Acidosis accentuates thiopental-induced myocardial depression in vitro.
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Acidosis↗
Biomedical subjects
G Maldonado
Publications and source records attributed to G Maldonado.
Impact of model-form selection on the accuracy of rate estimation.
A key assumption underlying the use of model-based estimates in epidemiology is that the structural-model form is an adequate mathematical description of the dependence of disease occurrence on exposures and covariates (that is, the model form is correctly specified). If this assumption is violated, model-based point estimators and variance estimators may be biased, standard confidence intervals may be invalid, and inferences derived from these estimators may be incorrect. In practice, the true structural-model form is usually unknown, and investigators frequently use their data to help select a model form. We conducted a simulation study to examine the impact of model-form selection on the accuracy of rate estimation in cohort-study situations resembling those found in environmental and occupational epidemiology. For the situations we examined, the increase in variance produced by using model-form selection was often more than offset by the corresponding reduction in bias, sometimes resulting in a dramatic increase in accuracy. Model-form selection was observed to be most beneficial relative to no selection when effects were stronger, the sample size was larger, and the candidate model forms included the true model form or allowed the model to more closely approximate the true model form. It was least beneficial when effects were weak and the sample size was small, even if the candidate model forms included the true model form.
Cohort Studies↗
The indoor air and children's health study: methods and incidence rates.
The Indoor Air and Children's Health Study is a prospective cohort study of the relation between indoor air pollution and lower respiratory illness (LRI) during the first 2 years of life. Information on family and household characteristics was obtained from a health maintenance organization for 1,424 infants enrolled at birth. Data on LRI were abstracted from medical records. The incidence of all LRI was 48.4 per 100 child-years. Wheezing-associated respiratory illness (WARI)/asthma was the most common specific LRI, with an incidence of 11.5 per 100 child-years. Total LRI incidence was lowest during the first 6 months of life. Girls had lower incidence than boys [rate ratio (RR) = 0.8; 95% confidence interval (CI) = 0.7-0.8)]. With the exception of croup, all LRI were most common during February and March. These results are comparable with those of other prospective studies. Consistent with other studies, self-reported maternal smoking demonstrated an RR of 1.5 (95% CI = 1.2-1.8) for total LRI, but the association varied for specific LRIs from 2.3 (95% CI = 1.5-3.0) for WARI/asthma to 1.0 (95% CI = 0.7-1.6) for bronchitis.
Air Pollution, Indoor↗
The state of the literature on primary care specialty choice: where do we go from here?
A large body of research on medical students' choice of primary care specialties has been published. However, the literature is difficult to interpret because of multiple biases, design weaknesses, small numbers of subjects, inconsistencies in both dependent and independent variables, and conflicting results. These weaknesses have been noted by authors who have reviewed the work in this area, but the authors have given little direction for ways to improve and build upon the current state of the literature. This paper provides a quantitative description of the content of the specialty choice literature. As part of a larger project that included an exhaustive literature analysis, all research on primary care specialty choice published between 1987 and 1993 was collected and summarized according to study questions, designs, data sources, samples, theory, and outcome variables. Portions of this information were used to rate the quality of each study, yielding a score from zero to 100 that indicated the trustworthiness of the study's conclusions. Overall, the studies examined were found to use predominantly cross-sectional designs and to lack theoretical basis. Special curricular tracks, student personality, and self-reported influences were the most frequently studied determinants of primary care specialty choices. The results confirm previous qualitative descriptions of the state of the literature on specialty choice, and lead to recommendations for approaches to improve the quality of further work in this area. The research agenda that emerged from the larger project is also presented.
Career Choice↗
Mammogram utilization among farm women.
Utilization of preventive health care services is lower in rural populations than in urban populations, possibly as a result of barriers to preventive health care that are characteristic of rural settings. This study was conducted to identify factors associated with mammogram utilization among farm women. Mammogram utilization among farm women from six southern Minnesota counties was examined as part of a larger community-based cancer intervention study. Farm women aged 40 and older were randomly selected from a list of farm households and interviewed by telephone to determine mammogram utilization and factors related to utilization. Of the 606 respondents, 78 percent reported ever having a mammogram and 49 percent reported a mammogram within the past year. Physician recommendation for a screening mammogram and family history of breast cancer were found to be associated with ever having a mammogram. Correct knowledge of mammogram screening guidelines was associated with a mammogram within the past 12 months. Overall, physician recommendation was the most influential determinant of utilization. As more emphasis is placed on prevention, patient education by physicians can have the greatest impact on mammogram utilization.
Agriculture↗
[Comparative study of HELISAL T.M. RAPID BLOOD and ELISA, JATROX and pathologic anatomy in the diagnosis of Helicobacter pylori infection].
OBJECTIVES: To assess the usefulness of HELISAL in the diagnosis of Helicobacter pylori infection by comparing it with ELISA, JATROX and histopathologic findings. EXPERIMENTAL DESIGN: Randomized prospective study. PATIENTS: Sixty-one patients, thirty-three males and twenty-eight females, 18-73 years old, submitted to esophagogastroduodenoscopy. RESULTS: The sensitivity of HELISAL when compared to ELISA test was 60.8%, the specificity 73.3%, the positive predictive value 87.5%, the negative predictive value 37.9%, and the kappa index 0.26. When compared to histopathologic test: sensitivity 60.9%, specificity 65%, positive predictive value 78.1%, negative predictive value 44.7%, kappa 0.28. When compared to JATROX, sensitivity 57.7%, specificity 62.5%, positive predictive value 81.2%, negative predictive value 34.4%, kappa 0.21. CONCLUSION: The sensitivity of HELISAL test is lower than that of other compared tests, and the negative predictive value is very low. The specificity and the positive predictive value are higher than the sensitivity. The kappa index shows a very low concordance.
Adult↗
Determinants of primary care specialty choice: a non-statistical meta-analysis of the literature.
This paper analyzes and synthesizes the literature on primary care specialty choice from 1987 through 1993. To improve the validity and usefulness of the conclusions drawn from the literature, the authors developed a model of medical student specialty choice to guide the synthesis, and used only high-quality research (a final total of 73 articles). They found that students predominantly enter medical school with a preference for primary care careers, but that this preference diminishes over time (particularly over the clinical clerkship years). Student characteristics associated with primary care career choice are: being female, older, and married; having a broad undergraduate background; having non-physician parents; having relatively low income expectations; being interested in diverse patients and health problems; and having less interest in prestige, high technology, and surgery. Other traits, such as value orientation, personality, or life situation, yet to be reliably measured, may actually be responsible for some of these associations. Two curricular experiences are associated with increases in the numbers of students choosing primary care: required family practice clerkships and longitudinal primary care experiences. Overall, the number of required weeks in family practice shows the strongest association. Students are influenced by the cultures of the institutions in which they train, and an important factor in this influence is the relative representation of academically credible, full-time primary care faculty within each institution's governance and everyday operation. In turn, the institutional culture and faculty composition are largely determined by each school's mission and funding sources--explaining, perhaps, the strong and consistent association frequently found between public schools and a greater output of primary care physicians. Factors that do not influence primary care specialty choice include early exposure to family practice faculty or to family practitioners in their own clinics, having a high family medicine faculty-to-student ratio, and student debt level, unless exceptionally high. Also, students view a lack of understanding of the specialties as a major impediment to their career decisions, and it appears they acquire distorted images of the primary care specialties as they learn within major academic settings. Strikingly few schools produce a majority of primary care graduates who enter family practice, general internal medicine, or general practice residencies or who actually practice as generalists. Even specially designed tracks seldom produce more than 60% primary care graduates. Twelve recommendations for strategies to increase the proportion of primary care physicians are provided.
Age Distribution↗
A systematic approach to conducting a non-statistical meta-analysis of research literature.
Literature analyses and syntheses are becoming increasingly important as a means of periodically bringing coherence to a research area, contributing new knowledge revealed by integrating single studies, and quickly informing scientists of the state of the field. As a result, there is a need for approaches that can provide replicable, reliable, and trustworthy results. Over the last decade many researchers have begun using the statistical meta-analysis approach to integrate studies. However, the single studies conducted in many areas are not of the type amenable to statistical meta-analysis but are more appropriate for non-statistical analysis and synthesis. The present paper describes (1) a rigorous approach to conducting a non-statistical meta-analysis of research literature and (2) an example of how this approach was applied to the literature of determinants of primary care specialty choice published between 1987 and 1993. This approach includes model development, literature retrieval, literature coding, rating references for quality, annotating high-quality references, and synthesizing only the subset of the literature found of sufficient quality to be considered. Also, the basic results of each included study are reported in the synthesis so that readers have before them all the "data points" used in the synthesis. Thus, readers can draw their own interpretations without having to re-collect the data, just as they would be able to do in any single study that presents original data as well as conclusions and discussion.
Meta-Analysis as Topic↗
Fatal farm injuries: a five-year study utilizing a unique surveillance approach to investigate the concordance of reporting between two data sources.
The agricultural industry has been ranked among the most hazardous. Yet, it has been alleged that occupational injuries and fatalities are seriously underreported. Access to quality agricultural injury data poses a special problem. The purpose of this study was to investigate the concordance of reporting of fatal agricultural injuries between death certificate data and the Newspaper Clipping Service data in the state of Minnesota, utilizing a surveillance system developed by the University of Minnesota. Between September 1, 1981, and August 31, 1986, a total of 350 agricultural fatalities were identified in Minnesota; 82% were identified through death certificate data and 67% through the Newspaper Clipping Service. Differences in reporting between the two data sources were noted for gender, age, injury type, anatomical site, source, mechanism of injury, and multiple versus single injury. If only death certificates had been utilized, 18% of the fatalities would have been missed. Although it is apparent that death certificate data have an advantage over the Newspaper Clipping Service data for fatality reporting of specific variables, this study revealed that death certificate surveillance alone will miss mortality data and detection of certain potential risk factors. Suggestions for improving surveillance of agricultural fatalities are identified. However, until relevant changes are made, it will be essential to use a combination of data sources that include the Newspaper Clipping Service to identify agricultural injury fatalities accurately.
Accidents, Occupational↗
Occupational exposure to inhalable and total aerosol in the primary nickel production industry.
OBJECTIVES: This paper describes a study that was carried out in the primary nickel production industry to investigate the levels of personal exposure to aerosols containing nickel and the impact on exposure assessment of introducing new personal sampling techniques with performance consistent with the latest particle size-selective criteria. METHODS: Experiments were carried out at workplaces in mining, milling, smelting, and refining works to investigate the effect of changing from the current method of total aerosol (with the widely used 37 mm filter holder) to the new method of measuring inhalable aerosol (with the Institute of Occupational Medicine (IOM) inhalable aerosol sampler). RESULTS: The results show that inhalable aerosol exposure concentrations--for both overall aerosol and for total nickel--were consistently and significantly higher than the corresponding total aerosol concentrations. Weighted least squares linear regression yielded IOM/37 mm factors ranging from about 1.2 to 4.0. The exposure data for each company process were found to be log-normally distributed. CONCLUSIONS: The results suggest the possibility of generating a single pragmatic factor for each company process for converting current total aerosol exposures to new exposures based on the inhalability concept contained in the latest particle size-selective criteria for aerosol exposure assessment. Such data may be important in determining new occupational exposure limits for nickel.
Aerosols↗
[Coronary angioplasty in patients with restenosis. Characterization of clinical and angiographic profiles, hospital clinical course, and implications for the selection of patients].
PURPOSE: To define the clinical and angiographic profile of patients undergoing to a 2nd or a 3rd coronary angioplaty (PTCA) for the treatment of restenosis, and assess the safety and efficacy of redilatation. METHODS: Patients submitted to PTCA for a 1st (1stRE) or a 2nd (2ndRE) restenosis, from Jan/1980 through Dec/1993, were retrospectively identified, and compared to those undergoing to PTCA for de novo lesions (DN). RESULTS: A total of 5,736 underwent to dilatation of primary lesions, 610 of a 1stRE, and 64 of a 2ndRE. Patients with restenotic lesions had a higher prevalence of diabetes, smoking, history of prior infarction (1stRE e 2ndRE) and hyperlipidemia (2ndRE) as compared with primary lesions (p < 0.05). Besides patients with a 2ndRE had a higher incidence of left ventricular dysfunction, as compared to those with DN or a 1stRE (31.3% with EF < 45% in group 2ndRE, vs 19.8% and 23.1% in groups 1stRE and DN, respectively, p < 0.05). Primary success, infarct rate and mortality were similar in all groups, but emergency bypass surgery was significantly higher in the DN (2.1% vs 0.8% in 1stRE and 0% in 2ndRE, p < 0.05). CONCLUSION: Restenosis can be effectively treated by redilatation. Patients with clinical and angiographic features predisposing to further recurrence can be better treated with other interventions (i.e., coronary stents, bypass surgery).
Angioplasty, Balloon, Coronary↗
[Impact of the Hospital Coordinator Program on obtaining kidneys for renal transplantation].
Limited organ supply is currently the major obstacle to the transplantation programs around the world. As an alternative to increase the organ donation rate, we undertook a preliminary transplant coordinator program study, during a 6 month period, in five public hospitals, as part of the National Transplant Program of the Centro Nacional de Diálisis y Trasplante. The primary objective of the Transplant Coordinator Program was donor detection and organ procurement, along with education of the community. Forty five predonors were detected, with an average age of 25.8 +/- 1.6 years, of these, 36 were men (80%). None of them was a voluntary donor. The most frequent diagnoses were cranial trauma in 57.8% and stroke in 22.2% Forty two percent (42.3%) of the predonors were detected in the emergency room, 33.3% in intensive care units and 24.4% in the surgery recovery room. The conversion rate of predonors to donors were 29%. The main causes for not conversion of predonors into donors were: family refusal 44%, sepsis 13%, cardiac arrest 13%, and reduced renal function 6%. In conclusion, the Transplant Coordinator Program allows to increase the predonor detection and gives good information for adequate management of donor and public educational campaign about the subject.
Adult↗
The interpretation of multiplicative-model parameters as standardized parameters.
Under current conventions, relative-risk estimates obtained from multiplicative models are interpreted as estimates of a homogeneous effect. Such interpretations condition on the unverifiable assumption that the relative risk under study is homogeneous, an assumption that is not likely to be correct even if the model fits well. We propose that such estimates are better interpreted as estimates of standardized relative risks, with a bias component that depends on the degree of model misspecification and on the study design. To evaluate our proposal, we present a study of the maximum-likelihood estimators from Poisson and logistic regression compared to the population-standardized rate ratio. The results indicate that our proposed interpretation would in practice be more cautious and accurate than the homogeneous-effect interpretation.
Case-Control Studies↗
An epidemiologic study of carpal tunnel syndrome and hand-arm vibration syndrome in relation to vibration exposure.
No Minnesota workers' compensation claims have been filed for permanent partial disability benefits with a diagnosis of hand-arm vibration syndrome (HAVS). A cross-sectional study was undertaken to evaluate 519 compensation claimants following carpal tunnel surgery. Workers with significant vibration exposure and symptoms compatible with HAVS were identified within the group. The results show that some workers are not diagnosed as having HAVS even though they meet the diagnostic criteria. This suggests that HAVS should be considered in the differential diagnosis when a worker presents with neural and/or vascular symptoms of the hands and fingers.
Adolescent↗
A comparison of the performance of model-based confidence intervals when the correct model form is unknown: coverage of asymptotic means.
We conducted a simulation study to examine the performance of confidence intervals when multiplicative and additive rate (Poisson regression) models are fit to follow-up data, but the model form may be misspecified. Data were generated from over 129,000 different population structures that ranged from sub-additive to supra-multiplicative. When a multiplicative model was fit, all of the confidence intervals that we examined performed well as interval estimators of the asymptotic means of the point estimators, even when the correct model form was not multiplicative. When an additive model was fit, (1) only the likelihood ratio interval and the score interval with expected information consistently performed well, and they consistently performed better than any of the Wald intervals that we examined; (2) Wald intervals performed better when calculated with observed information rather than with expected information; and (3) Wald intervals with expected information performed better when the information matrix was evaluated at the restricted maximum likelihood estimate rather than the unrestricted maximum likelihood estimate.
Confidence Intervals↗
Effect of lectins on mouse peritoneal macrophage phagocytic activity.
We studied the in vitro ability of lectin-treated murine peritoneal macrophages to attach and phagocytize particulate antigens. Glucose and mannose specific lectins such as Con-A and lentil lectin, as well as complex lactosamine residues specific lectins, such as Phaseolus vulgaris var. cacahuate and Phaseolus coccineus var. alubia, increased the macrophage phagocytic activity towards heterologous erythrocytes, whereas peanut agglutinin, a galactose-specific lectin, diminished the macrophage phagocytic activity. These results suggest that a galactose-N-acetyl-D galactosamine-containing structure could participate as negative modulator of the phagocytic activity.
Acetylgalactosamine↗
Simulation study of confounder-selection strategies.
In the absence of prior knowledge about population relations, investigators frequently employ a strategy that uses the data to help them decide whether to adjust for a variable. The authors compared the performance of several such strategies for fitting multiplicative Poisson regression models to cohort data: 1) the "change-in-estimate" strategy, in which a variable is controlled if the adjusted and unadjusted estimates differ by some important amount; 2) the "significance-test-of-the-covariate" strategy, in which a variable is controlled if its coefficient is significantly different from zero at some predetermined significance level; 3) the "significance-test-of-the-difference" strategy, which tests the difference between the adjusted and unadjusted exposure coefficients; 4) the "equivalence-test-of-the-difference" strategy, which significance-tests the equivalence of the adjusted and unadjusted exposure coefficients; and 5) a hybrid strategy that takes a weighted average of adjusted and unadjusted estimates. Data were generated from 8,100 population structures at each of several sample sizes. The performance of the different strategies was evaluated by computing bias, mean squared error, and coverage rates of confidence intervals. At least one variation of each strategy that was examined performed acceptably. The change-in-estimate and equivalence-test-of-the-difference strategies performed best when the cut-point for deciding whether crude and adjusted estimates differed by an important amount was set to a low value (10%). The significance test strategies performed best when the alpha level was set to much higher than conventional levels (0.20).
Bias↗
Interpreting model coefficients when the true model form is unknown.
In this paper, we critically examine mathematical modeling. We outline the major assumptions required by modeling methods used in epidemiology and discuss in detail one fundamental assumption that is usually violated in epidemiologic studies: the assumption that the structural model form is correctly specified. We apply concepts from the econometrics literature to examine how epidemiologic inference may be affected when the structural model form is incorrectly specified. Because the structural model is almost always misspecified in practice, tests and confidence intervals for model coefficients do not refer to "true population parameters" in the ordinary sense. Rather, these statistics concern parameters that depend on features of study design, as well as the effects under study. In cohort studies analyzed with multiplicative rate models, model parameters are interpretable as approximations to log standardized rate ratios; unfortunately, such interpretations are not as accurate for other models and designs. We therefore conclude that model coefficients can serve as reasonable effect summaries in some, but not all, situations.
Bias↗