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At least 127 records · Page 7Linked to original sources
PubMed2000

Biases in ecological studies: utility of including within-area distribution of confounders.

This paper is centred on studies commonly known as ecological studies, where one seeks to estimate risks from data aggregated on a geographical basis. The aggregated nature of the data creates difficulties for interpreting, at an individual level, any ecological association found, difficulties which are generically referred to as 'the ecological bias or fallacy'. Here, we address an important component of this bias related to the problem of misspecification in ecological studies. We consider how aggregated level dose-response relationships are derived from integrating individual level ones over the group, and how their correct specification requires, in general, knowledge of the within-group joint distribution of the relevant risk factors, which is rarely available. We discuss in detail the common situation where data on the proportion of persons exposed in each area to several dichotomous risk factors are available. We show that ecological regression estimates of the relative risk for each factor will be improved by including in the regression, besides the linear terms, cross-product terms of the marginal prevalences. Results from a simulation study are discussed and an example concerning the geographical analysis of lung cancer mortality in France is presented.

Adult↗
PubMed1990

Temporally intensive study of trace metals in sediments and bivalves from a large river-estuarine system: Suisun Bay/Delta in San Francisco Bay.

Distributions in time and space of Ag, Cd, Cr, Cu, Pb and Zn were determined in fine-grained sediments and in the filter-feeding bivalve Corbicula sp. of Suisun Bay/delta at the mouth of the Sacramento and San Joaquin Rivers in North San Francisco Bay. Samples were collected from seven stations at near-monthly intervals for 3 years. Aggregated data showed little chronic contamination with Ag, Zn and Pb in the river and estuary. Substantial chronic contamination with Cd, Cu and Cr in Suisun Bay/delta occurred, especially in Corbicula, compared with the lower San Joaquin River. Salinity appeared to have secondary effects, if any, on metal concentrations in sediments and metal bioavailability to bivalves. Space/time distributions of Cr were controlled by releases from a local industry. Analyses of time series suggested substantial inputs of Cu might originate from the Sacramento River during high inflows to the Bay, and Cd contamination had both riverine and local sources. Concentrations of metals in sediments correlated with concentrations in Corbicula only in annually or 3-year aggregated data. Condition index for Corbicula was reduced where metal contamination was most severe. The biological availability of Cu and Cd to benthos was greater in Suisun Bay than in many other estuaries. Thus small inputs into this system could have greater impacts than might occur elsewhere; and organisms were generally more sensitive indicators of enrichment than sediments in this system.

Animals↗
PubMed2004

Community-acquired pneumonia mortality: a potential link to antibiotic prescribing trends in general practice.

BACKGROUND: Community prescribing of antibiotics has decreased substantially in the UK in recent years. We examine the association between pneumonia mortality and recent changes in community-based antibiotic prescribing for lower respiratory tract infections (LRTI). METHODS: Retrospective analysis of aggregated data for pneumonia mortality, influenza incidence, and antibiotic prescribing for LRTI in England and Wales during 12-week winter periods between 1993/94 and 1999/2000. RESULTS: Winter antibiotic prescribing for LRTI showed a 30.0% decline since 1995/96. Over the same period, there was a 50.6% increase in winter excess pneumonia mortality adjusted for influenza incidence. Negative binomial regression analysis showed that the incidence of influenza alone had a significant association with winter pneumonia mortality (P<0.001). The analysis also showed the reduction in antibiotic prescribing had a small but significant association with mortality (P<0.001), when simultaneously modelling for influenza incidence. CONCLUSIONS: Our findings suggest an association between recent reductions in antibiotic prescribing for LRTI in general practice and an increase in pneumonia mortality in England and Wales. This retrospective study of aggregate data represents the first attempt to assess the effect of limiting antibiotic prescribing on patient outcomes, and highlights the need to identify which patients benefit from antibiotic treatment for LRTI.

Anti-Bacterial Agents↗
PubMed1983

Alcohol consumption and ischemic heart disease mortality: are time-series correlations meaningful?

Recently, time-series correlations of aggregated data have been used to demonstrate the length of latency periods for environmental factors, such as economic conditions and alcohol consumption, in influencing heart disease mortality. Latency periods were specified by lagging mortality rates relative to the economic indicators or rates of alcohol consumption until the highest correlations were achieved. The tendency has been to interpret these correlations without regard to whether the latency periods described are biologically plausible. The authors have identified four models which represent all the possible outcomes of correlational studies of time-series data. Using United States and Canadian mortality rates in relationship to alcohol consumption, they have demonstrated the application of each of these models. For three of the four models, the time-series (lag) correlations are uniform regardless of the number of years mortality is lagged relative to alcohol consumption, and this uniformity does not permit a latency period to be identified. Only the lag correlations between two nonlinear variables show variations over time, depending on the degree of correspondence between the increasing and decreasing line segments of the two curves. Correlations ranging from high positive to high negative are possible, and several peak correlations (positive and negative) can occur. However, the biologic interpretation of multiple peaks with the same or different signs is problematic. The authors conclude that time-series correlations of aggregated data are not useful for the study of latency periods, and that analysis of time-series correlations for this purpose can be at best ambiguous, and at worst, completely misleading.

Adolescent↗
PubMedDate not supplied

Influence of social factors on avoidable mortality: a hospital-based case-control study.

OBJECTIVE: The effect of socioeconomic factors on avoidable mortality at an individual level is not well known, since most studies showing this association are based on aggregate data. The purpose of this study was to determine socioeconomic differences between those patients who die of avoidable causes and those who do not die. METHODS: A matched case-control study was carried out regarding in-hospital avoidable mortality (Holland's medical care indicators) that occurred in a university hospital serving a Spanish-Mediterranean population during a 30-month period. RESULTS: We studied 82 cases of death from avoidable causes and 300 controls matched on medical care indicators and age. The variables that showed a statistically significant association with in-hospital avoidable mortality were number of diagnoses (the greater the number, the higher the risk), length of stay (patients staying seven or more days presented a lower risk), and education. Those patients with low and middle educational levels showed a greater risk of avoidable mortality (adjusted odds ratio=3.57 and 2.82, respectively) than those patients with higher levels of education. CONCLUSIONS: Consistent with the findings of studies based on aggregate data, our case-control analyses indicated that among several socioeconomic variables studied, educational level was significantly associated with the risk of in-hospital avoidable mortality, regardless of age and medical care indicators. Patients with low levels of education (<6 years of schooling) were at highest risk for in-hospital avoidable mortality, followed by those with middle levels of education (7-10 years of schooling).

Adolescent↗
PubMed1992

Variations in the use of cesarean delivery for dystocia: lessons about the source of care.

Aggregate data show variations in the use of cesarean delivery according to the source of care, which suggests that rising cesarean rates are at least in part attributable to nonmedical factors. In the research presented here, the likelihood of cesarean delivery is examined for low-risk, primiparous women with physicians who practice in a single hospital but are from three practice organizations--a health maintenance organization (HMO), private practice, and a hospital clinic--while controlling for a wide spectrum of clinical factors. Maternal age was found to be a dominant factor in determining the decision for a cesarean delivery, independent of clinical risk and physicians' practice organization. Only among women in their optimal childbearing years (25 to 29 years) was having an HMO physician associated with a lower likelihood of cesarean delivery. The authors conclude that lowering the primary cesarean rate in the 1990's may require more reeducation and clinical policy formulation, with particular attention being paid to maternal age, and less reorganization of services than the aggregate data suggests.

Adult↗
PubMed2002

Infant mortality in India: use of maternal and child health services in relation to literacy status.

Slow reduction in infant mortality rate in the last couple of decades is a major concern in India. State-level aggregate data from the National Family Health Survey 1992 and micro-level data on rural mothers (n=317) were used for examining the influence of female literacy on reduction of infant mortality through increased use of maternal and child health (MCH) services. Illiteracy of females was strongly associated with all variables relating to maternal care and also with infant mortality rate. States were grouped into best, medium, and worst on the basis of female illiteracy (about 11%, 48.5%, and 75% respectively). Infant mortality rate (per 1,000 livebirths) was significantly (p<0.01) higher among the worst group (90.99) than that among the medium (64.2) and the best (24.0) groups. Use of maternal health services increased in the worst to become the best groups for tetanus toxoid (from 48.0% to 84.4%), iron and folic acid tablets (36.6% to 76.2%), hospitalized deliveries (14.2% to 69.7%), and childcare services, such as vaccination (23.8% to 64.9%). Illiteracy of females had a more detrimental impact on rural than on urban areas. In the event of high female illiteracy, male literacy was beneficial for improving the use of services for reducing infant mortality rate. The micro-level study supported all major findings obtained for the national-level aggregate data. Programmes, like providing free education to girls, will yield long-term health benefits.

Child↗
PubMed1998

Multi-level modelling of geographically aggregated health data: a case study on malignant melanoma mortality and UV exposure in the European Community.

A multi-level modelling approach is used to examine the variance in mortality rates from malignant melanoma at different geographical scales within nine European nations with reference to exposure to ultraviolet light (UVB). For males and females, the greatest variations in the relationship between UVB exposure and mortality are seen between nations, rather than regions and sub-regions within nations. This suggests that factors and characteristics acting at a national scale, such as genetic and behavioural differences, are of importance. Multi-level modelling is used to show how a previous suggestion of a quadratic association between UVB exposure and malignant melanoma across Europe is unlikely to be true. The general usefulness of multi-level modelling in the analysis of disease data which is structured in a hierarchy is discussed, with particular reference to geographical analyses of small area data.

Climate↗
PubMed2005

Liver transplantation for severe hepatic graft-versus-host disease: an analysis of aggregate survival data.

Graft-versus-host disease (GVHD) often occurs after bone marrow transplantation (BMT). GVHD may lead to cirrhosis or complete destruction of the bile ducts, and few effective treatment options exist for such cases. Orthotopic liver transplantation (OLT) has been described as an option, but to date the patient survival, graft survival, and GVHD recurrence rates after OLT have been unknown. Cases of OLT for GVHD were accumulated from several sources: (1) cases of OLT performed at a single institution, (2) the English-language medical literature, and (3) the United Network for Organ Sharing (UNOS) liver transplant registry. Descriptive data were derived from pre- and post-OLT information; survival analysis was performed using the Kaplan-Meier method. One case of OLT for GVHD after BMT was found at our institution, and another 6 cases were previously reported in the literature. Extrahepatic GVHD recurred in 2 cases, but no recurrence of hepatic GVHD was reported. The UNOS registry contained an additional 73 patients who underwent OLT for hepatic GVHD. The 1- and 5-year actuarial patient survival rates were 72.4% and 62.9%, respectively. Although 4 patients required retransplantation, no deaths or retransplants were attributed to the recurrence of hepatic GVHD. OLT is an effective treatment for hepatic GVHD after BMT or non-liver organ transplant. Long-term disease-free survival is obtainable in these cases, and recurrence of hepatic GVHD has not been reported. These findings suggest that OLT should be considered as an effective treatment option for cases of hepatic GVHD recalcitrant to medical treatment.

Adolescent↗
PubMed1993

A method for selecting data subsets from large medical data bases.

Because of the exponential increase in health care expenditures, attention has been drawn to the cost and effectiveness of health care delivered. The use of electronic data bases as a means for assessing health care effectiveness has been advocated as powerful computer systems have become commonplace. The need to work efficiently with extremely large data bases presents difficult challenges to researchers who wish to focus on specific aspects of the data. This paper describes a computer program written to facilitate the analysis of large medical data sets by providing a straightforward way to specify and select data subsets from the aggregate data base.

Centers for Medicare and Medicaid Services, U.S.↗
PubMed1999

staffTRAK-TB: software for surveillance of tuberculosis infection in healthcare workers.

The Centers for Disease Control and Prevention (CDC) recommends periodic tuberculin skin testing of healthcare workers with potential exposure to Mycobacterium tuberculosis. However, many healthcare facilities have neither a system to identify workers due for their skin test nor a means of analyzing aggregate data. To illustrate some of the complexities involved in tuberculin skin test (TST) tracking and analysis, and how these might be addressed, this report describes a software package called staffTRAK-TB, developed by the CDC to facilitate surveillance of tuberculosis infection in healthcare workers. staffTRAK-TB records data for each healthcare worker, including demographic information, occupation, work location, multiple TST results, and results of evaluations to determine if clinically active tuberculosis is present. Programmed reports include lists of workers due and overdue for skin tests, and skin test conversion rates by occupation or worksite. Standardization of types of occupations and locations allows data from multiple facilities to be aggregated and compared. Data transfer to the CDC can be performed via floppy diskettes. staffTRAK-TB illustrates important issues in software structure, standardization of occupation and work-location information, relevant data items, and reports and analyses that would be useful in practice. Developing software that adequately addresses the epidemiological issues is complex, and the lessons learned may serve as a model for hospital epidemiologists, infection control personnel, occupational health personnel, and computer programmers considering software development in this area or trying to optimize their facility's TST surveillance.

Adult↗
PubMed1996

Lower consumption of wine and fish as a possible explanation for higher ischaemic heart disease mortality in Spain's Mediterranean region.

BACKGROUND: There is an apparent paradox in the geographical distribution of ischaemic heart disease (IHD) mortality in Spain. The Mediterranean regions, those with the lowest consumption of total and saturated fats, register the highest mortality due to IHD. This paper seeks to explain this paradox by examining the provincial distribution of IHD mortality in Spain and their known risk factors, dietetic and non-dietetic. METHODS: The study was based on data aggregated by province. Mortality data were taken from official vital statistics, while data on diet and other lifestyle habits were obtained from representative, large-scale, sample-based population surveys. Correlation and multiple regression analyses were run on standardized IHD mortality ratios for the period 1983-1987 and potential dietetic and non-dietetic determinants in 1989-1981. RESULTS: Intake of total lipids, saturated and polyunsaturated fatty acids, fish and wine were lower in Spain's southern and eastern provinces. Consumption of wine, fish, chicken, dairy products, vegetables and blond cigarettes, as well as unemployment, explained 53% of the variation in IHD mortality. Consumption of fish and wine alone exhibited a statistically significant relationship (P < 0.05) with IHD mortality. Moderate consumption of wine was negatively associated with IHD mortality, whereas heavy consumption patterns revealed a positive association. CONCLUSIONS: Based on correlation analyses of ecological data, lower consumption of wine and fish may explain the apparent paradox of higher IHD mortality in the presence of a lower intake of saturated fats in Spain's Mediterranean regions.

Aged↗
PubMedDate not supplied

Developing performance measures for sedation and analgesia: the approach of the Quality Indicator Project.

This article describes the development of a set of measures focused on use of and complications following sedation and analgesia. This group of measures is another step in a 15-year quest of a group of hospitals and other healthcare providers to identify ways to better monitor and understand performance--and thereby improve their ability to identify opportunities for improvement. The article describes in detail the practical steps taken to develop, test, and implement the measures, as well as some of the fundamental conceptual issues associated with cost and benefits of performance measurement. Finally, it examines the pilot-test experience for the measures--both the individual hospitals' efforts to implement data collection and the aggregate data that resulted from the pilot test.

Ambulatory Surgical Procedures↗
PubMed2003

Patient age and outcome following severe traumatic brain injury: an analysis of 5600 patients.

OBJECT: Increasing age is associated with poorer outcome in patients with closed traumatic brain injury (TBI). It is uncertain whether critical age thresholds exist, however, and the strength of the association has yet to be investigated across large series. The authors studied the shape and strength of the relationship between age and outcome, that is, the 6-month mortality rate and unfavorable outcome based on the Glasgow Outcome Scale. METHODS: The shape of the association was examined in four prospective series with individual patient data (2664 cases). All patients had a closed TBI and were of adult age (96% < 65 years of age). The strength of the association was investigated in a metaanalysis of the aforementioned individual patient data (2664 cases) and aggregate data (2948 cases) from TBI studies published between 1980 and 2001 (total 5612 cases). Analyses were performed with univariable and multivariable logistic regression. Proportions of mortality and unfavorable outcome increased with age: 21 and 39%, respectively, for patients younger than 35 years and 52 and 74%, respectively, for patients older than 55 years. The association between age and both mortality and unfavorable outcome was continuous and could be adequately described by a linear term and expressed even better statistically by a linear and a quadratic term. The use of age thresholds (best fitting threshold 39 years) in the analysis resulted in a considerable loss of information. The strength of the association, expressed as an odds ratio per 10 years of age, was 1.47 (95% confidence interval [CI] 1.34-1.63) for death and 1.49 (95% CI 1.43-1.56) for unfavorable outcome in univariable analyses, and 1.39 (95% CI 1.3-1.5) and 1.46 (95% CI 1.36-1.56), respectively, in multivariable analyses. Thus, the odds for a poor outcome increased by 40 to 50% per 10 years of age. CONCLUSIONS: An older age is continuously associated with a worsening outcome after TBI; hence, it is disadvantageous to define the effect of age on outcome in a discrete manner when we aim to estimate prognosis or adjust for confounding variables.

Adult↗