SEARCH · Search PubMed
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Computer analysis of hygienic standards in Russia and the USA and of the toxicometric parameters of chemicals characterized by predominantly irritating effects helped create a prognostic model for the calculation of maximum allowable concentrations of chemicals in the air of working zones.
This paper presents an analysis of the relationship between community characteristics, household attributes, and child survival in Brazil. The principal objectives are to investigate how the social and environmental context in which a child is raised affects his or her survival chances, and to analyze how household variables modify the effects of community characteristics. The interaction effects we examine help to explain the effects of community characteristics on child survival chances by illuminating the most likely pathways through which these covariates operate. This information is also useful for predicting who is most likely to benefit from public policies to improve community infrastructure, education, and health care.
OBJECTIVE: To evaluate the results of large clinical trials vs the pooled results of smaller trials. DATA IDENTIFICATION: Meta-analyses with at least 1 "large" study were identified from the Cochrane Pregnancy and Childbirth Database and from MEDLINE (1966-1995). STUDY SELECTION: We used a sample size approach to select 79 meta-analyses with at least 1 large study of 1000 or more patients. We used a statistical power approach to select 61 meta-analyses with at least 1 large study based on statistical power considerations. DATA EXTRACTION: The outcome of interest for each meta-analysis was the primary one stated in the original publication or, when not clearly specified, was decided on clinically. DATA SYNTHESIS: By random effects calculations, we found agreement between large and smaller trials in 90% of the meta-analyses selected by the sample size approach and in 82% of the meta-analyses selected by the statistical power approach. Twice as many disagreements appeared when the variability among large studies and among smaller studies was not considered (ie, fixed effects calculations). Of the 15 disagreements between results of large and smaller trials using the random effects model, plausible explanations were identified in 10 meta-analyses: 5 with differences in the control rate of events between large and smaller trials, 4 with specific protocol or study differences, and 1 with potential publication bias. Two other disagreements were not clinically important, and tentative reasons could be identified for 2 of the remaining 3 disagreements. CONCLUSIONS: Results of smaller studies are usually compatible with the results of large studies, but discrepancies do occur even when the diversity among both large studies and smaller studies is considered. Clinically important differences without a potential explanation are extremely uncommon. Future research should further examine sources of heterogeneity between the results of large and smaller trials.
Two single-pass methods for fitting multiexponentials to experimental data are described. These methods rely on the construction of a matrix whose characteristic polynomial is used to determine the rates of decay. In the first method, which we call the multiple-delay method, the matrix is constructed using time delays of the experimental data. This method is fast and highly accurate even if the experimental signal contains exponential components with similar rates of decay. In the second method, which we call the successive-integral method, the matrix is constructed using integrals of the experimental data. This procedure yields good results for noisy signals and is a generalization of the method of Martin et al. ((1993) J. Neurosci. Methods, 51: 135-146). In addition, a particular instability of the multiexponential curve fitting problem is identified and a method for overcoming this instability is given.
Long-term complications of Insulin Dependent Diabetes Mellitus (IDDM) have been associated with several risk factors, particularly the degree of metabolic control and evolution time of the disease. A study was conducted with 219 randomly selected patients with IDDM at our clinic; evolutive, clinical and analytical parameters were assessed and conventional or multiple insulin therapy was evaluated. The classification of glycated hemoglobin (Hb A1c) in quartiles demonstrated a relatively higher incidence of diabetic retinopathy and nephropathy in the upper quartiles versus the lower quartile (p < 0.05). Likewise, patients with multiple insulin therapy had lower retinopathy (24.5% vs. 50.6, p < 0.001) and nephropathy rates (12.9% vs. 26.6%, p < 0.05) compared with those following a conventional insulin therapy. The multivariate analysis showed a statistically significant regression model (p < 0.001) for microalbuminuria level in patients with no established nephropathy; in these patients, the evolution time of IDDM and their Hb A1c level showed a positive independent association, and the use of multiple insulin therapy was a protective factor. The regression analysis of microalbuminuria levels compared with glycated hemoglobin in patients with no established nephropathy showed a value for Hb A1c of 9% as a break-point; from this point upwards microalbuminuria levels increased more markedly. The multivariate analysis here presented can help identify the presence of microalbuminuria in the pathological range in patients with IDDM followed at a hospital clinic from feasible clinical variables (evolution time, glycated hemoglobin level, program of insulin therapy used) establishing a metabolic objective which helps prevent the development of this complication.
Time series analysis is a statistical procedure appropriate for repeated observations on a single subject or unit. The goal of the analysis may be to determine the nature of the process that describes an observed behavior or to evaluate the effects of a treatment or intervention. Model identification involves specifying which of several alternative Autoregressive Integrated Moving Average (ARIMA) models best describes the series and may be used to investigate basic processes. This is illustrated by an example involving selecting the model of nicotine regulation that best represents smokers. Intervention analysis involves determining if there are any changes in level or direction for the series as a result of the intervention. Two types of applications have potential for the substance abuse area: (1) evaluation of the effects of an intervention on a single individual, and (2) evaluation of organizational-level changes (i.e., program evaluation). This is illustrated by an example that examines the effect of relaxation therapy on blood pressure. Pooled time series procedures are employed to combine the data from several different individuals or units, either by cross-sectional analysis or meta-analysis. In addition, several other issues are discussed that are critical to performing a time series analysis: selection of an appropriate computer program, alternative procedures for handling missing data, procedures for multiple observations at each occasion, and corrections for seasonal data.
A simplified method for the in vitro determination of TIBC and UIBC in serum using 59Fe was subjected to quality control in the laboratory and clinically studied in duplicate determinations of 185 sera of an unselected patient population. The data obtained were investigated by statistical means (regression, correlation, variance analysis). The precision of the method was evaluated step by step. The results indicate that the radiochemical determination of TIBC values is equivalent to the "indirect" one (UIBC + SI) as far as accuracy is concerned. Advantages of the radiochemical method are discussed.
Hypertension in the elderly features differently from its younger counterpart in terms of diagnosis, associated condition, atypical manifestation, management and complication. Epidemiological study in this increasing age group in the community is, therefore, needed. 334 elderly subjects living in various parts of Bangkok were randomly recruited by appointment at 7 geriatric day centers situated in local health offices of Bangkok Metropolitan Authority. Each subject received blood tests before being interviewed and measured by digital sphygmomanometer. Blood pressure and heart rate changes were recorded during lying, sitting and standing. The prevalence of hypertension was 36.5 per cent, 33.2 per cent were already aware of its existence while 3.3 per cent were newly detected by the survey. Isolated systolic hypertension, a unique subtype found in the elderly, was 4.5 per cent of all or 37.5 per cent among the hypertensive group. The associated medical conditions among the case group were diabetes mellitus 22.9 per cent, hyperlipidemia 13.9 per cent, hyperuricemia 33.3 per cent and heart disease 18.0 per cent. As far as postural hypotension is concerned, 14.8 per cent of case group whereas 11.3 per cent of the control group were affected. On the other hand, the symptom of postural dizziness was found to be 31.1 per cent and 55.2 per cent in the case and control group respectively. Following the statistical logistic regression analysis, the independent associated factors in the hypertension group were: history of hyperlipidemia, increased serum uric acid and poor heart rate response after standing. These findings, as parts of the multiple pathology and potential complications prevalent among this group, should be of concern by any physician looking after the elderly.
Fibrates are a standard in the treatment impaired lipid metabolism, in particular in combined disorders. The classical Helsinki trial provided evidence of a decreased incidence of IHD in the treated group as compared with the group on placebo. Moreover there is some recent work which proved by statistical methods regression of atherosclerosis after fibrate administration, e.g. the angiographic study BECAIT with bezafibrate. The objective of the present study was to test the effectiveness of bezafibrate (Regadrin B, 200 mg tablets, Berlin-Chemie, FRG) in patients with combined familial hyperlipidaemia. The total cholesterol concentration dropped by 12.7% the LDL-cholesterol concentration by 8.8%. There was a significant drop of triacylglycerols by 37% and a rise of HDL-cholesterol by 24.2%. The apoB concentration declined by 11.3% and apo A-1 increased by 19.6%. The fibrinogen value dropped significantly by 15.2%, the Lp(a) value did not change significantly. The body weight in the two groups did not change significantly. The achieved results resemble those of work published abroad. In the authors opinion it is a positive feature that it proved possible to engage the patients in regular aerobic physical activity. Bezafibrate, Regadrin B was well tolerated by the patients, neither clinical nor laboratory tests revealed significant undesirable effects.
OBJECTIVE: To develop and validate a population pharmacokinetic model for gentamicin in horses, using retrospective clinical data. ANIMALS: 62 horses that had been treated IV with multiple doses of gentamicin at our veterinary teaching hospital between 1987 and 1996. Procedure-46 horses were assigned to the study group, and 16 to the validation group. Detailed history of dosage, sample collection times, and selected pathophysiologic variables were recorded for each patient. Samples were analyzed by use of a fluorescence polarization immunoassay method. Pharmacostatistical analysis was conducted, using computer software. The predictive model correlates pharmacokinetic parameters to concomitant pathophysiologic variables and estimates the inter- and intraindividual variability in disposition. RESULTS: A two-compartment model best described the data. Clearance (CI) was linearly correlated to body weight and serum creatinine concentration. Volume of the central compartment (Vd(c)) was linearly related to body weight. Interindividual coefficients of variability for CI and Vd(c) were 24 and 16%, respectively. The residual variability (intraindividual) was 13%; mean prediction error percent (bias) was 2%; and mean absolute prediction error percent (precision) was 29%. CONCLUSIONS: Population pharmacokinetic analysis allows study of the basic features of gentamicin disposition in horses with sparse data per individual. A considerable proportion of the pharmacokinetic variability of gentamicin in our study population was explained by differences in body weight and serum creatinine concentration. CLINICAL RELEVANCE: Population pharmacokinetics can be used to design first-dosage regimens according to the clinical characteristics of individual animals. Population pharmacokinetic models could also be included in Bayesian forecasting strategies to improve plasma concentration predictions in individual patients.
This paper describes a system written to carry out regression analyses under certain generalized linear models that are widely used in biomedical research. These include continuous response models such as the Weibull, log-logistic, log-normal and Cox proportional hazards models used in survival analysis, and also discrete Poisson, binomial and multinomial response regression models. The system fits models, generates residuals and other diagnostic output, and has an all-subsets regression feature. This paper describes the models implemented and gives statistical background; Part II describes the ISMOD system and presents examples of its application.
A failure analysis of interference screw fixation was performed to test the hypothesis that bovine and/or elderly human cadavers are appropriate models for bone-patellar tendon-bone anterior cruciate ligament (ACL) reconstruction fixation studies. Failure mode is an important criterion for validating experimental models. The bovine, young human, and elderly human failure loads were 799 +/- 261 N, 655 +/- 186 N, and 382 +/- 118 N, respectively, and the failure modes were 75%, 69%, and 30% tissue failures, respectively. The similarities between the bovine and young human models in failure loads and failure modes indicate that bovine models are appropriate for ACL reconstruction fixation studies. The statistically significant differences between the young human and elderly human models in failure loads and failure modes indicate that elderly human cadavers are not an appropriate model for ACL reconstruction fixation studies. The differences in failure modes are consistent with previous studies using elderly human cadavers in which the predominant failure mode was bone block pullout. The tissue failures observed in the bovine and young human models contradict previous studies suggesting fixation strength is the weakest link in bone-patellar tendon-bone ACL reconstruction. Results of linear regression modeling showed statistically significant correlations between insertion torque and failure load (R2 = 0.44, P < 0.0001) and interference (defined as the screw outer thread diameter minus the tunnel-bone block gap) and insertion torque (R2 = 0.18, P = 0.003) when data from all models was combined. Results for the bovine model multiple regression showed a statistically significant regression of insertion torque (linear) and interference (quadritic) versus failure load (R2 = 0.56, P = 0.02). Regression slopes for screw diameter (P = 0.52) and gap size (P = 1.00) were not statistically significant. These results indicate that insertion torque and interference are independent predictors of failure load and should be included in future interference screw studies in addition to bone block dimensions, tunnel size, gap size, and screw diameter. Clinicians may consider using insertion torque and interference as indicators of postoperative graft fixation regarding rehabilitation decisions.
A simple test for goodness of fit of the proportional hazards regression model has recently been proposed. This article indicates how a large number of programs in current use to fit this model can be easily adapted to incorporate this goodness of fit statistic.
Suppose we use generalized estimating equations to estimate a marginal regression model for repeated binary observations. There are no established summary statistics available for assessing the adequacy of the fitted model. In this paper we propose a goodness-of-fit test statistic which has an approximate chi-squared distribution when we have specified the model correctly. The proposed statistic can be viewed as an extension of the Hosmer and Lemeshow goodness-of-fit statistic for ordinary logistic regression to marginal regression models for repeated binary responses. We illustrate the methods using data from a study of mental health service utilization by children. The repeated responses are a set of binary measures of service use. We fit a marginal logistic regression model to the data using generalized estimating equations, and we apply the proposed goodness-of-fit statistic to assess the adequacy of the fitted model.
Parametric models for interval censored data can now easily be fitted with minimal programming in certain standard statistical software packages. Regression equations can be introduced, both for the location and for the dispersion parameters. Finite mixture models can also be fitted, with a point mass on right (or left) censored observations, to allow for individuals who cannot have the event (or already have it). This mixing probability can also be allowed to follow a regression equation. Here, models based on nine different distributions are compared for three examples of heavily censored data as well as a set of simulated data. We find that, for parametric models, interval censoring can often be ignored and that the density, at centres of intervals, can be used instead in the likelihood function, although the approximation is not always reliable. In the context of heavily interval censored data, the conclusions from parametric models are remarkably robust with changing distributional assumptions and generally more informative than the corresponding non-parametric models.
To evaluate more carefully the previously reported relation between myopia and dental caries, the refractive status and dental-caries experience of 196 high school students were evaluated. Statistical analysis was done by chi-square and computer-based multiple regression analysis. No statistically significant relation between the two conditions was found.
The activity of dimethylaminomethyl-10-hydroxycamptothecin (topotecan) was evaluated against a panel of xenografts derived from ependymomas (D528 EP, D612 EP), childhood high-grade gliomas (D-456 MG, D-212 MG), adult high-grade gliomas (D-245 MG, D-54 MG), and medulloblastomas (D425 Med) growing s.c. and i.c. (intracranially) in athymic nude mice. Topotecan was given at a dose of 1.9 mg/kg by i.p. injection in 0.9% saline using a volume of 90 ml/m2 on days 1-5 and 8-12, which represents the dose lethal to 10% of treated animals. Topotecan was active in the therapy of all s.c. xenografts tested, with growth delays ranging from 6.3 days in D-54 MG to 55.7 days in D528 EP. Topotecan produced statistically significant tumor regressions in D425 Med, D-456 MG, D-245 MG, D528 EP, and D612 EP. No tumor regression was seen in any control animal. Statistically significant increases in median survival were seen in the two i.c. xenografts--D-456 MG (28.6% increase) and D-54 MG (39% increase)--treated with topotecan. These studies suggest that topotecan may be an important new addition to the therapy of central nervous system tumors.
The most basic task in subaperture stitching test work is to confirm the precision of the system. We propose a method with which to calculate the system's precision. Statistical theory, especially regressive analysis, is employed. To discuss the statistical characteristics of all the random variables is the objective of the precision analyses. The results show that the number of sample points and the connatural error of the interferometer are the most important factors in the analyses.