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PubMed2003

[Advances of study on the formulae based on a correlation and linear regression between the potassium concentration in the vitreous humor and the post-mortem interval and the factors which modifies the relationship].

In this paper we reviewed the formulae and analyzed the factors which modified the relationship and estimate the time of death as precise as possible by potassium concentration in vitreous humor. The extra factors including numbers of the cases, cause of death, different eye of both, the urea or/and creatinine in vitreous humor, environmental temperature, sampling techniques, experimental and analytical method were also mentioned.

Aqueous Humor↗
PubMed2003

Inference for a linear regression model with an interval-censored covariate.

Interval-censored observations of a response variable are a common occurrence in medical studies, and usually result when the response is the elapsed time until some event whose occurrence is periodically monitored. In this paper we consider a multivariate regression setting in which the explanatory variable is interval censored. Use of an ad hoc method of analysis for such data, such as taking the midpoint of the interval-censored covariate and applying ordinary least-squares, is not in general valid. We develop a likelihood approach, together with a two-step conditional algorithm, to jointly estimate the regression coefficients as well as the marginal distribution of the covariate. The resulting estimators are asymptotically normal. The performance of the method is assessed via simulations, and illustrated using data from a recent HIV/AIDS clinical trial to assess the association between waiting time between indinavir failure and subsequent viral load at enrolment. Extensions of the procedure to other parametric distributions are discussed.

Adult↗
PubMed1993

Linear regressive analysis using prostate-specific antigen doubling time for predicting tumor biology and clinical outcome in prostate cancer.

BACKGROUND: This study was undertaken to calculate the prostate-specific antigen doubling time (PSA-DT) of prostate cancers recurrent after external beam radiation therapy and to investigate if a correlation exists between the PSA-DT and the clinical behavior of prostate cancer as a possible reflection of the tumor doubling time. METHODS: Twenty-two patients treated with external beam radiation between October 1985 and October 1990 for clinical stages B1, B2, and C (T2a, T2b, T3) prostate cancer experienced PSA elevation as their only sign of failure. Serial PSA determinations are available before initiation of any secondary treatment and these have been used to calculate PSA-DT. RESULTS: The results of this study reveal that the PSA-DT is a constant (r > or = 0.98). Mathematically, this means the PSA value is growing exponentially and may represent tumor growth in the exponential phase. Second, the PSA-DT was found to be linearly correlated (r = 0.86) with the interval to clinical relapse after PSA failure. Graphically, the slope of this correlation is equal to the number of PSA-DT (4.5 with 95% confidence interval [3.6]) required before clinical disease manifests after PSA failure. Using this relationship, one can delineate those patients with aggressive tumor biology (PSA-DT < 3.8 months) who require immediate therapeutic intervention versus a relatively indolent tumor biology (PSA-DT > or = 3.8 months) who can be spared the morbidity and expense of androgen deprivation therapy until clinical recurrence manifests. Furthermore, in the pretreatment setting, observation rather than treatment may be indicated for patients with PSA-DT for 18 months or more, because the disease may not become clinically apparent during the patient's lifetime. CONCLUSION: PSA-DT after radiation therapy may reflect the tumor doubling time and has implications in the posttherapy setting regarding the optimal time of intervention with androgen deprivation and in the pretreatment setting regarding the necessity for treatment rather than observation.

Cell Division↗
PubMed2006

QSAR analysis of tyrosine kinase inhibitor using modified ant colony optimization and multiple linear regression.

Quantitative structure-activity relationship (QSAR) models of inhibiting action of some analogues of 4-(3-bromoanilino)-6,7-dimethoxyquinazoline on epidermal growth factor receptor tyrosine kinase were constructed using modified ant colony optimization (ACO) method. As a comparison to this method, the evolutionary algorithm (EA) was also tested. It has been demonstrated that the modified ACO is a useful tool for variable selection comparable to EA. In the selected descriptors, electronic descriptor sigma(Y)(-) is the most important descriptor in predicting EGFR inhibitory activity. Electron-donating groups such as Y-substituents enhance the activity as evident by negative sigma(Y)(-). In addition, for quinazoline substituents, nitro group has a large deactivating effect.

Algorithms↗
PubMed1998

The conundrum of the Glasgow Coma Scale in intubated patients: a linear regression prediction of the Glasgow verbal score from the Glasgow eye and motor scores.

BACKGROUND: The Glasgow Coma Scale (GCS), which is the foundation of the Trauma Score, Trauma and Injury Severity Score, and the Acute Physiology and Chronic Health Evaluation scoring systems, requires a verbal response. In some series, up to 50% of injured patients must be excluded from analysis because of lack of a verbal component for the GCS. The present study extends previous work evaluating derivation of the verbal score from the eye and motor components of the GCS. METHODS: Data were obtained from a state trauma registry for 24,565 unintubated patients. The eye and motor scores were used in a previously published regression model to predict the verbal score: Derived Verbal Score = -0.3756 + Motor Score * (0.5713) + Eye Score * (0.4233). The correlation of the actual and derived verbal and GCS scales were assessed. In addition the ability of the actual and derived GCS to predict patient survival in a logistic regression model were analyzed using the PC SAS system for statistical analysis. The predictive power of the actual and the predicted GCS were compared using the area under the receiver operator characteristic curve and Hosmer-Lemeshow goodness-of-fit testing. RESULTS: A total of 24,085 patients were available for analysis. The mean actual verbal score was 4.4 +/- 1.3 versus a predicted verbal score of 4.3 +/- 1.2 (r = 0.90, p = 0.0001). The actual GCS was 13.6 + 3.5 versus a predicted GCS of 13.7 +/- 3.4 (r = 0.97, p = 0.0001). The results of the comparison of the prediction of survival in patients based on the actual GCS and the derived GCS show that the mean actual GCS was 13.5 + 3.5 versus 13.7 + 3.4 in the regression predicted model. The area under the receiver operator characteristic curve for predicting survival of the two values was similar at 0.868 for the actual GCS compared with 0.850 for the predicted GCS. CONCLUSIONS: The previously derived method of calculating the verbal score from the eye and motor scores is an excellent predictor of the actual verbal score. Furthermore, the derived GCS performed better than the actual GCS by several measures. The present study confirms previous work that a very accurate GCS can be derived in the absence of the verbal component.

Glasgow Coma Scale↗
PubMed2004

QSAR analysis of cyclooxygenase inhibitor using particle swarm optimization and multiple linear regression.

Quantitative structure-activity relationship (QSAR) models of inhibiting action of some diarylimidazole derivatives on cylcooxygenase (COX) enzyme were constructed using modified particle swarm optimization (PSO) method. As a comparison to this method, the genetic algorithm (GA) was also tested. It has been demonstrated that the modified PSO is a useful tool for variable selection comparable to GA and even superior to GA. QSAR models are constructed separately for COX-2 inhibitory activity and selectivity of COX-2 inhibition over COX-1. The spatial descriptors play a key role in the compounds' activity and selectivity to COX-2, especially Jurs descriptors. Polar interactions are the principal binding strength between compounds and COX-2 enzyme. In addition, the aqueous desolvation free energy (FH2O) value of substituent will affect the COX-2 inhibitory activity, while the charge distribution can affect the selectivity to COX-2.

Cyclooxygenase Inhibitors↗
PubMed1998

Extending the simple linear regression model to account for correlated responses: an introduction to generalized estimating equations and multi-level mixed modelling.

Much of the research in epidemiology and clinical science is based upon longitudinal designs which involve repeated measurements of a variable of interest in each of a series of individuals. Such designs can be very powerful, both statistically and scientifically, because they enable one to study changes within individual subjects over time or under varied conditions. However, this power arises because the repeated measurements tend to be correlated with one another, and this must be taken into proper account at the time of analysis or misleading conclusions may result. Recent advances in statistical theory and in software development mean that studies based upon such designs can now be analysed more easily, in a valid yet flexible manner, using a variety of approaches which include the use of generalized estimating equations, and mixed models which incorporate random effects. This paper provides a particularly simple illustration of the use of these two approaches, taking as a practical example the analysis of a study which examined the response of portable peak expiratory flow meters to changes in true peak expiratory flow in 12 children with asthma. The paper takes the reader through the relevant practicalities of model fitting, interpretation and criticism and demonstrates that, in a simple case such as this, analyses based upon these model-based approaches produce reassuringly similar inferences to standard analyses based upon more conventional methods.

Adolescent↗
PubMed2000

Patient-specific analysis of sequential haematological data by multiple linear regression and mixture distribution modelling.

Automated storage and analysis of the results of serial haematologic studies are now technically feasible with present-day laboratory instruments and devices for data storage and processing. In current practice, physicians mentally compare a laboratory result with previous values and use their clinical judgement to determine the significance of any change. To provide a statistical basis for this process, we describe a new approach for the detection of changes in patient-specific sequential measurements of standard haematologic laboratory tests. These methods include hierarchical multiple regression modelling, with a weighted minimum risk criteria for model selection, to choose models indicating changes in mean values over time. This study is the first to analyse sequential patient-specific distributions of laboratory measurements, utilizing mixture distribution modelling with systematic selection of starting values for the EM algorithm. To evaluate these statistical methods under controlled conditions, we studied 11 healthy human volunteers who were depleted of iron by serial phlebotomy to iron-deficiency anaemia, then treated with oral iron supplements to replete iron stores and correct the anaemia. Application of sequential patient-specific analyses of haemoglobin, haematocrit, and mean cell volume showed that significant departures from past values could be identified, in many cases, even when values were still within the population reference ranges. Additionally, for all subjects sequential alterations in red blood cell volume distributions during development of iron-deficiency anaemia could be characterized and quantified. These methods promise to provide more sensitive techniques for improved diagnostic evaluation of developing anaemia and serial monitoring of response to therapy.

Administration, Oral↗
PubMed1992

Identifying coronary artery disease in women by heart rate adjustment of ST-segment depression and improved performance of linear regression over simple averaging method with comparison to standard criteria.

Performance of exercise electrocardiography for the detection of coronary artery disease (CAD) in women has been limited by relatively poor sensitivity and specificity of standard test criteria. Recent studies suggest that diagnostic methods incorporating heart rate (HR) adjustment of ST-segment depression during exercise may improve the accuracy of exercise testing in women, but the relative performance of different rate-adjusted methods for this purpose is unknown. To assess the effect of gender on relative test performance of the ST-segment/HR (ST/HR) slope, the simple ST/HR index, the HR-recovery loop, and standard ST-depression criteria for the identification of CAD, the exercise electrocardiograms of 254 patients with known or suspected CAD (67 women and 187 men) and of 150 clinically normal subjects (29 women and 121 men) were analyzed. Specificity of each method was comparable in men and women: ST/HR slope 98% (118 of 121) vs 97% (28 of 29), ST/HR index 97% (117 of 121) vs 97% (28 of 29), and HR-recovery loop 96% (116 of 121) vs 93% (27 of 29). In contrast, although there was no difference in sensitivity of the ST/HR slope (95% [177 of 187] vs 93% [62 of 67]; p = not significant [NS]) or HR-recovery loop (90% [168 of 187] vs 87% [58 of 67]; p = NS) between men and women, the ST/HR index was less sensitive for CAD in women than in men (82% [55 of 67] vs 93% [173 of 187]; p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2003

Correlation and linear regression between blood pressure decreases after a test dose injection of propofol and that following anaesthesia induction.

Propofol reduces systemic vascular resistance and suppresses cardiac function when injected rapidly. In this study we investigated whether blood pressure decrease after a minimal dose (test-dose) injection of propofol correlates with that after an induction-dose injection. Patients were randomly divided into two groups; anaesthesia was induced in group A (n = 60) using 1.5 mg/kg propofol and in group B (n = 61) using 2.0 mg/kg. Blood pressure reduction after a minimal dose injection (0.4 mg/kg) was examined non-invasively prior to anaesthetic induction. Bispectral Index monitoring was measured and sedation level scored to evaluate anaesthetic depth. After the minimal dose injection, 18 of 121 patients showed behaviour suggesting minor disinhibition, five patients were sedated and seven were drowsy. Oxygen saturation was not significantly changed after test-dose injection. Reduction in systolic blood pressure (mean +/- SD) was 17 +/- 11 mmHg after the minimal dose injection, 42 +/- 20 mmHg after a 1.5 mg/kg induction dose injection, and 42 +/- 22 mmHg after a 2.0 mg/kg induction-dose injection. In both groups, blood pressure after induction was significantly lower than the control value (P < 0.05). In both groups, a positive correlation was observed between blood pressure reduction after the minimal dose injection and that after the induction-dose injection [P < 0.01, R value for systolic blood pressure correlation in group A 0.712 (P < 0.01) and in group B 0.758 (P < 0.01)]. We concluded there was a positive correlation between blood pressure reduction after a minimal (test-dose) injection and that after an induction-dose injection.

Adult↗
PubMed1998

Measurement of overinflation by multiple linear regression analysis in patients with acute lung injury.

Strategies to optimize alveolar recruitment and prevent lung overinflation are central to ventilatory management of patients with acute lung injury (ALI). The recent description of overinflation using multilinear regression analysis of airway pressure (Paw) and flow (V') data allows a functional assessment of lung mechanics. However, this technique has not been studied in ALI patients. During 15 positive end-expiratory pressure (PEEP) trials in 10 ALI patients, respiratory elastance was partitioned into volume-independent (E1) and volume-dependent (E2VT) components, where Paw=(E1+E2VT)V+RrsV'+Po; where V is volume, VT is tidal volume, Rrs is respiratory resistance and Po is static recoil pressure at end-expiration (equivalent to total PEEP). Then, %E2 was calculated as (100E2VT)/(E1+E2VT); a measure of lung overinflation when %E2>30%. Alveolar recruitment, assessed as a PEEP-induced increase in V>50 mL at a constant Paw occurred in 14 of 15 trials (299+/-34 mL, mean+/-SEM), but was independent of the degree of lung inflation. Lung overinflation was common (six of 15 clinically set PEEP levels) and occurred despite a dynamic elastic distending pressure (Pel,dyn) <30 cmH2O during 18 of 36 PEEP titrations. During a PEEP titration the resultant %E2 was directly related to delta(peak airway pressure-Po) (rs=0.86, p<0.001) and delta(Pel,dyn-Po) (rs=0.89, p<0.001). The 95% predictive intervals for a 2 cmH2O change in either driving pressure were %E2 values of 30.4-68.1% and 32.8-69.2%, respectively. Single or continuous measurement of %E2 (a measure of lung inflation) is a readily available method for titrating ventilatory parameters. Further, during a positive end-expiratory pressure titration a change in ventilatory driving pressure > or =2 cmH2O is indicative of overinflation.

Acute Disease↗
PubMed2005

A Bayesian hierarchical non-linear regression model in receiver operating characteristic analysis of clustered continuous diagnostic data.

Receiver operating characteristic (ROC) analysis is a useful evaluative method of diagnostic accuracy. A Bayesian hierarchical nonlinear regression model for ROC analysis was developed. A validation analysis of diagnostic accuracy was conducted using prospective multi-center clinical trial prostate cancer biopsy data collected from three participating centers. The gold standard was based on radical prostatectomy to determine local and advanced disease. To evaluate the diagnostic performance of PSA level at fixed levels of Gleason score, a normality transformation was applied to the outcome data. A hierarchical regression analysis incorporating the effects of cluster (clinical center) and cancer risk (low, intermediate, and high) was performed, and the area under the ROC curve (AUC) was estimated.

Bayes Theorem↗
PubMed1979

Kinetic parameter estimation by numerical algorithms and multiple linear regression: application to pharmacokinetics.

Two numerical examples are presented to illustrate the application of the proposed method of parameter estimation in pharmacokinetics. Results for a system exemplifying first-order kinetics indicate that parameters estimated by the proposed procedure compare favorably with those estimated by a nonlinear regression method. In a simulated example characterized by Michaelis-Menten elimination kinetics, the accuracy of the estimated parameters was comparable to that expected, verifying the validity of the method. The importance of the numerical approximation algorithms was demonstrated also.

Kinetics↗
PubMed1998

Is visual field evaluation using multiple correlations and linear regressions useful? An evaluation of Delphi perimetry.

BACKGROUND: Delphi perimetry is a method of visual field examination which produces a statistical estimation of the visual field by testing only four critical points of the central visual field. This study was performed to evaluate this technique for the detection of glaucomatous field loss. METHOD: Patients with glaucoma and ocular hypertension underwent Delphi perimetry and Humphrey visual field analysis (HVFA) program 24-2. The visual field results of both examination were compared. RESULTS: Of 262 eyes from 199 patients, 120 eyes showed glaucomatous defects by HVFA and 142 were normal. Delphi perimetry showed abnormal visual fields in 107 eyes, 13 of which were false-positive results as Humphrey visual fields were normal. Delphi classified 155 fields as normal, of which 26 were false negatives as Humphrey visual fields showed glaucomatous defects. Therefore, the sensitivity of Delphi perimetry for the detection of glaucomatous visual field defect was 78% and the specificity was 91%. In the 26 false-negative eyes, the most common defect missed was an isolated paracentral scotoma or an early nasal step. Furthermore, 27 of the 94 glaucomatous eyes classified as abnormal by Delphi had defects estimated by Delphi perimetry that corresponded poorly to the field loss demonstrated by Humphrey visual field analysis. Therefore, qualitative sensitivity and specificity of Delphi perimetry for producing an accurate representation of the location, extent and defect depth of glaucomatous visual field loss would be 48.8% and 72% respectively. CONCLUSION: In this study Delphi perimetry failed to give an accurate statistical estimation of the visual field in an unacceptably high number of cases; therefore, it cannot be recommended for clinical use.

False Positive Reactions↗