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PubMed2005

Cesarean delivery in Native American women: are low rates explained by practices common to the Indian health service?

BACKGROUND: Studying populations with low cesarean delivery rates can identify strategies for reducing unnecessary cesareans in other patient populations. Native American women have among the lowest cesarean delivery rates of all United States populations, yet few studies have focused on Native Americans. The study purpose was to determine the rate and risk factors for cesarean delivery in a Native American population. METHODS: We used a case-control design nested within a cohort of Native American live births, > or = 35 weeks of gestation (n = 789), occurring at an Indian Health Service hospital during 1996-1999. Data were abstracted from the labor and delivery logbook, the hospital's primary source of birth certificate data. Univariate and multivariate analyses examined demographic, prenatal, obstetric, intrapartum, and fetal factors associated with cesarean versus vaginal delivery. RESULTS: The total cesarean rate was 9.6 percent (95% CI 7.2-12.0). Nulliparity, a medical diagnosis, malpresentation, induction, labor length > 12.1 hours, arrested labor, fetal distress, meconium, and gestations < 37 weeks were each significantly associated with cesarean delivery in unadjusted analyses. The final multivariate model included a significant interaction between induction and arrested labor (p < 0.001); the effect of arrested labor was far greater among induced (OR 161.9) than noninduced (OR 6.0) labors. Other factors significantly associated with cesarean delivery in the final logistic model were an obstetrician labor attendant (OR 2.4; p = 0.02) and presence of meconium (OR 2.3; p = 0.03). CONCLUSIONS: Despite a higher prevalence of medical risk factors for cesarean delivery, the rate at this hospital was well below New Mexico (16.4%, all races) and national (21.2%, all races) cesarean rates for 1998. Medical and practice-related factors were the only observed independent correlates of cesarean delivery. Implementation of institutional and practitioner policies common to the Indian Health Service may reduce cesarean deliveries in other populations.

Adolescent↗

PubMed1999

Prognostic factors for the outcome of chemotherapy in advanced soft tissue sarcoma: an analysis of 2,185 patients treated with anthracycline-containing first-line regimens--a European Organization for Research and Treatment of Cancer Soft Tissue and Bone Sarcoma Group Study.

PURPOSE: A total of 2,185 patients with advanced soft tissue sarcomas who had been treated in seven clinical trials investigating the use of doxorubicin- or epirubicin-containing regimens as first-line chemotherapy were studied in this prognostic-factor analysis. PATIENTS AND METHODS: Overall survival time (median, 51 weeks) and response to chemotherapy (26% complete response or partial response) were the two end points. The cofactors were sex; age; performance status; prior therapies; the presence of locoregional or recurrent disease; lung, liver, and bone metastases at the time of entry onto the trial; long time period between the initial diagnosis of sarcoma and entry onto the study; and histologic type and grade. RESULTS: Univariate analyses showed (a) a significant, favorable influence of good performance status, young age, and absence of liver metastases on both survival time and response rate, (b) a significant, favorable influence of low histopathologic disease grade on survival time, despite a significantly lower response rate, (c) increased survival time for patients with a long time period between the initial diagnosis of sarcoma and entry onto the study, despite equivalent response rates, and (d) increased survival time with liposarcoma or synovial sarcoma, a decreased survival time with malignant fibrous histiocytoma, a lower response rate with leiomyosarcoma, and a higher response rate with liposarcoma (P < .05 for all log-rank and chi2 tests). The Cox model selected good performance status (P < .0001), absence of liver metastases (P = .0001), low histopathologic grade (P = .0002), long time lapse since initial diagnosis (P = .0004), and young age (P = .0045) as favorable prognostic factors of survival time. The logistic model selected absence of liver metastases (P < .0001), young age (P = .0024), high histopathologic grade (P = .0051), and liposarcoma (P = .0065) as favorable prognostic factors of response rate. CONCLUSION: This analysis demonstrates that for advanced soft tissue sarcoma, response to chemotherapy is not predicted by the same factors as is overall survival time. This needs to be taken into account in the interpretation of trials assessing the value of new agents for this disease on the basis of response to treatment.

Adult↗

PubMed2006

Classification scheme for phenomenological universalities in growth problems in physics and other sciences.

A classification in universality classes of broad categories of phenomenologies, belonging to physics and other disciplines, may be very useful for a cross fertilization among them and for the purpose of pattern recognition and interpretation of experimental data. We present here a simple scheme for the classification of nonlinear growth problems. The success of the scheme in predicting and characterizing the well known Gompertz, West, and logistic models, suggests to us the study of a hitherto unexplored class of nonlinear growth problems.

Algorithms↗

PubMedDate not supplied

Logistic representation of the sensitometric response of screen-film systems: empirical validation.

An empirical logistic model that linearizes the sensitometric response data of screen-film systems over the entire dynamic range of exposures is presented. This linearization is evident when the net optical densities are scaled as fractions of the net saturation density and plotted on commercial logit, probit, or double-log paper, except under conditions of reciprocity law failure. Weighted linear regression analysis shows that the intercept, but not the slope, depends on the screen-film system used. Previous work indicates that the slope is also independent of development time and photon energy. The model is verified through an analysis of tabulated sensitometric data published by the Center for Devices and Radiological Health.

Logistic Models↗

PubMed1998

Somatosensory discrimination of shape: prediction of success in normal volunteers and parkinsonian patients.

Tactile discrimination of macrogeometric objects in a two-alternative forced-choice procedure represents a complex task including somatosensory and higher-order cognitive processing. The objects for somatosensory discrimination were rectangular parallelepipeds that differed in oblongness only. They were presented in sequential pairs to 12 normal volunteers and 13 parkinsonian patients. Owing to the dichotomy of the task, we calculated estimates of the probability of a correct answer by a binomial approach. The probability of a correct answer could be calculated on the basis of a logistic model ensuring that the probability values lie in the interval [0, 1]. The relationship between the probability of a correct answer and the difference in oblongness of the objects could be described solely by one coefficient determined by logistic regression. This coefficient summarized the effectiveness of the simultaneous and consecutive operations inherent in the task and allowed characterization of performances in groups and individuals.

Adult↗

PubMed1993

Regression analysis of grouped survival data: informative censoring and double sampling.

To analyze grouped survival data subject to informative censoring, we propose the following two-part model: a logistic regression model for the hazard for failure, given covariates and a logistic regression model for the hazard for informative censoring, given time of failure and covariates. We fit the model to survival data arising from a double sampling design: In a full follow-up (FF) sample subjects are followed after censoring, and in a partial follow-up (PF) sample subjects are not followed after censoring. We illustrate the methodology using data from a study of wound infection in which patients in the PF sample are censored by release from the hospital, whereas patients in the FF sample are followed after hospital release. We discuss identifiability when there is only a PF sample. We also consider how the allocation between the PF and FF samples affects the precision of estimates.

Follow-Up Studies↗

PubMed1991

A study of the shape of dose-response curves for acute lethality at low response: a "megadaphnia study".

Dose-response curves were developed for the immobilization response in Daphnia magna to four toxicants. The purpose of this work was to study the effect of the form of the model and the number of concentration levels used on the estimates of typical low-dose effective concentrations (1%, 5%, 10%). The generalized four-parameter logistic model was used as the reference. When using 12 concentration levels, one of the logistic family two- or three-parameter models was shown reliably to represent each of these various sets of dose-response data, and to provide adequate estimates of EC01 and EC05, as well as EC10 and EC50. For two of the toxicants, an asymmetric model was required. When reducing the number of concentrations to five, the EC10 and EC50 were well estimated by the probit model, with acceptable results at the EC05 level.

Animals↗

PubMed2004

National examination of compliance predictors and the immunization status of children: precursor to a developmental model for health systems.

OBJECTIVES: The gap between children's immunization requirements and actual compliance is staggering. Using a national survey instrument, the purpose of this study was to analyze the relationship between select predictors and immunization status in children between 19 months and 6 years of age. METHODS: From the 1998 Medical Expenditure Panel Survey, 1575 children were included in a multivariate logistical model. Outcomes were measured as compliance with approved vaccination regimens. RESULTS: Only 67% of children between 19 months and 6 years old were compliant with all recommended vaccines. However, nonminority children with health insurance from families with income above the federal poverty line or living outside a metropolitan statistical area were more likely to be vaccinated. Children of older or educated parents likewise tended to have complete immunization. CONCLUSIONS: Analyzing childhood immunization via parental characteristics identifies prevalent predictors of compliance. Outcomes suggest potential strategies for health systems to focus on children's health issues--specifically immunizations.

Child, Preschool↗

PubMed1995

Intracoronary thrombus: still a risk factor for PTCA failure?

Pre-existing intracoronary thrombus has been associated with an increased risk of percutaneous transluminal coronary angioplasty (PTCA) failure. Whether intracoronary thrombus is an independent risk factor for failure is uncertain, as conflicting data exist in the literature. Additionally, given advances in patient selection and angioplasty balloon design, it is uncertain whether the current risk posed by intracoronary thrombus is as substantial as that in the early angioplasty experience. The primary objective of this study was to first assess whether pre-existing coronary thrombus was an independent predictor of angioplasty failure and if so, whether the risk due to thrombus had changed from the early angioplasty experience to the present time. Our prospectively collected angioplasty data base was used to identify individuals undergoing single-vessel angioplasty of a thrombus-containing segment from January 1, 1984 through December 1, 1991. Univariate and multivariate stepwise logistic regression techniques were utilized to analyze clinical, angiographic, and procedural characteristics associated with angioplasty failure. The study period was divided into three separate time periods and these used as variables in our multivariate analysis. In the study population that consisted of 2,699 patients with single-vessel angioplasty, univariate analysis demonstrated that among many factors, thrombus was importantly associated with angioplasty failure (P < 0.0001). A multivariate logistic model of angioplasty failure was developed and thrombus achieved independent predictive significance in this model.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1996

Physician implementation of and patient adherence to recommendations from comprehensive geriatric assessment.

PURPOSE: The goals of this study were to develop and determine the feasibility of interventions designed to increase both primary care physician implementation of and patient adherence to recommendations from ambulatory-based consultative comprehensive geriatric assessment (CGA), and to identify sociodemographic and intervention-related predictors of physician and patient adherence. PATIENTS AND METHODS: One hundred thirty-nine community-dwelling older persons who failed a screen for functional impairment, depressive symptoms, falls, or urinary incontinence received outpatient CGA consultation. These patients and the 115 physicians who provided primary care for them received one of three adherence interventions, each of which had a physician education component and a patient education and empowerment component. Recommendations were classified as physician-initiated or self-care and as "major" or "minor"; one was deemed "most important". Adherence rates were determined on the basis of face-to-face interviews with patients. RESULTS: Based on 528 recommendations for 139 subjects, physician implementation of "most important" recommendations was 83% and of major recommendations was 78.5%. Patient adherence with physician-initiated "most important" and "major" recommendations were 81.8% and 78.8% respectively. In multivariate models, only the status of the recommendation of "most important" (odds ratio 2.4, 95% CI [confidence interval] 1.3 to 4.5) and health maintenance organization (HMO) status of the patient (odds ratio 2.1, 95% CI 1.3 to 3.6) remained significant in predicting physician implementation. The logistic model predicting patient adherence to physician-initiated recommendations included male patient gender (odds ratio 3.1, 95% CI 1.3 to 7.0), the status of the recommendation of "most important" (odds ratio 1.9, 95% CI 1.0 to 3.8), total number of recommendations (odds ratio 0.7, 95% CI 0.5 to 0.9), and total number of problems identified by CGA (odds ratio 1.8, 95% CI 1.2 to 2.7). CONCLUSIONS: These findings indicate that relatively modest interventions strategies are feasible and lead to high levels of physician implementation of and patient adherence to physician-initiated CGA recommendations. These interventions appear to be particularly effective in HMO patients and for recommendations that were deemed to be "most important".

Accidental Falls↗

PubMed1999

Solitary pulmonary nodules: clinical prediction model versus physicians.

OBJECTIVE: To determine whether a clinical prediction model developed to identify malignant lung nodules based on clinical data and radiologic lung nodule characteristics could predict a malignant lung nodule diagnosis with higher accuracy than physicians. MATERIAL AND METHODS: One hundred cases were obtained by using a stratified random sample from a retrospective cohort of 629 patients with newly discovered 4- to 30-mm radiologically indeterminate solitary pulmonary nodules (SPNs) on chest radiography. A chest radiologist, pulmonologist, thoracic surgeon, and general internist made predictions of a malignant lesion and recommendations for management (thoracotomy, transthoracic needle aspiration biopsy, or observation) on the basis of radiologic and clinical data used to develop the clinical prediction rule. The predictions of a malignant lung nodule were compared with the probability of malignant involvement from a previously validated clinical prediction model to identify malignant nodules on the basis of three clinical characteristics (age, smoking status, and history of cancer greater than or equal to 5 years previously) and three radiologic characteristics (nodule diameter, spiculation, and upper lobe location). RESULTS: Receiver operating characteristic analysis showed no significant difference between the logistic model and the physicians' predictions. Calibration curves revealed that physicians overestimated the probability of a malignant lesion in patients with low risk of malignant disease by the prediction rule; this finding suggests a potential for the decision rule to improve the management of patients with SPNs that are likely to be benign. CONCLUSION: The prediction model was not better than physicians' predictions of malignant SPNs. The prediction rule may have potential to improve the management of patients with SPNs that are likely to be benign.

Diagnosis, Differential↗

PubMed2006

Desired family size, family planning and fertility in Ethiopia.

This paper models the proximate determinants of children born to over 13,000 Ethiopian women and of the women's stated preferences for additional births using the data from the Ethiopian Demographic and Health Survey 2000. Empirical models for the number of children born to women were estimated using Poisson and ordinal regressions. The results show the importance of variables such as maternal education for smaller family size, and that variables reflecting desired family size are strong predictors of the numbers of children born to women. Secondly, binary logistic models for dichotomous variables for women not wanting more children and if getting pregnant would be a 'big problem' showed non-linear effects of the surviving and 'ideal' number of children. Moreover, the results indicated a desire on the part of women to limit family size, especially as the number of surviving children increased. Probit models were estimated to address potential endogeneity of certain variables. Overall, the results indicated that counselling couples about small family size and increasing the utilization of health care services can lower fertility in Ethiopia.

Educational Status↗

PubMed2000

Microchimerism and rejection: a meta-analysis.

AIMS: To study the relationship between graft rejection and microchimerism with and without donor bone marrow infusion in recipients of kidney, liver, heart and lung transplants. Selection of manuscripts. Thirty-seven manuscripts presenting clinical data on microchimerism and rejection, published between 1991 and 1997, were identified. Of these, 16 were excluded due to duplication or insufficient data. Inclusion criteria were data on microchimerism, bone marrow infusion and rejection episodes. STATISTICAL TESTS: A mixed effect logistic model was used to test for homogeneity of transplant centers. The centers were found to be homogeneous for rejection rates controlling for microchimerism and bone marrow infusion. Using rejection episodes at 3, 6, and 12 months post-transplant as the outcome, we evaluated logistic regression models to derive odds ratios for rejection with microchimerism and with bone marrow infusion for each organ. RESULTS: Microchimerism was generally associated with a higher incidence of acute rejection for heart, lung, and kidney transplants and a lower incidence for liver transplants, especially at 12 months and above. Bone marrow infusion decreased the risk of acute rejection for heart transplants and increased the risk for lung and, to a lesser extent, for liver transplants. No consistent effect was seen in kidney transplants. At 12 months and longer, microchimerism was associated with a decreased incidence of chronic rejection in recipients of lung transplants, but there were insufficient data to determine this outcome for other organs. CONCLUSIONS: (i) Microchimerism was detected in the majority of patients. (ii) The effect of microchimerism and bone marrow infusion on rejection episodes varied with the organ and, for a given organ, it was time-dependent. (iii) These findings demonstrate the need for more extensive studies on microchimerism and donor-specific hyporesponsiveness.

Graft Rejection↗

PubMed2000

A model for pretest probability of lymph node metastasis from cutaneous Melanoma.

Although many statistical models have been developed to predict survival in cutaneous melanoma, few predict the end point of regional lymph node metastasis shortly after the diagnosis of melanoma. We used routine clinical and histologic data from 573 patients referred to the Duke University Melanoma Clinic, Durham, NC, during the 1980s and 1990s who underwent lymph node resections during the first year after the diagnosis of primary cutaneous melanoma. The outcome we modeled (using the logistic regression model) was the probability of lymph node metastasis. We found that tumor thickness was the variable most significantly associated with the probability of nodal metastasis, and the presence of ulceration and tumor location also were significant, but age, sex, and mitotic rate were not. When the resulting logistic model predicted that the probability of nodal metastasis was more than .6, 93 of 115 patients had nodal metastasis. When the model predicted that the probability was less than .3, just 32 of 88 patients had positive nodes. Furthermore, after the result of the node sampling was known, Cox model analysis demonstrated that the pretest probability added significant information about subsequent survival.

Biopsy↗

PubMed1990

Optimality assessment in the enzyme-linked immunosorbent assay (ELISA).

An optimality criterion is proposed for evaluating the precision of alternative designs in the enzyme-linked immunosorbent assay. Assay profiles are represented as four-parameter logistic functions with parameter estimation based on either a weighted nonlinear regression or a simple nonlinear regression after a logarithmic transformation. Assay design changes are characterized in terms of their effects on parameters in the four-parameter logistic model. General optimality results are derived for the variance of relative potency estimates in routine assay applications.

Biometry↗

PubMed1999

Comparison of population-based models of risk factors for TIA and ischemic stroke.

OBJECTIVE: To determine whether there is a difference in the risk factors for ischemic stroke and for TIA. BACKGROUND: TIA is associated with a high risk for ischemic stroke, but some have considered TIA as mild ischemic stroke. Prevention of disabling stroke is sufficient reason to label TIA as a precursor for stroke, but some risk factors may be more or less associated with TIA than with ischemic stroke, suggesting differences in mechanism. METHODS: The medical records linkage system for the Rochester Epidemiology Project provided the means of identifying first episodes of TIA in the Rochester, MN population among those who had not had ischemic stroke. Control subjects were selected from an enumeration of the population through the medical records. The exposure to various risk factors was ascertained. The conditional likelihood approach to estimate the parameters of a multiple logistic model permitted estimation of the OR for TIA for each risk factor while adjusting for confounding variables. RESULTS: The multivariable logistic regression model for TIA shows that the estimates of the ORs for ischemic heart disease, hypertension, persistent atrial fibrillation, diabetes mellitus, and cigarette smoking are similar to the ORs for those variables in the ischemic stroke model. However, the OR for mitral valve disease in the TIA model is 0.4, suggesting that mitral valve disease is unlikely to be associated with cerebral ischemic episodes that are brief enough to be called TIA.

Brain Ischemia↗

PubMed2001

Bayesian semiparametric analysis of developmental toxicology data.

Modeling of developmental toxicity studies often requires simple parametric analyses of the dose-response relationship between exposure and probability of a birth defect but poses challenges because of nonstandard distributions of birth defects for a fixed level of exposure. This article is motivated by two such experiments in which the distribution of the outcome variable is challenging to both the standard logistic model with binomial response and its parametric multistage elaborations. We approach our analysis using a Bayesian semiparametric model that we tailored specifically to developmental toxicology studies. It combines parametric dose-response relationships with a flexible nonparametric specification of the distribution of the response, obtained via a product of Dirichlet process mixtures approach (PDPM). Our formulation achieves three goals: (1) the distribution of the response is modeled in a general way, (2) the degree to which the distribution of the response adapts nonparametrically to the observations is driven by the data, and (3) the marginal posterior distribution of the parameters of interest is available in closed form. The logistic regression model, as well as many of its extensions such as the beta-binomial model and finite mixture models, are special cases. In the context of the two motivating examples and a simulated example, we provide model comparisons, illustrate overdispersion diagnostics that can assist model specification, show how to derive posterior distributions of the effective dose parameters and predictive distributions of response, and discuss the sensitivity of the results to the choice of the prior distribution.

2,4,5-Trichlorophenoxyacetic Acid↗

PubMed2003

Modelling autoimmune rheumatic disease: a likelihood rationale.

Immunoglobulins (Igs) and autoantibodies are commonly tested in sera from patients with suspected rheumatic disease. To evaluate the clinical utility of the tests in combination, we investigated sera from 351 patients with autoimmune rheumatic disease (ARD) rheumatoid arthritis (RA), systemic lupus erythematosus (SLE) and Sjögren's syndrome (SS) and 96 patients with nonautoimmune rheumatic disease (NAD) (fibromyalgia, osteoarthritis, etc.). Antinuclear antibodies (ANA), rheumatoid factor (RF), antibodies against DNA and extractable nuclear antigens (anti-ENA), IgG, IgA and IgM were measured for all patients. Logistic regression analysis of test results was used to calculate each patient's probability for belonging to the ARD or NAD group as well as likelihood ratios for disease. Test accuracy was investigated using receiver-operating characteristic (ROC) plots and nonparametric ROC analysis. Neither concentrations of IgG, IgA, IgM, anti-DNA nor anti-ENA gave a significant effect on diagnostic outcome. Probabilities for disease and likelihood ratios calculated by combining RF and ANA performed significantly better at predicting ARD than utilization of the diagnostic tests in isolation (P < 0.001). At a cut-off level of P = 0.73 and likelihood ratio = 1, the logistic model gave a specificity of 93% and a sensitivity of 75% for the differentiation between ARD and NAD. When compared at the same level of specificity, ANA gave a sensitivity of 37% and RF gave a sensitivity of 56.6%. Dichotomizing ANA and RF as positive or negative did not reduce the performance characteristics of the model. Combining results obtained from serological analysis of ANA and RF according to this model will increase the diagnostic utility of the tests in rheumatological practice.

Adolescent↗