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PubMed1992

Epidemiological typing methods for mycoses.

Despite the increasing importance of nosocomial fungal infections, very little is known of the epidemiology, mode of transmission, or pathogenesis of infections due to fungal pathogens. Recently, a number of potentially useful epidemiological typing systems have been employed for identification of strains within species of Candida and other fungi. Epidemiological studies employing either DNA-based or protein-based typing methods have provided some interesting insights into the epidemiology of nosocomial fungal infections, particularly nosocomial candidiasis. Careful epidemiological studies employing selected typing methods are essential to the rational development of effective measures for prevention and control of nosocomial infections caused by opportunistic fungal pathogens.

Candida↗
PubMed1990

[The indications for the use of different statistical methods of epidemiological analysis and delimitation in the assessment of a dynamic epidemic process].

To solve various problems connected with epidemiological analysis concerning evaluation of the level, direction and intensity of the time course of the epidemic process and character of the cyclic component, the indications and limitations to the use of the following statistical methods have been worked out: equalizing by the method of the least squares on a straight line, a parabola, an exponential or power curve; calculation of the average annual rate of increase; leveling of dynamic series by the methods of internal prolongation, sliding and suspended sliding mean values; calculation of deviations from the theoretical tendency line; autocorrection. 11 computer programs have been compiled on the basis of the algorithms of the above methods, complete with the service menu, for the program complex "Epidanalysis" which permits an epidemiologist to proceed from the problem via indications and limitations to the adequate statistical method and the corresponding software. The programs are intended for different types of computers (EC-1840, Robotron 1715, IBM PC XT).

Algorithms↗
PubMed1999

Statistical methods for epidemiologic studies of the health effects of air pollution.

We describe two statistical designs that can provide efficient estimates of the health effects of exposure to air pollutants in epidemiologic studies. We also evaluate the effects of measurement error in exposure assessment on the accuracy of estimated health effects. The bidirectional case-crossover design is a variant of a method proposed by Maclure (1991). Our version of the method takes advantage of the fact that in epidemiologic studies involving environmental exposure, accurate information about past exposure is more readily available, and that levels of exposure are generally unaffected by the response of the subject. It differs from other case-crossover methods in that control information is assessed both before and after failure, thus avoiding confounding due to time trends in exposure. The multilevel analytic design provides a method of combining estimates of health effects made on the individual level with those made at the group level. It has great potential value in situations where variations in exposure within groups may not be great enough to provide adequate power to detect health effects, as is often the case in air pollution studies where exposure levels are similar within a geographic community. Measurement errors in exposure assessment can have substantial impact on the accuracy of estimated health effects. When the microenvironmental approach is used to estimate exposure, a standard error of 30% in estimating indoor/outdoor ratios can increase the standard error of a relative risk estimate by 50%, and introduce bias as well. Similar results hold when exposure is estimated with personal samplers. When the microenvironmental approach is used, errors in estimating indoor/outdoor ratios have more influence on the accuracy of risk estimation than do errors in estimating the time spent in microenvironments.

Absenteeism↗
PubMed1993

Methods for epidemiologic analyses of multiple exposures: a review and comparative study of maximum-likelihood, preliminary-testing, and empirical-Bayes regression.

Many epidemiologic investigations are designed to study the effects of multiple exposures. Most of these studies are analysed either by fitting a risk-regression model with all exposures forced in the model, or by using a preliminary-testing algorithm, such as stepwise regression, to produce a smaller model. Research indicates that hierarchical modelling methods can outperform these conventional approaches. I here review these methods and compare two hierarchical methods, empirical-Bayes regression and a variant I call 'semi-Bayes' regression, to full-model maximum likelihood and to model reduction by preliminary testing. I then present a simulation study of logistic-regression analysis of weak exposure effects to illustrate the type of accuracy gains one may expect from hierarchical methods. Finally, I compare the performance of the methods in a problem of predicting neonatal mortality rates. Based on the literature to date, I suggest that hierarchical methods should become part of the standard approaches to multiple-exposure studies.

Bayes Theorem↗
PubMed2000

Impact of environmental inequity on health outcome: where is the epidemiological evidence?

A significant amount of evidence reveals a presence of environmental inequity. Although there is a disproportionate distribution of waste treatment, storage and disposal facilities, and chemical and manufacturing plants in minority and low-income communities in the United States, little research has been devoted to show any associations based on analytic epidemiological methods. To date, attempts to quantify health disparities have included demographic data, race, sex, income, other socioeconomic factors, and broad symptomatic survey instruments. To study this, we examined the latest epidemiological evidence documenting the existence of adverse health impacts resulting from environmental inequity. We observed that the overwhelming majority of studies were descriptive in nature and lacked comparison populations. As a result, we believe that further research based on analytic epidemiological methods would further contribute to the determination of the cause-effect relationship between environmental exposure and health outcome.

Causality↗
PubMed2000

Statistical methods in epidemiology. VI. Correlation and regression: the same or different?

PURPOSE: The statistical terms 'correlation' and 'regression' are frequently mistaken for each other in the scientific literature. Why this is so is unclear. This paper discusses their differences/ similarities arguing that in most circumstances regression is the most appropriate technique to use, since regression incorporates a notion of dependency of one variable on another. METHOD: Pearson's correlation coefficient (r) is introduced as a method for estimating the degree of linear association between two normally distributed variables. The problem of least squares' regression (when y depends on x) is introduced by considering the best-fitting straight line between points on a scatter plot. RESULTS: Correlation, regression analysis and residual estimation are discussed by taking examples from the author's own teaching experiences. CONCLUSIONS: Correlation and regression share some similarities. However, regression is the better technique to use because with it comes a notion of dependency of one variable upon another. Regression model checking includes residual examination. The importance of plotting and examination of residuals cannot be overemphasized. Residual examination should become as much a part of a regression analysis as the estimation of the regression coefficients themselves.

Epidemiologic Methods↗
PubMed1989

Development of rapid epidemiologic assessment methods to evaluate health status and delivery of health services.

This paper describes the evolution of the concept of rapid epidemiologic assessment (REA) from a series of ideas to a defined area of epidemiologic research. Five broad areas of research are defined: small area survey and sampling methods, surveillance methods, screening and individual risk assessment, community indicators of risk or health status, and case-control methods for evaluation. REA techniques can provide health information more rapidly, simply and at less cost than the standard data collection methods and yet still yield reliable results. The use of these methods is described with examples from both a research programme designed to stimulate the development of REA methods and from other studies in the literature. The further development of REA techniques can lead to better decisions regarding the delivery and allocation of health services in both developing and industrialized countries.

Delivery of Health Care↗
PubMed1994

Gaps in epidemiologic research methods: design considerations for studies that use food-frequency questionnaires.

It is increasingly common for analytic epidemiology studies of diet and disease to select a semi-quantitative food-frequency questionnaire for dietary assessment. Reasons include its low cost and focus on usual intake. However, the components of variation in nutrient intake based on such methods are poorly understood, and it does not provide a quantitative estimate of nutrient intakes. Because it is unlikely that such methods will be improved substantially, studies using a food-frequency questionnaire should include a dietary standardization substudy. A substudy, conducted in a sample of study participants and aimed at collecting multiple days of diet recall or record, provides data for quantitative calibration of frequency-derived nutrient intake estimates and adjustment of risk estimates for measurement error. Attention should also be directed at other aspects of study design, such as study population selection to maximize dietary exposure contrasts, that can increase the informativeness of epidemiologic studies.

Diet↗
PubMed1994

Methods for epidemiological surveys of ethnic minority groups.

OBJECTIVE--Research into the health of minority ethnic groups is often restricted by methodological difficulties. These include the lack of accurate population denominators, the choice of an appropriate sampling frame, correctly assigning ethnic group, and biases in techniques used for sampling and investigation. This article reviews the available sources or mortality and morbidity data, and assesses their uses and limitations for research involving ethnic minority groups. Suitable sampling frames and review methods used to assign ethnicity are discussed. Sources of bias are high-lighted and methods used to overcome these biases are presented. CRITERIA FOR INCLUSION OF ARTICLES--Articles have been chosen which best illustrate the problems encountered and show how these problems can be addressed. CONCLUSIONS--The increased documentation of ethnic origin on routine data sources is welcomed, but attention must be paid to ensuring that congruent definitions in data collection are used. The worrying consequences of the Commission of European Communities directive, which describes the need for explicit consent to be obtained from subjects before data is used for anything other than its original purpose, are discussed.

Data Collection↗
PubMed1994

Network analytic methods for epidemiological risk assessment.

The authors measure the efficacy of three methods for predicting the time to infection for susceptible individuals in a population undergoing an HIV epidemic. The methods differ in whether they require detailed information of the contact network and whether they require knowledge of the initial source of infection. Efficacy is evaluated using simulations for 20 different contact patterns. Only the risk score that uses both kinds of information accounts for more than 15 per cent of individual variability. The efficacy of this score ranges from 10 per cent in very unstructured populations to 60 per cent for spatially localized contact networks. This improved performance may be explained by the larger fraction of the total variability not due to the disease dynamics. When all variables are dichotomized, the two poorer methods produce odds ratios between 1.4 and 2.3. The odds ratio for the risk score with full information ranges from 2.5 to 17. Risk assessment protocols and intervention programmes are encouraged to assess contact patterns and detect sources of infection.

Analysis of Variance↗
PubMed1999

Application of the capture-recapture method to epidemiological studies of alcohol related problems.

The capture-recapture method is used to enumerate members of populations for which a complete census is not possible. The use of this method to enumerate individuals with alcohol-related problems requires special considerations. This article comments on these considerations and addresses the strengths and weaknesses of this method for enumerating individuals with alcohol-related problems in a community.

Alcohol Drinking↗
PubMed1984

Epidemiological monitoring: methods for analysing routinely-collected data.

Morbidity and mortality statistics are routinely collected in many countries. These data may be arranged in a number of ways, for example, classified by area of residence, or occupation of the person concerned, or by the time-period during which the relevant event occurred. Judicious use of such data enables disease to be monitored and may draw attention to the adverse effects of harmful agents in the environment. This paper describes the different methods of analysing data for such purposes, giving examples of their application and discussing their relative merits. Particular reference is made to the data-collecting systems in England and Wales and to the statistical aspects of monitoring disease.

Communicable Diseases↗
PubMed1986

Interaction of genetics and epidemiology in the literature.

To evaluate the extent of interaction between genetics and epidemiology in studies reported in the literature, we reviewed all the "familial/genetic" papers published in a standard epidemiology journal (American Journal of Epidemiology, AJE) and all the "epidemiology" papers published in a standard human genetics journal (American Journal of Human Genetics, AJHG) between 1966 and 1984. A variety of medline subject headings were used in this search. Computerized listings of titles, subject headings, and abstracts were reviewed. It could be shown that familial/genetic papers constituted 4.3% of all papers published in AJE and epidemiology papers constituted 16.4% of papers published in AJHG. Over time, familial/genetic studies published in AJE increased both in number and in proportion of all papers, and more family studies are using complex statistical genetic techniques. On the other hand, epidemiology papers published in AJHG did not increase in number over time, and actually decreased in relation to all papers. These papers were mostly either descriptive (eg, defining frequencies of Mendelian traits in populations) or analytical (eg, defining risk factors for chromosomal abnormalities, and other reproductive outcomes). This analysis suggests that epidemiologic methods have been widely used in the genetic literature, and that genetic methods are gaining more access to the recent epidemiology literature. Because of increasing recognition of the role of genetic factors in disease, there is a growing need to incorporate both genetic and epidemiologic methods in etiologic studies of complex disorders.

Epidemiology↗
PubMed1989

Analysis of change over time.

A brief introduction is given to methods for analysis of epidemiological data where the exposure variable may change over time. The techniques discussed are related to both classical epidemiological methods for analysing the effect of a fixed, dichotomous exposure variable on a dichotomous response variable and to methods for analysis of life time data. Two examples are presented.

Adult↗
PubMed1993

Klebsiella pneumoniae infection on a rehabilitation unit: comparison of epidemiologic typing methods.

OBJECTIVE: To identify factors associated with an increased occurrence of Klebsiella pneumoniae isolation in urine cultures and infected wounds on a rehabilitation unit and to compare typing methods for K pneumoniae isolates. DESIGN: Retrospective review of laboratory reports and patient records with case-control study. Analysis of K pneumoniae isolates using capsular serotyping, enzyme electrophoretic typing, ribotyping, and DNA typing. SETTING: 48-bed rehabilitation unit in an 1,100-bed tertiary care teaching hospital in Winnipeg, Manitoba. RESULTS: In 1988, 20 (19%) of 106 patients admitted to the rehabilitation unit had K pneumoniae isolated from urine or wound, and in 1989 31 (28%) of 111 patients had Klebsiella isolated. Review of ward practices revealed appropriate written policies but evidence of failure in execution leading to multiple opportunities for transmission among patients. Substantial environmental contamination was not identified, although a common urine graduate may have contributed to some transmission. Individuals with K pneumoniae isolated had a significantly longer duration of stay. Many of these were spinal cord-injured patients and were maintained on intermittent catheterization. One outbreak strain was identified in epidemiologic typing. Other strains were generally identified in individuals with non-nosocomial acquisition of infection. Comparison of epidemiologic typing methods suggests ribotyping may be the optimal method for typing K pneumoniae strains. CONCLUSIONS: K pneumoniae was acquired frequently by spinal cord-injured patients with extended admissions, re-emphasizing the importance of both patients and staff following appropriate infection control practices on rehabilitation wards. Ribotyping was the optimal method for typing K pneumoniae isolates.

Adult↗
PubMed1989

Clinical economics education in the International Clinical Epidemiology Network. INCLEN Economics Faculty.

The application of rigorous epidemiologic methods to clinical questions has broadened the scope of research in epidemiology and enhanced the quality of clinical research. The International Clinical Epidemiology Network (INCLEN) has enabled physicians from developing countries to obtain training in epidemiologic methods and to provide leadership in clinical epidemiology in their home schools of medicine. The INCLEN program has recently incorporated another major theme of research training, clinical economics, which introduces research related to the effective use of limited resources. This article describes the rationale for the development of the INCLEN Clinical Economics program, outlines its organization and curriculum, and explores the challenges to its successful implementation.

Cost-Benefit Analysis↗
PubMed2000

Myocardial infarction and acute cholecystitis: an application of sequence symmetry analysis.

Using a statewide hospital discharge database and a novel epidemiology method, sequence symmetry analysis (Epidemiology. 1996;7:478-84), I examined the relative risk for hospital admission for acute cholecystitis after admission for myocardial infarction. In sequence symmetry analysis, the ratio of the number of subjects in a fixed population who experienced two events in a "causal" vs "noncausal" temporal sequence estimates the incidence rate ratio (IRR). Of 514 patients admitted for both myocardial infarction and acute cholecystitis during a 3-year window period, 295 were admitted for myocardial infarction first and 219 for acute cholecystitis first, yielding a null sequence-adjusted IRR of 1.45 [95% confidence interval (CI) = 1.28-1.64]. A similar analysis for a known relation (myocardial infarction-->congestive heart failure, N = 27,850) showed the expected association [adjusted IRR = 1.92 (95% CI = 1.88-1.95)], whereas an analysis for a relation hypothesized not to be strong (congestive heart failure-->acute cholecystitis, N = 775) showed only a small association [adjusted IRR = 1.16 (95% CI = 1.05-1.28)]. Subgroup analysis revealed time courses that supported each relation as causal. Hospitalization for myocardial infarction may increase the risk for subsequent hospitalization for acute cholecystitis.

Acute Disease↗