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PubMed1990

Sudden infant death syndrome among Asians in California.

We analyzed California linked birth and infant death records for 1978 to 1985 to determine the ethnic-specific incidence of sudden infant death syndrome in five Asian-American subgroups, and to assess the association of sudden infant death syndrome with cultural assimilation. The overall incidence of sudden infant death syndrome for these groups was 1.1/1000 live births (194 cases). The ethnic-specific incidence was statistically associated with the immigration status of each ethnic group, as measured by the proportion of all live births for which the mother was born in the United States, with a higher incidence for groups that have been in the United States for the longest period. A logistic model was used to examine simultaneously the association of sudden infant death syndrome with maternal ethnicity, ethnic homogeneity or heterogeneity of the parents, and maternal birthplace (United States, or elsewhere). The logistic analysis did not yield statistically significant evidence to support cultural assimilation as a factor in the incidence of sudden infant death syndrome for these groups. This finding may be due to small sample size and inadequate indicators of assimilation. It may also be that other factors relating to immigration and selective migration affect the incidence of sudden infant death syndrome among Asian-Americans.

Adult↗

PubMed1984

Interpreting multiple logistic regression coefficients in prospective observational studies.

Multiple logistic models are frequently used in observational studies to assess the contribution of a risk factor to disease while controlling for one or more covariates. Often, the covariates are correlated with the risk factor, resulting in multiple logistic coefficients that are difficult to interpret. This paper highlights the problem of assessing the magnitude of a multiple logistic coefficient and proposes a supplemental procedure to the usual logistic analysis for describing the relationship between a risk factor and disease. An example is given, along with results that are not apparent when the multiple logistic coefficient is considered alone. Conclusions that are presented are important in biologic studies if describing the effect of a risk factor is influenced by correlation with a covariate.

Coronary Disease↗

PubMed1993

Blood lipids, the risk factor of cerebral infarction.

A hospital-based case-control study was undertaken at Prasat Neurological Hospital and Institute, Bangkok, in 1990 to determine the association between blood lipid variables (i.e., total cholesterol and triglycerides) and cerebral infarction. To alleviate the unwanted effects of sample selection a number of inclusion and exclusion criteria were also made. A total of 193 newly diagnosed cerebral infarction patients together with an equal number of age-sex-matched controls, male and female 45 to 84 years of age, were studied. The association was assessed by logistic regression analysis. Other potential risk factors for cerebral infarction were entered in the logistic models as covariates to be adjusted. The results showed that, total cholesterol and triglycerides were statistically significant related to cerebral infarction (p < 0.0001) in univariated analysis. After adjusting for the covariates through multivariate logistic regression analyses, total cholesterol remained significantly related to cerebral infarction (p = 0.0430) but triglycerides was not significant (p = 0.3953). Other factors, namely, hypertension, cardiac impairment, diabetes mellitus and hemoglobin concentration were strongly related to cerebral infarction in both the univariate and multivariate analyses. The interaction between blood lipids variables and potential risk factors was also assessed. The finding showed significant multiplicative interaction between triglyceride levels and diabetes mellitus status (p = 0.0026). Other interaction terms did not approach statistical significance.

Aged↗

PubMed1990

Prevalence of respiratory conditions among schoolchildren exposed to different levels of air pollutants in the Haifa Bay area, Israel.

During spring 1984, 2334 second and 2000 fifth-grade schoolchildren living in three Haifa Bay areas on the eastern Mediterranean coast with different levels of air pollution were studied. The parents of these children filled out American Thoracic Society and National Heart and Lung Institute health questionnaires, and the children performed the following pulmonary function tests (PFT); FVC, FEV1, FEV1/FEV, PEF, FEF50, and FEF75. A trend of higher prevalence of most reported respiratory symptoms was found for schoolchildren growing up in the medium and high pollution areas as compared with the low pollution area. Part of the reported respiratory diseases were significantly more common among children from the high pollution area. Models fitted for the respiratory conditions that differed significantly among the three areas of residence also included background variables that could be responsible for these differences. Relative risk values, which were calculated from the logistic models, were in the range of 1.38 for sputum with cold and 1.81 for sputum without cold for children from the high pollution area as compared with 1.00 for children from the low pollution area. All the measured values of PFT were within the normal range. There was no consistent trend of reduced pulmonary function that characterized any residential area.

Air Pollutants↗

PubMed1994

Fitting a two-parameter logistic item response model to clarify the psychometric properties of the Drug Use Screening Inventory for adolescent alcohol and drug abusers.

The suitability of fitting a two-parameter logistic item response model to the Drug Use Screening Inventory (DUSI) was assessed. In a sample of 846 adolescents, each of the 10 domains was found to be unidimensional. Invariance of the item parameters across different groups was also observed. The reliability coefficient, based on item response theory, was found to be superior. The results of these analyses indicate that the DUSI has sound psychometric properties.

Adolescent↗

PubMed1990

Application of the Cox model as a predictor of relative risk of coronary heart disease in the Albany Study.

Patients in long term studies of coronary heart disease may have different levels of risk during the course of study. Smoking habits, blood pressure, and obesity may change drastically during this period. The multiple logistic model, the most commonly used model for the analysis of coronary heart disease studies, does not consider survival time in assessment of the dependent covariates and does not account for the censoring which usually occurs in such studies. We propose a Cox model with time-dependent covariates to model the risk of coronary heart disease in the Albany study. The Cox model we fitted evaluates the patients' risk on the basis of the data at the last visit. With this methodology, we can evaluate whether it is advantageous for individuals to modify their risk of disease by their effecting changes in their covariates, that is to stop smoking, lose weight, change diet and so on. The important covariates that explain the risk of coronary heart disease were the same in our model as in the models used in the earlier reports. The estimated relative risks were slightly higher in most cases and lend more support to the need to encourage patients to achieve a better covariate state.

Adult↗

PubMed2005

Linkage mapping methods applied to the COGA data set: presentation Group 4 of Genetic Analysis Workshop 14.

Presentation Group 4 participants analyzed the Collaborative Study on the Genetics of Alcoholism data provided for Genetic Analysis Workshop 14. This group examined various aspects of linkage analysis and related issues. Seven papers included linkage analyses, while the eighth calculated identity-by-descent (IBD) probabilities. Six papers analyzed linkage to an alcoholism phenotype: ALDX1 (four papers), ALDX2 (one paper), or a combination both (one paper). Methods used included Bayesian variable selection coupled with Haseman-Elston regression, recursive partitioning to identify phenotype and covariate groupings that interact with evidence for linkage, nonparametric linkage regression modeling, affected sib-pair linkage analysis with discordant sib-pair controls, simulation-based homozygosity mapping in a single pedigree, and application of a propensity score to collapse covariates in a general conditional logistic model. Alcoholism linkage was found with > or =2 of these approaches on chromosomes 2, 4, 6, 7, 9, 14, and 21. The remaining linkage paper compared the utility of several single-nucleotide polymorphism (SNP) and microsatellite marker maps for Monte Carlo Markov chain combined oligogenic segregation and linkage analysis, and analyzed one of the electrophysiological endophenotypes, ttth1, on chromosome 7. Linkage was found with all marker sets. The last paper compared the multipoint IBD information content of several SNP sets and the microsatellite set, and found that while all SNP sets examined contained more information than the microsatellite set, most of the information contained in the SNP sets was captured by a subset of the SNP markers with approximately 1-cM marker spacing. From these papers, we highlight three points: a 1-cM SNP map seems to capture most of the linkage information, so denser maps do not appear necessary; careful and appropriate use of covariates can aid linkage analysis; and sources of increased gene-sharing between relatives should be accounted for in analyses.

Alcoholism↗

PubMed1994

Latent trait modelling of symptoms of schizophrenia.

Latent trait models were fitted to data for 149 schizophrenic or schizophreniform inpatients rated on the Scale for the Assessment of Positive Symptoms (SAPS) and the Scale for the Assessment of Negative Symptoms (SANS) using the Rasch Extended Logistic Model. It was found that a reduction in the numbers of rating categories, from six to three or four led to consistencies in response while deletion of several items led to consistent scales of symptoms that accorded with an item response characterization. Behaviours included in the final scales varied in the numbers of categories, and in the range of symptom level covered by a category. Relationships between scores representing symptoms were found to be modelled better by a factor structure that included a third overlapping 'cognitive' factor in addition to the now traditional positive and negative factors, than by the original positive and negative factors alone.

Adult↗

PubMed2005

Kinetic modeling of batch hydrogen production process by mixed anaerobic cultures.

The kinetics of batch anaerobic hydrogen production by mixed anaerobic cultures was systemically investigated in this study. Unstructured models were used to describe the substrate utilization, biomass growth and product formation in the hydrogen production process. The relationship between the substrate, biomass and products were also evaluated. Experimental results show that the Michaelis-Menten equation, Logistic model and modified Gompertz equation all could be adopted to respectively describe the kinetics of substrate utilization, biomass growth and product formation. Furthermore, the relationship between the acidogenic products and biomass was simulated by Luedeking-Piret model very well. The experimental results suggest that the formation of hydrogen and the main aqueous products, i.e., butyrate and acetate, was all growth-associated.

Acetates↗

PubMed1999

Indications and limits of ultrasound-guided cytology in the management of nonpalpable thyroid nodules.

Although ultrasound (US)-guided fine needle aspiration biopsy (FNAB) is widely prescribed in nonpalpable thyroid nodules, the goal of this study was to define precisely the indications and limits of US-FNAB in a series of 450 nonpalpable nodules. Among 94 surgically controlled cases, 20 (8 infracentimetric and 12 centimetric or supracentimetric) carcinomas were diagnosed. The diagnosis of malignancy was successfully made by US-FNAB in 16 of 20 carcinomas, 3 were missed because of insufficient cytological material, and 1 was misdiagnosed. US-FNAB sensitivity and specificity were 94% and 63%, respectively. A logistic model indicated that nodule size (P < 0.6) was not associated with histological diagnosis, but that solid hypoechoic features were more likely to be malignant (P < 0.0003), with US sensitivity and specificity for malignancy of 80% and 70%, respectively. Logistic regression indicated that adequate cytological material significantly increased with nodule size (P < 0.0001). This result outlined the limits of US-FNAB in small nodules. Hence, indication of US-FNAB appears judicious in centimetric or supracentimetric nodules or in solid and hypoechoic ones. Such a management would allow the discovery of 15 of 20 carcinomas and would avoid 16% of unnecessary biopsies.

Adolescent↗

PubMedDate not supplied

Accuracy of obesity diagnosis in Brazilian adolescents: comparison of Cole et al and Must et al criteria with DXA percentage of fat mass.

OBJECTIVES: to assess the accuracy of the two most used anthropometric criteria: Must and Cole to diagnose obesity in adolescence comparing with percentage of fat mass determined by DXA. METHODOLOGY: cross-sectional study with 418 adolescents (52.4% males) attending a private school in São Paulo/Brazil. Anthropometric measures of height and weight were taken and BMI was calculated. Analysis of body composition was performed using the DXA to detect percentage of fat mass. Using the method proposed by Ellis & Wong (ERM) two sex-specific linear regression models of fat percentage for age in years were fitted. The comparison between the methods was carried out through the analyses of specificity and sensitivity with two residual percentiles as cutoff points (ERM85th and ERM95th) as standards. A logistic model was fitted to estimate the probability curves of obesity classification. RESULTS: the comparison of the two classic criteria for the diagnosis of obesity with the ERM85th and ERM 95th, yields for females the same sensitivities of 0.50 and 0.20 for both criteria. For males sensitivities for ERM 85th were 0.61 (Must) and 0.49 (Cole); while for ERM95th the sensitivities were 0.81 (Must) and 0.64 (Cole). Therefore, there are high probabilities that those criteria diagnose adolescents as obese, when actually they are not. CONCLUSION: the Must and Cole criteria were similar and present flaws for the diagnosis of obesity. In clinical practice and field studies anthropometric criteria should be evaluated as to the diagnostic accuracy along with other clinical parameters and, when feasible, the analysis of fatness percentage. However, the anthropometric criteria evaluated are efficient in the identification of non-obese adolescent in the two cutoff points considered.

Absorptiometry, Photon↗

PubMed1989

Alternative models of the stress buffering hypothesis.

The interactive effects of life events and social support on a DSM-III diagnosis of major depressive episode and on number of depressive symptoms were examined. Data are from a stratified random sample of 3,732 community-dwelling adults. The paper focuses on differences between linear probability models and logistic regression models with regard to the definition, detection, and interpretation of interaction effects. Results indicate that conclusions about the interaction of life events and social support are model dependent. Using a linear probability model, significant event by support interactions were observed for both depressive symptoms and major depression. Using logistic regression, which estimates interactions in terms of odds ratios, no significant event by support interactions were observed. Discussion addresses the interpretive implications of modeling interaction in terms of probability differences versus odds ratios.

Adolescent↗

PubMed1989

Identification of an optimal subgroup for treatment evaluation of patients with brain metastases using RTOG study 7916.

The overall poor prognosis of brain metastases patients has complicated the evaluation of treatment effectiveness in previous clinical trials involving radiation therapy. Therapy has not been seen to alter survival, which is generally short in these patients. Possible benefits of the treatments tested may be better assessed using a favorable group of patients who are at lower risk of dying quickly from cancer. The determination of a patient subgroup having prolonged survival allows for improvement in the design and analysis of subsequent clinical trials. An optimal patient group was identified in an RTOG study (7916) that evaluated two fractionation schedules (30 Gy/10 fractions/2 weeks and 20 Gy/6 fractions/3 weeks) with or without the administration of misonidazole (MISO) in the treatment of brain metastases. A Cox regression model was used to identify the pretreatment characteristics associated with a favorable prognosis for survival: Karnofsky Performance Status (KPS) of 70-100, an absent/controlled primary tumor, age less than 60 years, and metastatic spread limited to the brain. A logistic model confirmed that the odds of surviving at least 200 days depend on these pretreatment characteristics. Patients with all four favorable characteristics constitute 11% of the evaluable study population and have a predicted 200 day survival of 52%. Prognostically favorable subgroups have been identified as patients having at least three of these four favorable characteristics. These patients have predicted probabilities of 200 day survival between 33 and 52%. Conversely, unfavorable subgroups are defined as patients having two or less favorable characteristics. Subsequent verification of these results by a second data set is warranted. The prognostically favorable characteristics have been used to define the patient population in a current RTOG study evaluating accelerated radiation therapy in patients with brain metastases.

Brain Neoplasms↗

PubMed1993

Pitfalls inherent in retrospective time-to-event studies: the example of time to pregnancy.

Retrospective studies of time from initiation of risk (for example, transfusion of HIV-infected blood) to the occurrence of an endpoint of interest are useful in epidemiology. One example is studies of time to pregnancy, which have evaluated exposures that may affect human fertility. One can reconstruct the non-contracepting interval required for each woman's most recent pregnancy and then treat the data as if the couples had been studied prospectively. As we illustrate, however, failure-time models can be dangerously misleading when there have been trends over calendar time in exposures under study. We propose an ad hoc method for evaluating possible effects on fertility despite this bias, by making use of external data on trends in the exposure over time. This approach applies a prospective model and generates an empirical p-value, based on comparing the data-based estimated exposure coefficient with its null distribution estimated by simulation. A second method maximizes a conditional likelihood, and we show that this is equivalent to logistically modelling the relative odds for the subject's exposure as related to the reported time she required to achieve pregnancy.

Bias↗

PubMed1987

Frequency, diagnosis and clinical characteristics of patients with multiple accessory atrioventricular pathways.

Multiple accessory atrioventricular (AV) pathways were documented in 52 of 388 patients (13%) who underwent detailed electrophysiologic evaluation. Multiple AV pathways were identified during intraoperative mapping or electrophysiologic study by different patterns of ventricular preexcitation during atrial fibrillation, flutter or atrial pacing with different delta-wave morphologic and ventricular activation patterns; different sites of atrial activation during right ventricular pacing or orthodromic reciprocating tachycardia; or preexcited reciprocating tachycardia using a second pathway as the retrograde limb of the tachycardia. A logistic model was used to determine which clinical, electrocardiographic and electrophysiologic variables were associated with multiple AV pathways. Right free-wall and posteroseptal accessory AV pathways were more common in patients with multiple AV pathways and were frequently associated. Multivariate logistic regression identified Ebstein's anomaly, and a history of preexcited reciprocating tachycardia as significant variables (p less than 0.0001). Pathway location was not subjected to statistical analysis because of confounding variables.

Adolescent↗

PubMed2002

Creating a scale to measure motivation to achieve academically: linking attitudes and behaviours using Rasch measurement.

BACKGROUND: Motivation to Achieve Academically has been used in many educational and other studies in many countries and the large majority has not used an interval level scale based on a good theoretical model in which the items are linked to behaviour. AIMS: One, to create an interval level, unidimensional scale of Motivation, with attitude items linked to behaviour items, based on a conceptual model of Motivation, involving Striving for Excellence (Standards, Goals, Tasks, Effort, Values and Ability), Desire to Learn (Interest, Learning from Others and Responsibility for Learning), and Rewards (Extrinsic, Intrinsic and Social). Two, to analyse its psychometric properties using the Extended Logistic Model of Rasch (Andrich, 1988a, 1988b; Rasch, 1980/1960). Three, to investigate the structure and meaning of the scale. SAMPLE: The convenience person sample was 239 first-year students selected for three special entry programmes at an Australian university. The stem-item sample was initially 45, reduced to 24, that fitted the measurement model to form a valid and reliable scale. METHOD: Based on recent literature, a conceptual model of Motivation was devised and items written in line with the model. Data were collected by self-report questionnaire and analysed with the computer program Rasch Unidimensional Measurement Models (RUMM) (Andrich, Lyne, Sheridan, & Luo, 1998). A scale was created in which the Motivation measures were calibrated on the same scale as the item 'difficulties'. RESULTS: Twenty-four Motivation items fitted the model and were 'easier' than their corresponding behaviour items, as conceptualised. They formed an excellent scale in which the proportion of observed variance considered true was 0.93. Items from all aspects of the Motivation model named in the aims above, except Ability and Extrinsic Rewards, fitted the measurement model. CONCLUSION: The Rasch model and the RUMM computing program were very useful in creating a unidimensional, interval level scale of Motivation to achieve academically, with good psychometric properties.

Achievement↗

PubMed2005

Surgical intervention for advanced valvular heart disease in 227 cases.

BACKGROUND: Although the results of surgical treatment in cardiac valve disease continue to improve, the postoperative mortality rate and the rate of complications in patients with advanced valvular heart disease (AVHD) are still very high. We did this retrospective study to summarize the surgical experience of heart valve replacement for patients with AVHD and discuss effective ways to improve the surgical outcome. METHODS: From January 1994 to October 2003, surgical procedures of heart valve replacement were performed on 227 (136 men and 91 women) patients with AVHD in our Department of Cardiothoracic Surgery. The clinical data of all patients were collected and analysed. Patients' age ranged from 10 years to 77 years. In preoperative cardiac function grading, 157 cases were NYHA III and 70 cases NYHA IV. Fifty-one patients had had cardiac operations. The ultrasonic cardiac graphs showed that 145 patients suffered from moderate or severe pulmonary hypertension and 73 had combined giant left ventricle. Mitral valve replacement was performed in 32 cases, aortic valve replacement in 90, tricuspid valve replacement in 1, combined mitral and aortic replacement in 103 and combined mitral and tricuspid replacement in 1. Nineteen patients also received surgical corrections for other minor abnormalities during the operations. A logistic model was established to evaluate the influence of perioperative factors on the mortality rate. RESULTS: The operative mortality rate was 13.2% (30/227). The main causes of death included multiple organ dysfunction syndrome (MODS), low cardiac output syndrome and ventricular fibrillation. From the results of the binary noncounterpart multivariate logistic regression, the following statistically significant factors were found to influence the operative mortality rate: redo operation, age >/= 55 years, preoperative NYHA cardiac function grading, extracorporeal circulation time >/= 120 minutes and postoperative usage of GIK (glucose, insulin and potassium) solution. All factors were risk ones except postoperative application of GIK. The Hosmer-Lemeshow goodness of fit coefficient of this model was 0.976. CONCLUSIONS: The risk factors associated with postoperative mortality rate in the patients with AVHD were redo operation, age >/= 55 years, preoperative NYHA cardiac function grading and extracorporeal circulation time >/= 120 minutes. Postoperative usage of GIK acted as a kind of metabolic therapy and will improve the recovery for patients with AVHD. Active perioperative management and care will play a very important role in reducing the operative risk and improving the short term outcome of surgical treatment for the patients with AVHD.

Adolescent↗

PubMed2000

Two-phase model of the kinetics of growth of Rhizopus oligosporus in membrane culture.

An empirical model was developed to describe a growth profile occurring in solid-state fermentation (SSF), namely that consisting of an initial period of rapid acceleration followed by an extended period of deceleration. This kinetic profile is not adequately described by the logistic model. The empirical model is based on the concept of active and nonactive hyphal segments. Exponential and deceleration growth phases are modeled. The model parameters can be determined directly from the dry-weight profile and they depend on the growth medium present. The model suggests that, at the instant the culture enters the deceleration phase, there is a 71% to 86% decrease in the number of actively extending hyphal tips and that, during the deceleration phase, there is an exponential decay in the number of active hyphal segments, with a first-order decay constant of 0.042 to 0.072 h(-1).

Biomass↗