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PubMed2000

Methodology for estimating the abundance of rare animals: seabird nesting on north east Herald Cay.

We discuss the problem of estimating the number of nests of different species of seabirds on North East Herald Cay based on the data from a 1996 survey of quadrats along transects and data from similar past surveys. We consider three approaches based on different plausible models, namely a conditional negative binomial model that allows for additional zeroes in the data, a weighting approach (based on a heteroscedastic regression model), and a transform-both-sides regression approach. We find that the conditional negative binomial approach and a linear regression approach work well but that the transform-both-sides approach should not be used. We apply the conditional negative binomial and linear regression approaches with poststratification based on data quality and availability to estimate the number of frigatebird nests on North East Herald Cay.

Animals↗

PubMed1997

Quantitative description of migration behavior of porphyrins based on the dynamic complexation model in a nonaqueous capillary electrophoresis system.

The effect of an additive (Brij 35) on the mobilities of a group of porphyrin acids is quantitatively characterized based on a 1:1 dynamic complexation model. Varying additive concentration shifts the equilibrium and changes the viscosity of the background electrolyte. The equilibrium constant, the electrophoretic mobility of the free analyte, and the electrophoretic mobility of the complex are identified as the parameters necessary to describe the analytes' migration behavior. Several statistical methods for obtaining these parameters are discussed. The equilibrium constants and complex mobilities are calculated using three different linear regression methods. The weighted y-reciprocal method was preferred because it gives smaller error, and the data points are evenly distributed along the concentration axis. These values are confirmed using a nonlinear regression to ensure that the proper weighting was used in the linear regression plots. The parameters are then used to predict the apparent mobilities of the analytes over the entire additive concentration range, allowing the optimum separation conditions to be identified. For disc-like molecules, such as porphyrins, the mobility is determined by the orientation of the molecule in an electric field, in addition to their size and charge. The strength of binding between the porphyrins and Brij 35 depends on the number of binding sites and the solvation shell.

Buffers↗

PubMed1998

Bronchial responsiveness and five-year FEV1 decline: a study in miners and nonminers.

Increased nonspecific bronchial responsiveness (NSBR) may be a risk factor for the development of chronic airflow obstruction. We evaluated this hypothesis in a cohort of 378 underground coal miners and working nonminers. Methacholine testing was performed at the beginning and end of a 5-yr study period. Spirometry was repeated at 6-mo intervals and individual 5-yr FEV1 slopes were calculated by linear regression. Relationships between FEV1 slopes and NSBR were examined using multiple linear regression models, controlling for FEV1 level, smoking, and mining. Increasing NSBR at the initial survey was associated with a somewhat greater rate of subsequent FEV1 decline. Methacholine responders at the final survey had a considerably increased rate of decline during the previous years. Responsiveness status changed over the 5 yr in 22% of the subjects. Both the development and persistence of increased NSBR were strongly associated with higher rates of FEV1 decline. In contrast, FEV1 declines were not accelerated among workers with increased NSBR that reverted to normal. Smoking and mining were both independently associated with FEV1 declines, but did not substantially modify the effect of NSBR. Due to its variability over time, NSBR testing predicts lung function decline only in some individuals, and its value as a prognostic test for chronic airway disorders is limited. Because improvement in bronchial hyperresponsiveness was associated with a reduction in the rate of FEV1 loss, interventions directed at preventing or reducing nonspecific airway hyperresponsiveness should be investigated.

Adult↗

PubMed2005

The correlation between height of macular detachment and visual outcome in macula-off retinal detachments of < or = 7 days' duration.

OBJECTIVE: To determine the relationship between the height of macular detachment and visual recovery after treatment of macula-off retinal detachments (RDs) of < or = 7 days' duration. DESIGN: Prospective comparative case series. PARTICIPANTS: Fifty-two eyes of 52 consecutive patients who presented to one institution with macula-off RDs of < or = 7 days' duration were prospectively enrolled in the study. METHODS: Gender, age, lens status, duration of macular detachment, and presenting visual acuity (VA) were recorded for all patients. Each patient underwent a 3-dimensional B-scan ultrasound examination at the time of presentation. The height of macular detachment was calculated using the mean measured distance between the retinal pigment epithelium and the outer neurosensory retina 3, 4, and 5 mm temporal to the center of the optic nerve head. All patients underwent primarily successful reattachment surgery within 7 days of macular detachment. Final vision was recorded with a minimum of 6 months' follow-up. MAIN OUTCOME MEASURE: Postoperative VA evaluated as a continuous variable. RESULTS: For the 52 subjects, a direct correlation between lower height of macular detachment and better final postoperative vision (dependent variable) was observed with linear regression (slope, 0.114; 95% confidence interval, 0.022-0.206; P = 0.016). Multivariate linear regression analysis with a backward stepwise approach did not demonstrate any significant association between postoperative vision and predictor variables (gender, age, lens status, duration of macular detachment, macular height, and preoperative vision), except for macular height. CONCLUSION: Lower height of macular detachment correlates with better visual recovery after treatment of macula-off RDs of < or = 7 days' duration.

Adolescent↗

PubMed2001

Phase-feeding supports maximum growth performance of broiler chicks from forty-three to seventy-one days of age.

Phase-feeding (PF) was tested to evaluate its efficacy compared with NRC recommendations for broilers. Two modified PF regimens were also tested that involved lowering amino acid requirements predicted by PF linear regression equations by 10% (PF10) and increasing the slope of the linear regression equations by 15% (PF15). Experimental diets were fed from 43 to 71 d. Broilers fed the NRC regimen were given a single diet throughout the experiment, whereas PF, PF10, and PF15 were tested with a series of four diets (43 to 50 d, 50 to 57 d, 57 to 64 d, and 64 to 71 d). At 71 d, no differences (P < 0.05) in weight gain, feed intake, or feed efficiency were observed among treatments. Intake of crude protein, digestible lysine, sulfur amino acids (SAA), and threonine were decreased (P < 0.05) by PF, PF10, and PF15 relative to that of broilers fed the NRC diet. Gain per unit digestible lysine and threonine intake were increased (P < 0.05) by PF, PF10, and PF15, and gain per unit digestible SAA intake was increased (P < 0.05) by PF10 and PF15 relative to broilers fed the NRC diet. No differences (P > 0.05) were observed in carcass, breast, wing, or leg yield, but abdominal fat was increased (P < 0.05) by the PF10 regimen relative to that of broilers fed the NRC diet. Economic analysis indicated that PF and PF10 may lower the cost of feed consumed and the cost per unit weight gain or breast yield relative to broilers fed the NRC diet.

Amino Acids, Sulfur↗

PubMed2003

Regression models for linkage: issues of traits, covariates, heterogeneity, and interaction.

Regression methods offer a common framework to analyze linkage for quantitative trait loci as well as linkage for affection status using affected sib-pairs. Although numerous papers on regression methods for linkage have been published, some common themes and important caveats tend to be scattered across the literature. For example, the typical approach is to regress a function of traits on identical-by-descent (IBD) information, but the reversal (regression of IBD on a function of traits) offers important insights. A second example is the use of regression equations to assess linkage heterogeneity or gene-environment interaction, and why these two different etiologies are difficult to distinguish with affected sib-pair data. A third example has to do with the differences, and similarities, between linear regression and non-linear regression methods for affected sib-pair data. The purposes of this paper are to review some recent developments in the linkage regression framework, to emphasize strengths and weaknesses of various proposed methods, and to highlight some important assumptions and caveats.

Data Interpretation, Statistical↗

PubMed2001

Relationships of sire predicted transmitting ability for somatic cell score with measures of daughter performance.

The relationship between sire predicted transmitting ability (PTA) for somatic cell score (SCS) and occurrence of mastitis in daughters was characterized with 304 Holsteins first freshening since 1991 in the Virginia Tech dairy herd. No direct sire selection for PTA SCS was practiced in the herd. Linear regressions of first lactation average SCS (1.3), number of cases of mastitis (0.80), days clinical (7.0), and number of treatments for mastitis (2.0) on PTA SCS were significant. Linear regression coefficients for second and third lactations were generally positive, but like quadratic and cubic coefficients in this study, were not significant. Relationship of sire PTA SCS and measures of lifetime (84 mo opportunity) performance were determined for 2,494,195 Holsteins born between 1979 and 1987. Linear coefficients from regression on PTA SCS for number of lactations (-0.31), days of productive life (-87.0), total days in milk (-72.2), lifetime milk (-1609.1), fat (-80.7), and protein (-48.2) production, relative net income adjusted for opportunity cost for fluid markets (+13.47), first lactation average SCS (+1.00), and first lactation mature equivalent milk (+429.9) were different from zero. Partial regressions holding PTA milk or PTA protein constant were substantially larger than linear coefficients. When PTA productive life was held constant, the relationship between PTA SCS and measures of herd life and lifetime yield became positive, and relative net income adjusted for opportunity cost variables became moderately positive. One of the major expenses associated with higher susceptibility (higher PTA SCS) may be shorter herd life.

Animals↗

PubMed2001

Predicting dental treatment workload of U.S. military personnel.

As the demographic composition of the U.S. armed forces shifts, so does dental treatment workload (DTW). To date, the effects of such shifts on DTW have been speculative. This study seeks to build regression models to predict the DTW of recruit and active duty military personnel as service demographic factors shift. The data come from a 1994-1995 random sample of 13,050 active duty and 2,711 recruit personnel. Dental treatment needs were charted for all participants. Patient demographic variables--age, sex, race, education, branch of service, and annual dental utilization (for all); home region and marital status (recruits only); and rank (active duty only)--were noted. Treatment needs were converted to composite time values. Respondent demographic factors were regressed on composite time values to determine which factors influence DTW using backward, stepwise, linear regression. Results show that DTW varies across demographic categories. The magnitude and direction of change in DTW as service demographic variables shift can be predicted with linear regression models.

Adolescent↗

PubMed2002

Independent representations of limb axis length and orientation in spinocerebellar response components.

Dorsal spinocerebellar tract (DSCT) neurons transmit sensory signals to the cerebellum that encode global hindlimb parameters, such as the hindlimb end-point position and its direction of movement. Here we use a population analysis approach to examine further the characteristics of DSCT neuronal responses during continuous movements of the hind foot. We used a robot to move the hind paw of anesthetized cats through the trajectories of a step or a figure-8 footpath in a parasagittal plane. Extracellular recordings from 82 cells converted to cycle histograms provided the basis for a principal-component analysis to determine the common features of the DSCT movement responses. Five principal components (PCs) accounted for about 80% of the total variance in the waveforms across units. The first two PCs accounted for about 60% of the variance and they were highly robust across samples. We examined the relationship between the responses and limb kinematic parameters by correlating the PC waveforms with waveforms of the joint angle and limb axis trajectories using multivariate linear regression models. Each PC waveform could be at least partly explained by a linear relationship to joint-angle trajectories, but except for the first PC, they required multiple angles. However, the limb axis parameters more closely related to both the first and second PC waveforms. In fact, linear regression models with limb axis length and orientation trajectories as predictors explained 94% of the variance in both PCs, and each was related to a particular linear combination of position and velocity. The first PC correlated with the limb axis orientation and orientation velocity trajectories, whereas second PC with the length and length velocity trajectories. These combinations were found to correspond to the dynamics of muscle spindle responses. The first two PCs were also most representative of the data set since about half the DSCT responses could be at least 85% accounted for by weighted linear combinations of these two PCs. Higher-order PCs were unrelated to limb axis trajectories and accounted instead for different dynamic components of the responses. The findings imply that an explicit and independent representation of the limb axis length and orientation may be present at the lowest levels of sensory processing in the spinal cord.

Anesthesia↗

PubMed2007

A novel QSPR model for predicting θ (lower critical solution temperature) in polymer solutions using molecular descriptors.

In this study, we present a new model that has been developed for the prediction of θ (lower critical solution temperature) using a database of 169 data points that include 12 polymers and 67 solvents. For the characterization of polymer and solvent molecules, a number of molecular descriptors (topological, physicochemical,steric and electronic) were examined. The best subset of descriptors was selected using the elimination selection-stepwise regression method. Multiple linear regression (MLR) served as the statistical tool to explore the potential correlation among the molecular descriptors and the experimental data. The prediction accuracy of the MLR model was tested using the leave-one-out cross validation procedure, validation through an external test set and the Y-randomization evaluation technique. The domain of applicability was finally determined to identify the reliable predictions.

Linear Models↗

PubMed1992

Auditing quality control procedures in a chemical pathology laboratory--a multiple regression analysis.

We undertook a retrospective analysis of the monthly test rejection rates and the monthly external quality assessment scheme performance indices for our laboratory's two automated analysers, and examined the association of these variables with measures of laboratory workload, manpower, staff training, instrument servicing, seasonal and temporal factors and changes of calibration, method and assigned internal quality control values. Using multiple linear regression and stepwise multiple linear regression, we found that test rejection rates differed significantly between instruments, and were highest on the instrument performing the widest variety and lowest volume of tests. On that instrument, rejection rates were significantly associated with the introduction of new staff and laboratory manpower levels, and also showed a highly significant trend upwards over the study period, independent of the effects of the other variables examined. External quality assessment scheme performance indices showed small trends over the study period. They were not related to the test rejection rates on either analyser but also showed a significant association with the introduction of new staff and a small but significant association with laboratory workload. We conclude that the training and introduction of new staff and decreased laboratory manpower levels may significantly increase the level of test rejection, and adherence to appropriate quality control protocols effectively maintains the quality of the laboratory's results, but may not be completely successful in filtering out the effects of some assignable causes of variation in test results. It is suggested that clinical laboratories use the statistical approach adopted here to identify factors which may be adversely affecting quality performance and running costs and to provide evidence that quality control procedures are both cost- and quality-effective.

Clinical Laboratory Techniques↗

PubMed1999

Respiratory symptoms and pulmonary function in coal miners: looking into the effects of simple pneumoconiosis.

BACKGROUND: Although severe impairment of pulmonary function is believed to occur commonly in complicated pneumoconiosis, the relationships of simple coal workers' pneumoconiosis (CWP) to pulmonary function and respiratory symptoms have remained under debate. The study aims to investigate if simple pneumoconiosis is associated with significant impairment of pulmonary function and increased risk of respiratory symptoms. METHODS: Spirometry and diffusing capacity were performed in 205 miners with simple CWP and 289 without X ray evidence of pneumoconiosis, who were selected from a large underground coal mine in China. A questionnaire on occupational history and respiratory symptoms including breathlessness, chronic cough, and phlegm was administered. The presence or absence of emphysema on their X-ray films was also evaluated. Logistic regression and multiple linear regression analysis were applied to estimate the independent effect of CWP on respiratory symptoms and parameters of pulmonary function. RESULTS: On the average, the miners with CWP had lower values of pulmonary function and higher prevalences of respiratory symptoms, and emphysema than did those without. The simple CWP was associated with increased risk of the respiratory symptoms after adjusting for age, smoking, and years underground. Regression analysis showed that the CWP had significantly independent effects on parameters of pulmonary function. Even when the effects of emphysema, respiratory symptoms indicating chronic bronchitis were taken into consideration, the significant relationship between CWP and decrements in FVC and diffusing capacity remained. CONCLUSION: The findings of this study are consistent with simple CWP being a contributor to significant decrements in pulmonary function, and to increased risk of respiratory symptoms.

Adult↗

PubMed1996

Validation and clinical application of a continuous P0.1 measurement using standard respiratory equipment.

The airway occlusion pressure, P0.1, is the negative airway pressure generated during the first 100 msec of an occluded inspiration. P0.1 is a parameter for the neuro-muscular activation of the respiratory system, which is an important determinant for the work of breathing. It has been shown to be a good predictor for successful weaning from mechanical ventilation. Standard P0.1 measurement techniques are based on a total occlusion of the inspiration for more than 100 msec. These measurements are technically complex and therefore not useful for clinical purposes. Furthermore, a significant breath-by-breath variability has been shown for P0.1, which is neglected by any single point measurement technique. Therefore, we have developed a continuous on-line measurement for breath-by-breath determination of P0.1 using the Siemens Servo 900C respirator. In triggered mechanical ventilation the delay time between the onset of the patient's inspiration and flow delivery from the respiratory is more than 100 msec for this respirator. During that time the inspiration is occluded. Therefore, the trigger effort was proposed to be a good estimate of P0.1. Based on this, we calculated P0.1 as follows: airway pressure (Paw) was registered at the endotracheal tube site of the respiratory tubing, digitized and acquired by a personal computer at 100 Hz. The recorder output of the Servo 900C was connected to the same computer, delivering the electronical signal for the inspiratory valve to open when the inspiratory effort has exceeded the trigger threshold, which needs a minimal delay time of 80 msec. Around 20 msec after this signal flow is delivered from the respirator. The computer runs an algorithm, which recognizes this signal and calculates P0.1 (Servo P0.1) as the slope of the pressure drop during this 100 msec. Paw tracings and the calculated P0.1 values were displayed on the computer screen and stored on disk. This method was validated by comparing it to the standard technique, using a Hans-Rudolph valve for inspiratory occlusion and calculating P0.1 from Paw tracings during the occluded inspiration. For validation we used a mechanical lung model which generated P0.1 values ranging between 1.1-10.3 mbar. For a given adjustment of the lung model two standard measurements (standard P0.1) were made and compared to the Servo P0.1. In a total of 21 measurements the mean Servo P0.1 was 4.9 +/- 2.9 mbar; the mean standard P0.1 was 4.3 +/- 2.5 mbar. The mean difference between Servo P0.1 and standard P0.1 was 0.6 +/- 0.6 mbar (range: -0.3-1.8 mbar). The regression equation for linear regression analysis was: Servo P0.1 = 1.15* standard P0.1-0.05. This correlation was significant (r = 0.99, p < 0.01). From these data we conclude that the described method for continuous P0.1 measurement provides reliable values with the advantage of a maneuver-free, breath-by-breath measurement technique. It thereby opens the possibility for monitoring the neuro-muscular activation of the respiratory system at the bedside, which is shown as an example for a patient during weaning from mechanical ventilation.

Adult↗

PubMed1997

QT corrected for heart rate and relation between QT and RR intervals in beagle dogs.

The beagle dog has been widely used in cardiovascular research, but the adequacy of QT prediction formulas in dogs over a wide range of RR intervals has not been evaluated sufficiently. We investigated the QT-RR relation in beagles by analysis of the QT and preceding RR intervals obtained from 24-h ambulatory electrocardiograms. The acceptability of 14 QT prediction formulas was evaluated by use of 100-150 selected pairs of QT-RR points per animal in seven male and seven female beagles. The accuracy of fit with the measured data was assessed according to the minimum Akaike information criterion. The best fit was given by the logarithmic and inverse Kovács' formulas among one- and two-parameter linear regression equations, respectively. Exponential formulas produced a better fit than did the linear regression formulas, but are impractical because of the complicated interpretation of parameters due to the nonlinearity. In addition, the results obtained under physiological conditions were also confirmed by those of the pharmacological intervention study with disopyramide. Consequently, we propose a one-parameter logarithmic formula (QTc= log600 x QT/logRR) for correcting the QT interval for a heart rate of 100 bpm and the inverse Kovács' formula for evaluating a reverse-use-dependency of QT prolongation.

Animals↗

PubMedDate not supplied

Lack of correlation among the 3 outcomes describing SLE: disease activity, damage and quality of life.

OBJECTIVE: The aim of the this study was to correlate three outcome measures in patients with SLE, namely disease activity, damage, and quality of life. METHODS: One hundred and five SLE patients completed the Medical Outcome Survey (MOS) SF-20 during their regular clinic visit. Disease activity (SLEDAI) and damage (SLICC/ACR Damage Index) were assessed according to a standard protocol. Statistical analyses included the Pearson correlation coefficients, a logistic regression, and a linear regression analysis. RESULTS: There was no correlation between the SLEDAI and SLICC/ACR DI. There was no correlation between the SLICC/ACR DI and any of the MOS domains by Pearson correlation. Although a statistical correlation was demonstrated between the SLEDAI score and the social functioning and health perception domains of the MOS SF-20, there were not clinically important. CONCLUSION: Thus, the three outcomes of disease activity, accumulated damage, and health status remain important independent outcome measures in the assessment of prognosis in patients with SLE.

Adolescent↗

PubMed2002

Prediction of human clearance from animal data and molecular structural parameters using multivariate regression analysis.

The aim of the study reported here was to develop a method for predicting human clearance that can be applied to various kinds of drugs using clearance values for rats and dogs and some molecular structural parameters. The clearance data for rats, dogs, and humans of 68 drugs were obtained from literature. The compounds have various structures, pharmacological activities, and pharmacokinetic characteristics. In addition, molecular weight, c log P, and the number of hydrogen bond acceptors were used as possible descriptors related to the human clearance value for each drug. Three types of regression methods, multiple linear regression (MLR) analysis, partial least squares (PLS) method, and artificial neural network (ANN), were used to predict human clearance, and their predictive performances were compared with allometric approaches, which have been widely used in interspecies scaling. In MLR and PLS analyses, interaction terms were introduced to evaluate the nonlinear relationships. For the data sets used in the present study, MLR and PLS with quadratic terms gave the same equation and the best predictive performance. The value of the squared cross-validated correlation coefficient (q(2)) was 0.682. In conclusion, the MLR method using animal clearance data from only two species and using easily calculated structural parameters can generally predict human clearance better than allometric methods. This approach can be applied to drugs with various characteristics.

Animals↗

PubMed1995

Static and fatigue failure properties of thoracic and lumbar vertebral bodies and their relation to regional density.

This study investigated (1) whether a characterization of the macroscopic architecture within the vertebral centrum would improve predictions of vertebral strength, (2) if regions in the centrum where least bone loss with age occurs are more predictive of vertebral strength, and (3) whether different patterns of the macroscopic architecture are predictive of static as compared to fatigue strength. To characterize the vertebral macroscopic architecture, a regional bone mineral density (rBMD) technique was used that estimated the cancellous density distribution (in 18 specific regions of the vertebral centrum) for vertebrae T7-L4, from spines of 20 female cadavers. Static and fatigue failure properties of whole vertebrae were obtained, and predictive models of static and fatigue failure properties of whole vertebrae were examined. We found that (1) vertebral failure properties were better predicted by combinations of vertebral regional cancellous density (multiple linear regressions) rather than by any individual region of cancellous density alone (simple linear regressions); (2) models using regions of density that demonstrated minimum decline with age [from the data of Flynn and Cody (Calcif. Tissue Int. 53, S170-S175 (1993))] resulted in better correlations with ex vivo vertebral static failure properties than models using density regions that showed maximum decline with age, and (3) static and fatigue characteristics required different density regions to reach significance. (A comparison of models predictive of static and fatigue failure properties revealed that anterior density regions were most often included in predictive models of the static properties while posterior regions were more predictive of the fatigue properties).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed2002

Pharmacodynamics of high-dose methotrexate in pediatric patients.

OBJECTIVE: To establish a relationship between the pharmacokinetics of high-dose methotrexate (MTX) and toxicity in children of a pediatric oncology department and to reassess MTX concentrations at which the patients would be at high risk for toxic effects. METHODS: This study included 37 patients (227 treatment courses) who received a median dose of 4.87 g/m(2) of MTX in a 4-hour infusion. The population pharmacokinetic parameters of MTX were estimated by parametric (IT2B) and nonparametric methods (NPEM). Gastrointestinal, renal, and hematologic toxicity were evaluated. The relationship between pharmacokinetic parameters and toxicity was analyzed by logistic regression and multiple linear regression. RESULTS: Equations to predict hematologic and nonhematologic toxicity were obtained. An increase of 100 micro mol/L in the MTX peak concentration meant a 12% (p = 0.03) higher risk of vomiting; a significant delay in MTX elimination implied a 5.76-fold higher risk of mucositis (p < 0.001). An increase of 1 micro mol/L in the MTX concentration 24 hours after the end of the infusion (Cp(24h)) led to a 43% increase in the risk of renal toxicity (p < 0.001). Hematologic toxicity was significantly conditioned by the baseline leukocyte count and Cp(24h) (p < 0.001). CONCLUSIONS: The analysis of high-dose MTX pharmacokinetic/pharmacodynamic relationship to toxicity has led to equations able to predict toxicity that are easily applicable to daily practice. Cp(24h) >3.5 micro mol/L was confirmed as an indicator of high risk of toxicity.

Adolescent↗