Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Statistical Regression”

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.

At least 613 records · Page 34Linked to original sources
PubMed2001

[Methods of analysis and prognostication of a number of indicators in tuberculosis].

The paper proposes procedures for analyzing and predicting the rates of total morbidity due to tuberculosis and the time of its cure. Original procedures for identifying the factors that most substantially influence total tuberculosis morbidity rates (incidence rates) are described. A statistically significant regression equation was derived to predict tuberculosis morbidity in the cities and towns of the Rostov region (the determination rate R2 = 0.95; the mean weighed predictive error is no more than 5%, with 1-2% in the cities). A total approach to statistical assessment of the impact of concomitant diseases on the clinical recovery rates is proposed. Estimates indicated that there is alpha negative statistically significant correlation between the rapidity of recovery and the presence of concomitant pathology (alcoholism). A statistical correlation between the indices of regression of active tuberculosis was assessed. In 96% of cases, transition of active tuberculosis to inactive one can be judged from the values of only two factors. A functional relationship has been derived, which defines the onset of the phase of inactive tuberculosis with accuracy sufficient for practical purposes.

Forecasting↗
PubMed1983

Blood pressure reductions: correcting for regression to the mean.

Reductions in high blood pressure (BP) from participating in screening and treatment programs are often assessed by comparing BP measurements before and after participation. The interpretation of such changes in measured blood pressure is confounded by the tendency of high pressures to decline as a result of a statistical artifact--regression to the mean. The problem arises whenever baseline measurements are used both for selection of participants and for comparisons with pressures obtained later. We developed a statistical model which predicts the average decline due to regression for participants in a screening or treatment program. This regression effect must be subtracted from the observed reduction in BP (the difference between baseline and later measurements) to obtain the average net reduction in BP from the program. The regression effect is estimated as the product of two factors. The first factor is the proportion of the variance in the baseline (preprogram) measurement due to measurement error and the short-term variation (e.g., 0.24 for two replications averaged). The second factor is the difference between the mean baseline pressure of full participants and that of the underlying population of potential participants. The model was first illustrated with successive BP measurements from community screening programs, where the "program" was only remeasurement. The mean observed decline in diastolic BP between screens for 145 persons with elevated baseline BP was 7 mm Hg. After adjustment for regression to the mean, the net decline between screens was estimated to be 2 mm Hg. This decline is apparently due to the pressor effect, or stress of screening, and agrees with findings from other studies. Next the model was applied to the treatment phase of the Hypertension Detection and Follow-up Program. Overall, net reductions predicted by the model agree with those from independent measurements to within 0.1 mm Hg. The findings indicate the one can compute net reductions in BP from before-and-after comparisons in screening and treatment programs with reasonable accuracy, and these net reductions are generally much smaller than the crude BP declines.

Adult↗
PubMed2005

A practical longitudinal model for evaluating growth in Gelbvieh cattle.

Genetic evaluation of growth in Gelbvieh beef cattle was examined by multiple-trait (MTM) and random regression (RRM) analysis. The data set comprised 541,108 animals with 1,120,086 records. Approximately 15% of the animals in the data set had at least one record measured outside of the accepted MTM age ranges for weaning weight (Wwt) and yearling weight (Ywt). Fourteen percent of Wwt records and 19% of Ywt records were measured outside the accepted ranges for MTM analysis, and thus were excluded from MTM evaluations. Two RRM evaluations were performed using cubic Legendre polynomials (RRML) and linear splines (RRMS) with three knots at 1, 205, and 365 d of age. Data Set 1 (d1) utilized all available records, whereas Data Set 2 (d2) included only records measured within MTM ranges (1 d, 160 to 250 d, and 320 to 410 d). The RRML models did not reach convergence until diagonalization was imposed. After diagonalization, it was found that all longitudinal models required fewer iterations to converge than the MTM. Correlations between the MTM, RRML-d2, and RRMS-d2 evaluations were >or=0.99 for all three traits, indicating that these models were equivalent when predicting breeding values from data within the MTM age ranges. Correlations between MTM, RRML-d1, and RRMS-d1 were >0.99 for Bwt and >0.95 for Wwt and Ywt. The lower correlations for Wwt and Ywt indicate that the added information does affect breeding value prediction. The RRM has the capability to incorporate records measured at all ages into genetic evaluations at a computing cost similar to the MTM.

Algorithms↗
PubMed2005

Studies on multiple trait and random regression models for genetic evaluation of beef cattle for growth.

A simulation study examined issues important for genetic evaluation of growth in beef cattle by random regression models with cubic Legendre polynomials (RRML) and linear splines with three knots (RRMS) compared with multiple-trait models (MTM). Parameters for RRML were obtained by conversion from covariance functions. Parameters for MTM and RRMS were extracted from RRML at 1, 205, and 365 d; parameters for RRMS were the same as MTM for all effects except the permanent environment and the residual. Four data sets were generated assuming RRML included records at 1, 205, and 365 d; at 1, 160 to 250, and 320 to 410 d; at 1, 100, 205, 300, and 365 d; and at 1, 55 to 145, 160 to 250, 275 to 325, and 320 to 410 d. Accuracies were computed as correlations between the true (simulated) and predicted breeding values. With the first data set, excellent agreement in accuracy was obtained for all models. With the second data set, the accuracy of MTM dropped by up to 1.5% compared with the first data set, but accuracy was unchanged for both RRML and RRMS. With the third (fourth) data set, accuracies of RRML were up to 2.4% (2.5%) higher than with the first (second) data set. Small differences in accuracy between RRML and RRMS were found with the third and fourth data sets, which were traced to inflated correlations especially between 1 and 205 d in RRMS; inflation could be decreased by adding one extra knot at 100 d to RRMS. Diagonalization of random coefficients was crucial for RRML but not for RRMS, resulting in approximately six (two) times faster convergence with RRML (RRMS). Reduction of dimensionality in RRML associated with small eigenvalues caused a less accurate evaluation for birth weight. Genetic evaluation of growth by RRM requires careful implementation. The RRMS is simpler to implement than the RRML.

Age Factors↗
PubMed1997

Body fat percentage of children varies according to their diet composition.

OBJECTIVE: To ascertain the association between diet composition and body fat percentage in 9- and 10-year-old children. Also, to examine the influence of gender, total energy intake, fitness, physical activity, and parental body mass on the relationship between diet composition and adiposity. DESIGN: Diet composition was assessed using the National Cancer Institute food frequency questionnaire, and adiposity was measured using the average of results determined using two skinfold equations. Fitness levels and physical activity were ascertained using the 1-mile run/walk test and a self-report 15-item scale, respectively. SUBJECTS: A sample of 262 children (162 boys and 100 girls, mean age = 9.8 +/- 0.5 years) participated. STATISTICAL ANALYSIS: Regression analysis was used to determine the extent to which diet composition contributed to adiposity without statistical control for any potentially confounding variables. Partial correlations were calculated to assess the relationship between macronutrient intake and adiposity after potential confounders (gender, total energy intake, physical fitness, and parental body mass) were controlled statistically. RESULTS: Energy intake was positively related to adiposity. Fat intake, calculated as a percentage of total energy, was also positively related to adiposity, before and after control for potential confounding variables. Percentage of energy derived from carbohydrate was inversely related to adiposity, before and after controlling for potential confounders. APPLICATIONS: These findings indicate that the macronutrient intake of children, particularly dietary fat and carbohydrate intake, may play a role in adiposity, independent of the influence of total energy intake, gender, physical fitness, and parental body mass index.

Adipose Tissue↗
PubMed2005

HbA1c: a comparison of NGSP with IFCC transformed values.

BACKGROUND: An approved IFCC reference method for measuring HbA1c, with a firm and reproducible correlation with NGSP values, is now available. We established (i) the degree of agreement of HbA1c results between the NGSP-certified and the IFCC-calibrated (converted to NGSP values) immunochemical method and (ii) the difference in the classification of control of diabetes mellitus (DM) in individual patients between the methods. METHODS: HbA1c was measured on the same hemolysate from each patient by both methods (n=92). Results were analyzed by the kappa statistic, linear regression, and McNemar's chi(2) test. RESULTS: Both methods achieved acceptable analytical performance. The kappa statistic measure of agreement was 0.65 and r(2)=0.937. Overall, 21 (22.8%) patients were classified differently in the extent of diabetes control (good, acceptable, or poor), with a significant difference between the 2 methods (p<0.0005). CONCLUSIONS: The IFCC converted to NGSP values were significantly different from the previously used NGSP-certified method. The differences between the 2 methods are of sufficient magnitude that HbA1c results from these methods are not interchangeable. The IFCC method being scientifically superior in concept and design should replace the NGSP method. New HbA1c targets for DM management need to be established for the IFCC method.

Blood Chemical Analysis↗
PubMed2002

Does lamotrigine influence valproate concentrations?

The aim of this study is to investigate the effect of lamotrigine (LTG) on valproate (VPA) concentrations dependent on LTG dose, LTG concentration, and additional enzyme-inducing antiepileptic drugs (AED) as well. For this purpose the following patient groups were compared: VPA monotherapy, VPA + one enzyme-inducing AED, VPA + LTG, and VPA + LTG + one enzyme-inducing AED. A total of 400 serum concentrations from 372 patients were evaluated. Two or more serum samples from the same patient were considered only if the comedication had been changed. For statistical evaluation, regression analytical methods and an analysis of variance were performed. For the analysis of variance, the VPA serum concentration in relation to VPA dose:body weight (level:dose ratio, LDR) was calculated and compared for different drug combinations. The analysis of variance revealed a significant effect of enzyme-inducing comedication (as expected) and age on the VPA LDR. Patients on LTG had a slightly lower VPA LDR, but this effect was not statistically significant. In addition, nonlinear regression analysis confirmed that patients on enzyme-inducing AED (carbamazepine, phenytoin, phenobarbital, methsuximide) had significantly lower VPA concentrations. Patients on ethosuximide had slightly but not significantly lower VPA concentrations. Patients on LTG also had significantly lower VPA levels, but this effect was only minor (-7%) and most probably not of any clinical relevance. Furthermore, the regression analysis showed that the relationship between the VPA dose per body weight and the serum concentration deviates significantly from linearity. Children less than 6 years old had lower VPA levels than older children and adults on a comparable VPA dose per body weight. Gender had no significant influence on VPA serum concentration. In addition, a subgroup of 40 patients was analyzed to see whether changing the LTG dose influences VPA serum concentrations. It did not. Thus, the authors conclude that the effect of LTG on VPA concentrations is not of clinical relevance.

Adolescent↗
PubMed1998

Response during radiotherapy may be associated with outcome in mediastinal Hodgkin's disease.

A relationship between the rate of regression of lymphomas treated with chemotherapy and long-term outcome has been observed. This study was undertaken to determine if the rate of tumor regression during radiotherapy for mediastinal Hodgkin's disease is a predictor of in-field recurrence. Twenty-nine patients with early-stage Hodgkin's disease treated with radiotherapy alone as part of an NCI randomized trial had both a non-massive mediastinal component of disease and all requisite simulation and port films available for analysis. The histology was nodular sclerosis in all patients. Stage distribution was as follows: IA-1; IIA-17; IIB-8; IIIA1-3. The median age was 27 years and the median radiation dose was 4470 cGy. A mediastinal mass ratio was calculated from each patient's simulation and weekly port films by dividing the width of the mediastinal mass by the intrathoracic diameter at the level of the carina. Histopathologic correlation was also done to quantify the degree of tumor vs. sclerosis in the specimens. Univariate analysis and Cox proportional hazards analysis were used to study the association between several covariates (stage, sex, symptoms, extra-lymphatic disease, initial mediastinal mass ratio, age, dose, percent tumor in the specimen, and cumulative percentage of tumor regression) and time to in-field recurrence, as well as probability of any failure. Univariate analysis indicates that lower dose, higher percent tumor in the specimen, and lower cumulative percent regression are statistically significant predictors for in-field recurrence, as well as for any failure. By Cox regression analysis, cumulative percent regression is the sole factor independently associated with in-field recurrence (two-tailed P=0.04). The percent tumor in the specimen is the only factor similarly identified for time to any failure (two-tailed P=0.02). Histopathologic correlation suggests that patients with early stage mediastinal Hodgkin's disease who demonstrate a high percent tumor in the specimen may be at increased risk of failure. Patients with a low cumulative percent regression during radiotherapy appear to be at an increased risk of in-field recurrence.

Adolescent↗
PubMed1991

Effect of airway inertance on linear regression estimates of resistance and compliance in mechanically ventilated infants: a computer model study.

Respiratory inertance (I) is usually ignored when resistance (R) and compliance (C) of mechanically ventilated infants are estimated by least squares linear regression. Values of I that have been reported for these patients can cause impedances whose magnitudes approximate respiratory resistance. We show theoretically that if inertance is neglected no error is expected in resistance estimates, but a positive bias in compliance can be, proportional to the inertance, the compliance, and the sinusoidal frequency at which the measurements are made. To determine the errors in parameter estimates when the pressure waveform is non-sinusoidal, we simulated linear regression based on non-inertive and inertive models. R, C, and I of the simulated lung were varied over the range expected in an infant intensive care unit. The ventilator was simulated as a critically damped second order system with a square pulse input. The rise time (TR) of the pressure pulse was varied over the range reported in infant ICUs. Simulated measurements confirmed that resistance is correctly estimated if inertance is neglected. Maximum error in compliance estimates (13%) occurred when TR and R were low, and C and I were high. The variation in the error in estimated compliance was consistent with the theory. Coefficients of variation of the parameters, the standard errors, and R2 of the regressions tended to deteriorate with increasing compliance error, but the relationships were not single valued. These statistics may alert investigators to possible bias in compliance caused by neglected inertance, but cannot be used to correct any bias.

Airway Resistance↗
PubMed1975

Applications of statistics in clinical chemistry. A critical evaluation of regression lines.

When two chemical determination methods are compared, a regression line is commonly used to elucidate constant and proportional errors. The classical procedure for the calculation of such a line is compared to the fairly unknown procedures described by Deming and by Bartlett. It is shown that the reliability of the classical procedure is restricted to only some cases. Deming's procedure is more generally applicable and also has the advantage, that estimates are obtained for the random errors in both chemical determination methods. Bartlett's procedure is not recommended.

Chemistry, Clinical↗
PubMed2005

Non protein bound iron concentrations in amniotic fluid.

OBJECTIVES: To investigate whether amniotic fluid concentrations of non protein bound iron (NPBI) vary with growth in healthy fetuses and also offer a reference curve in the second trimester of pregnancy. DESIGN AND METHODS: Amniotic fluid concentrations of NPBI were measured by HPLC in 118 women with physiological singleton pregnancies, who underwent amniocentesis for fetal karyotype between weeks 15 and 18 of gestation. RESULTS: NPBI increased progressively from weeks 14--15 to weeks 15--16, peaking at 17--18 weeks of gestation. NPBI values regressed positively with gestational age (GA). Multiple linear regression analysis between NPBI, as dependent variable, and various fetal parameters, as independent variables, showed a statistically significant regression coefficient with GA, bi-parietal diameter and transverse cerebellar diameter. CONCLUSIONS: The present data constitutes the first quantification of NPBI concentrations in amniotic fluid under physiological conditions. Correlations with GA and ultrasound fetal biometry suggest that NPBI may play a role in fetal growth.

Adult↗
PubMed1998

Relationship between % heart rate reserve and % VO2 reserve in treadmill exercise.

For exercise prescription purposes, it is often assumed that % heart rate reserve (%HRR) provides equivalent intensities to %VO2max. However, a recent study from this laboratory demonstrated that during cycling exercise %HRR is not equivalent to %VO2max, but is instead equivalent to a percentage of the difference between resting and maximal VO2, i.e., % VO2reserve (%VO2R). The current study examined these relationships during treadmill exercise. Fifty adults performed Bruce protocol treadmill tests to exhaustion. For each subject, data obtained at rest, at the end of each stage, and at maximum were used to determine linear regressions of %HRR versus %VO2max, and of %HRR versus %VO2R. For %HRR versus %VO2max the mean intercept and slope were -6.1+/-0.7 and 1.10+/-0.01, respectively, with a mean r of 0.990+/-0.002. For %HRR versus %VO2R, the mean intercept and slope were 1.5+/-0.6 and 1.03+/-0.01, respectively, with a mean r of 0.990+/-0.002. Both regressions differed statistically from the line of identity (i.e., intercept of 0 and slope of 1). However, the regression of %HRR versus %VO2R was significantly closer (P < 0.001 ) to the line of identity than was the regression of %HRR versus %VO2max. We conclude that %HRR should be considered as an indicator of %VO2R, not %VO2max, when prescribing treadmill exercise, as was previously concluded for cycling exercise.

Adolescent↗
PubMed2002

Evidence for trends in UK flooding.

Recent major flooding in the UK has raised concern that climate change is causing increases in flood frequency and flood magnitude. This paper considers whether UK flood data provide evidence of increasing trends in fluvial floods. The analysis examines both local and national flood series and investigates the effect of climate variability on trend detection. The results suggest that there have been trends towards more protracted high flows over the last 30-50 years, but that this could be accounted for as part of climatic variation rather than climate change. There is no statistical evidence of a long-term trend in flooding over the last 80-120 years. Thus, although climate change could be influencing floods, direct analysis of flood records does not yet provide proof.

Climate↗
PubMed2005

Relative focus map estimation using blind deconvolution.

An automatic focus map extraction method is presented that uses a modification of blind deconvolution for estimation of localized blurring functions. We use these local blurring functions [so-called point-spread functions (PSFs)] for extraction of focus areas on ordinary images. In this inverse task our goal is not image reconstruction but the estimation of localized PSFs and the relative focus map. Thus the method is less sensitive than general deconvolution is to noise and ill-posed deconvolution problems. The focus areas can be estimated without any knowledge of the shooting conditions or of the optical system used.

Algorithms↗