of SWR) to be of secondary importance to S-magnesium as explaining factors, whereas blood sugar and S-creatinine derived part of their explaining power from S-magnesium. In conclusion, extensive use of SWR analysis based on 46 potential explaining variables points to serum magnesium concentration as the most important factor in predicting the duration of delirium tremens.

Adult↗
PubMed1997

Reducing a spatial database to its effective dimensionality for logistic-regression analysis of incidence of livestock disease.

Large databases with multiple variables, selected because they are available and might provide an insight into establishing causal relationships, are often difficult to analyse and interpret because of multicollinearity. The objective of this study was to reduce the dimensionality of a multivariable spatial database of Zimbabwe, containing many environmental variables that were collected to predict the distribution of outbreaks of theileriosis (the tick-borne infection of cattle caused by Theileria parva and transmitted by the brown ear tick). Principal-component analysis and varimax rotation of the principal components were first used to select a reduced number of variables. The logistic-regression model was evaluated by appropriate goodness-of-fit tests.

Animals↗
PubMed1993

Regression analysis of current-status data: an application to breast-feeding.

"Although techniques for calculating mean survival time from current-status data are well known, their use in multiple regression models is somewhat troublesome. Using data on current breast-feeding behavior, this article considers a number of techniques that have been suggested in the literature, including parametric, nonparametric, and semiparametric models as well as the application of standard schedules. Models are tested in both proportional-odds and proportional-hazards frameworks....I fit [the] models to current status data on breast-feeding from the Demographic and Health Survey (DHS) in six countries: two African (Mali and Ondo State, Nigeria), two Asian (Indonesia and Sri Lanka), and two Latin American (Colombia and Peru)."

Africa↗
PubMed2003

Linear regression analysis and its application to the multivariate spectral calibrations for the multiresolution of a ternary mixture of caffeine, paracetamol and metamizol in tablets.

The multivariate spectral calibration methods, tri-linear regression-calibration (TLRC) and multi-linear regression-calibration (MLRC) were developed for the multiresolution of a ternary mixture of caffeine (CAF), paracetamol (APAP), metamizol (MET), which have closely overlapped in the spectra. The calibration algorithms were briefly described for the three-component system, CAF-APAP-MET. By using the various synthetic mixtures of three compounds, the validity of the TLRC and MLRC methods was confirmed and applied to the real samples containing the above-mentioned compounds in two different commercial tablet formulations. The TLCR and MLRC methods which are very rapid, easy to apply, yet not expensive, are powerful tools with very simple mathematical contents for multiresolution of the three- or multi-component mixture systems. The data treatments were carried out by the MAPLE V, EXCEL and SPSS 10.0 Softwares. The obtained results were successfully compared with each other as well as with those obtained by other literature methods.

Acetaminophen↗
PubMed2001

Multivariable regression analysis and other findings from the 1999 joint ASLAP/ACLAM economic survey of laboratory animal veterinarians.

Results from a 1999 economic survey of laboratory animal veterinarians were used to develop a multivariable linear regression model capable of predicting income in light of a large set of characteristics of veterinarians and their employers. When considered simultaneously, the variables of experience, supervisory responsibility, ACLAM board certification, geographic region, type of employer, size of animal facility, and job title provided the best model fit, in agreement with an earlier statistical model of income for persons in this profession. Aspects of the demographics of faculty appointments and secondary sources of professional income available to some laboratory animal veterinarians also were evaluated.

Animals↗
PubMed1994

Evaluating relative efficiencies of Veterans Affairs Medical Centers using data envelopment, ratio, and multiple regression analysis.

Several forms of analysis are used to evaluate the efficiency of acute care Veterans Affairs hospitals. The smaller hospitals with fewer than 100 beds and hospitals not in operation a full year have been excluded. The types of analysis used are input ratio analysis and productivity analysis of three outputs consisting of surgeries, discharges and emergency and outpatient visits. Also used is data envelopment analysis (DEA) of two subsamples segmented by whether the hospital is a member or not of the Council of Teaching Hospitals. Finally, multiple regression is used to find indicators of the relative efficiencies generated by the DEA. Results show that about one half of all hospitals are relatively inefficient. Also promising indicators of efficiency are hospital size, inpatient surgeries, outpatient surgeries, and the aggregate emergency room and outpatient visits.

Ambulatory Care↗
PubMed1988

Linear regression analysis of ultrasound follicular growth series: evidence for an abnormality of follicular growth in endometriosis patients.

Follicular diameter growth is a highly linear function of time. Recently, the potential utility of linear regression-derived parameters for describing and comparing cycles of follicular growth was described. The linearity of growth, growth rate constant (K), calculated date of growth onset (Do), total growth period (TGP), menstrual age at apparent ovulation (MAov), and peak follicular diameter (PFD) have been calculated from the follicular growth series of a group of patients with laparoscopically diagnosed endometriosis (n = 46). These parameters were compared with those of a group of normal volunteers (n = 18). The authors found significant differences between endometriosis patients and controls in follicular growth rate and total growth period. The effect of patients' clomiphene citrate usage on growth parameters in these patients was examined. Abnormalities in interrelationships between the growth parameters were detected, suggesting the possibility of subtle defects in the regulation of follicular growth in these patients.

Endometriosis↗
PubMed2005

[Partial least-squares regression analysis for simultaneous spectrophotometric determination of Fe3+ and Al3+].

Adding hexodecyltrimethylammonium bromide(CTMAB) to improve solubility and delicacy, and using chromazurol S as a chromogenic reagent, and acetone as a stabilizing reagent, partial least-squares regression(PLS) was used to determine simultaneously trace amounts of Fe(III) and Al(III) in sythetic samples. Considering the stability of the rays, and the absorption properties of the two ingredients, seven wavelengths between 610 and 670 nm were selected for data collection. As a comparison, the methods of CPA and PLS were used respectively for analysing the data obtained from the experiment, and the results suggested that the latter was much better.

Algorithms↗