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Results for “Effect Modifier, Epidemiologic”

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PubMed1995

Maternal exposure to N-nitrosatable drugs as a risk factor for childhood brain tumours.

BACKGROUND: Animal models suggest that compounds containing a nitrosyl group (N-nitroso compounds (NNO)) can act as potent transplacental carcinogens. Many common drug formulations have the potential to undergo nitrosation in vivo. The association between maternal use of nitrosatable drugs during pregnancy and development of brain tumours in the offspring was examined in a SEER-based case-control study. METHODS: Maternal exposure to nitrosatable drugs during pregnancy was compared among 361 childhood brain tumour cases and 1083 matched controls recruited through random-digit dialing. RESULTS: There was no increase in risk observed for childhood brain tumours overall (OR = 1.15; 95% CI: 0.69-1.94) or for astrocytomas individually (OR = 1.16; 95% CI: 0.50-2.69). A slight elevation in risk was noted for medulloblastomas (OR = 1.47; 95% CI: 0.28-7.62) and 'other' tumours (OR = 1.27; 95% CI: 0.56-2.86), however, both estimates were based on small numbers. CONCLUSIONS: Our findings suggest that no increased risk of childhood brain tumours was associated with maternal exposure to nitrosatable drugs. The study results should be viewed with caution given the imprecision of the point estimates as well as the lack of data on specific timing and dosage of exposure and degree of nitrosatability of drugs taken.

Astrocytoma↗
PubMed1995

Use of experimental and quasi-experimental methods for data-based decisions in QI.

BACKGROUND: Decisions made by quality improvement (QI) teams, as reported in the literature, are usually based on nonexperimental methods for data collection. Pretest-posttest designs, in particular; are common in reports of QI teams' evaluations of changes or interventions. Yet in such designs the results are inherently confounded; it is impossible to rule out alternative explanations for any differences found. USING EXPERIMENTAL METHODS TO MAKE QI DECISIONS: As suggested by one study, QI teams can design and implement experimental interventions in relevant organizational processes. In an attempt to reduce the no-show rate for first appointments at a Residents Clinic at the Medical University of South Carolina (Charleston), the Youth Outpatient Improvement Team designed an experiment to test two possible modifications to the admission process. Those seeking services were randomly assigned to one of three groups (the control group or one of the experimental groups). Not only did results not support the team's hypothesis that one of the experimental procedures would produce a lower no-show rate, subjects in the experimental groups were less likely to enter treatment. Given these data, the decision was made to maintain current admission procedures. CONCLUSIONS: Since the quality of a decision is dependent on the quality of the data on which it is based, QI teams should consider experimental methods when planning data collection to evaluate their recommended interventions. When such methods are not feasible, quasi-experimental strategies can be used to strengthen the quality of nonexperimental data.

Adolescent↗
PubMed1995

Effect of maternal glucocorticoid exposure on risk of severe intraventricular hemorrhage in surfactant-treated preterm infants.

OBJECTIVE: To determine whether the reduced risk of severe intraventricular hemorrhage (SIVH) that follows antenatal maternal glucocorticoid (AMG) receipt is mediated by an AMG effect on blood pressure or improved respiratory function in infants who receive artificial surfactant as rescue therapy. DESIGN: Retrospective cohort study. SETTING: Two level III neonatal intensive care units, Boston, Mass. PARTICIPANTS: Two hundred twenty-five infants < or = 32 weeks of gestational age and < or = 1.7 kg birth weight, treated with surfactant. MAIN FINDINGS: SIVH occurred in 10% (10/102) of infants who were exposed to AMG, compared with 23% (25/111) of infants not exposed (odds ratio, 0.4; 95% confidence interval, 0.2 to 0.8). Hypotension and need for colloid or dopamine were associated with both SIVH and the absence of AMG exposure (p < or = 0.03). Logistic regression models of SIVH risk and AMG exposure, with adjustment for antenatal potential confounders, were altered by the addition of measures of hypotension. Most clinical measures of pulmonary function, both before and after surfactant receipt, were not associated with reduced risk of SIVH and did not appear to account for the increased risk of SIVH in babies not exposed to AMG. CONCLUSION: The reduced risk of SIVH in preterm newborn infants whose mothers received AMG was associated with normal blood pressures. The association between AMG and SIVH was not consistently enhanced by respiratory function improvement after surfactant therapy.

Cerebral Hemorrhage↗
PubMed1990

Loglinear models, sexual behavior and HIV: epidemiological implications of heterosexual transmission.

An analysis is presented of sexual behaviour data from a "random" sample (n = 780) of the adult population of England and Wales. Sex stratified frequency distributions of the reported number of sex partners/time were analysed for heterosexuals, demographic characteristics associated with the number of sex partners/time were identified, and epidemiological parameters (the basic reproductive rate of HIV and the doubling time of the epidemic) were calculated. These analyses suggest that the size of the group at risk for acquiring the virus by heterosexual transmission may be large and that the age of first sexual intercourse (for males and females) is decreasing in younger cohorts. Members of the potential heterosexual at-risk group may be identified by demographic variables such as marital status (males and females) and age (females only), but not by socioeconomic class. The epidemiological implications of our results for the heterosexual transmission of HIV are discussed.

Adolescent↗
PubMed1996

Interviewer effects on epidemiologic diagnoses of posttraumatic stress disorder.

In an epidemiologic study of 641 interviewed subjects in the Australian Vietnam Veterans Health Study, three diagnoses of Vietnam combat-related posttraumatic stress disorder (PTSD) were obtained: lifetime prevalence using a variant of the Diagnostic Interview Schedule and lifetime and current (1-month) PTSD prevalence using the Standardized Clincical Interview for the Diagnostic and Statistical Manual of Mental Disorders, Third Revision. Prevalence estimates using the Standardized Clinical Interview varied according to interviewer characteristics (female vs. male, clinician vs. nonclinician) but not for the Diagnostic Interview Schedule. The authors use a simple variant of logistic regression to distill estimates of two informative parameters characterizing interviewers' judgments: severity threshold (related to the individual interviewer's criterion of "caseness") and reliability (related to degree of classification error of the individual interviewers). Examination of these estimates shows that female clinicians adopted lower severity thresholds for diagnosis of PTSD than other interviewers and hence had higher prevalence estimates while being relatively reliable in their judgments. Examination also shows that nonclinician interviewers can perform at least as reliably as clinicians. The Diagnostic Interview Schedule measure of PTSD was not moderated by these interviewer aspects. This use of threshold and reliability parameters is offered for routine use in epidemiologic field studies to examine potential interviewer effects.

Australia↗
PubMed2003

Early exposure to allergen: is this the cat's meow, or are we barking up the wrong tree?

Several recent studies have suggested that exposure to cat and dog allergen in infancy is protective against the subsequent risk of allergic sensitization and asthma. The methodologic problems to be overcome in clinical research addressing these hypotheses are complex. Appreciation of these studies requires an assessment of the design and adequacy of variables measuring exposures, outcomes, and confounders. It includes understanding the role of effect modification. This article discusses some of the epidemiologic issues in interpreting these studies. Review of relevant epidemiology demonstrates that much research remains to be performed before these interesting hypotheses are proved or disproved.

Allergens↗
PubMed1999

Cancer mortality in Russia and Ukraine: validity, competing risks and cohort effects.

BACKGROUND: The dramatic increase in mortality in Russia and Ukraine in the late 1980s and 1990s has been due to increases in certain causes of death, particularly cardiovascular disease and accidents and violence. In contrast, there has been a slight fall in mortality from cancer. METHODS: This paper presents an analysis of trends and patterns in cancer mortality and examines four possible explanations for its recent fall: changes in data collection; cohort effects; competing mortality from other causes of death; and improvements in health care. RESULTS: All contribute to some extent to the observed changes, with each affecting predominantly different age groups. There is evidence of a significant underrecording of cancer deaths among the elderly especially in rural areas and of significant changes in coding practices in the early 1990s. Competing mortality from cardiovascular diseases and accidents can explain some reduction in male deaths from cancer in middle age. Birth cohort effects can explain some reduction among males after early middle age and among females at all ages. The impact of changes in health care are more difficult to identify with certainty but there is evidence of reduced deaths from childhood leukaemia. IMPLICATIONS: Recent changes in mortality in Russia are complex and their understanding will require a multidisciplinary approach embracing demography, epidemiology and health services research.

Adolescent↗
PubMed1995

Social desirability bias in dietary self-report may compromise the validity of dietary intake measures.

BACKGROUND: Self-report of dietary intake could be biased by social desirability or social approval thus affecting risk estimates in epidemiological studies. These constructs produce response set biases, which are evident when testing in domains characterized by easily recognizable correct or desirable responses. Given the social and psychological value ascribed to diet, assessment methodologies used most commonly in epidemiological studies are particularly vulnerable to these biases. METHODS: Social desirability and social approval biases were tested by comparing nutrient scores derived from multiple 24-hour diet recalls (24HR) on seven randomly assigned days with those from two 7-day diet recalls (7DDR) (similar in some respects to commonly used food frequency questionnaires), one administered at the beginning of the test period (pre) and one at the end (post). Statistical analysis included correlation and multiple linear regression. RESULTS: Cross-sectionally, no relationships between social approval score and the nutritional variables existed. Social desirability score was negatively correlated with most nutritional variables. In linear regression analysis, social desirability score produced a large downward bias in nutrient estimation in the 7DDR relative to the 24HR. For total energy, this bias equalled about 50 kcal/point on the social desirability scale or about 450 kcal over its interquartile range. The bias was approximately twice as large for women as for men and only about half as large in the post measures. Individuals having the highest 24HR-derived fat and total energy intake scores had the largest downward bias due to social desirability. CONCLUSIONS: We observed a large downward bias in reporting food intake related to social desirability score. These results are consistent with the theoretical constructs on which the hypothesis is based. The effect of social desirability bias is discussed in terms of its influence on epidemiological estimates of effect. Suggestions are made for future work aimed at improving dietary assessment methodologies and adjusting risk estimates for this bias.

Bias↗
PubMed2005

Bourdieu does environmental justice? Probing the linkages between population health and air pollution epidemiology.

The environmental justice literature faces a number of conceptual and methodological shortcomings. The purpose of this paper is to probe ways in which these shortcomings can be remedied via recent developments in related literatures: population health and air pollution epidemiology. More sophisticated treatment of social structure, particularly if based on Pierre Bourdieu's relational approach to forms of capital, can be combined with the methodological rigour and established biological pathways of air pollution epidemiology. The aim is to reformulate environmental justice research in order to make further meaningful contributions to the wider movement concerned with issues of social justice and equity in health research.

Air Pollution↗
PubMedDate not supplied

Basic occupational epidemiologic measures.

This chapter focuses on the "response" side of the exposure-response relationship and summarizes some of the measures of effect that are commonly used in occupational epidemiologic research. The author covers some basic statistical standardization procedures that are used to help compare these measures among groups that differ with respect to age or other factors.

Case-Control Studies↗
PubMedDate not supplied

The impact of age on cost-effectiveness ratios and its control in decision making.

Throughout Europe and in a number of other industrialized countries, the coming decades have been predicted to feature an increase in the proportion of patients who are elderly. This has led to considerable concern with respect to financing the health care system and has also increased the concerns about the efficiency of health care. Integrating ageing and efficiency issues, this paper examines the effects of age on the cost-effectiveness of medical interventions and its impact on decision making. First, at the clinical level, the relation between age and the cost-effectiveness of medical interventions is analysed. Second, at the population level, a framework is presented which allows researchers and decision makers to assess the impact of these effects on the decision-making process. It is shown that the allocation of health care resources at the macro-level is seriously impaired when age is ignored as a variable in cost-effectiveness analysis. Because clinical trials typically employ 'young' populations, when the data are extrapolated to the whole population the attractiveness of medical interventions in terms of cost-effectiveness may be considerably overestimated. Furthermore, the cost-effectiveness ratio may vary across countries or over time as a result of demographic or epidemiological variation. Economic evaluators should describe the impact of age, which should then be considered by decision makers to control for age effects.

Age Factors↗
PubMed1994

Completeness and accuracy of interview data from proxy respondents: demographic, medical, and life-style factors.

To evaluate the quality of exposure data provided by proxy respondents, we used a dual interview protocol in a case-control study of subarachnoid hemorrhage. All control subjects and their proxy respondents were interviewed (N = 283 control-proxy pairs), as were the cases who were able to provide their own information and their proxy respondents (N = 68 case-proxy pairs). The reliability of proxy-derived data was excellent for demographic and body habitus measures (kappa or intraclass correlation range = 0.86-0.99), and all aspects of cigarette smoking history (range = 0.79-0.93). Proxy reliability was somewhat lower for questions regarding medications and hormone preparations (range = 0.55-0.88), alcohol consumption (range = 0.52-0.82), and recreational physical activity (range = 0.55-0.67). Proxy reliability varied according to the relationship of the proxy to the index subject. Relative to the index subjects, proxy respondents tended to underreport the presence or level of exposure. For most exposures, odds ratios computed with proxy-derived data were similar in magnitude to odds ratios obtained with index subject data; important bias due to differential nonresponse or differential misclassification was suggested only for questions regarding hormone replacement therapy. Epidemiologic studies that rely on proxy respondents may require more subjects to offset the effect of nondifferential nonresponse and misclassification on the precision of effect estimates.

Adolescent↗
PubMed2002

Environmental epidemiology: basics and proof of cause-effect.

Bringing epidemiology and toxicology together to better understand cause and effect relationships requires attention to several interconnected problems: problems of commitment, complexity, and of communication. The most fundamental of these is commitment as it is reflected in the basic purpose of environmental epidemiology. The purpose of epidemiology is not to prove cause-effect relationships, and not only because scientific proof is elusive. The purpose of epidemiology is to acquire knowledge about the determinants and distributions of disease and to apply that knowledge to improve public health. A key problem, therefore, is how much and what kinds of evidence are sufficient to warrant public health (typically preventive) actions? The assessment of available evidence lays the foundation for the problem of complexity: relevant evidence arrives from toxicologic and epidemiological investigations, and reflects the acquisition of knowledge from many levels of scientific understanding: molecular, cellular, tissue, organ systems, complete organisms (man and mouse), relationships between individuals, and on to social and political processes that may impact human health. How to combine evidence from several levels of understanding will require the effective communication of current methodological practices. The practice of causal inference in contemporary environmental epidemiology, for example, relies upon three largely qualitative methods: systematic narrative reviews, criteria-based inference methods, and (increasingly) meta-analysis. These methods are described as they are currently used in practice and several key problems in that practice are highlighted including the relevance to public health practice of toxicological evidence.

Animals↗
PubMed1993

Validation studies using an alloyed gold standard.

A key assumption made when using a validation study to correct an estimate of relative risk for bias due to misclassification or measurement error is that the available measure, known to have error but nonetheless used routinely in the main study, is compared to a gold standard measured without error. In most epidemiologic applications, the putative gold standard is in fact measured with error. The effect of the violation of the assumption on the corrected estimate depends on the magnitudes of the errors in the two measures and on their correlation. In particular, when the errors are negatively correlated, independent, or weakly positively correlated, the corrected estimate will tend to overcorrect beyond the true value.

Bias↗
PubMed1990

Differential recall as a source of bias in epidemiologic research.

Differential recall between compared groups is discussed most often in the context of case-control studies. Cases, compared to controls, are suspected of providing a more complete report of their true exposure to an hypothesized risk factor, thereby biasing upwards the estimate of its effect. The present paper describes how differential recall can arise with any observational design in epidemiology; with any class of study variable, not only exposures; and may inflate or deflate the true value of the estimate of effect size. We list a variety of study designs and questionnaire tactics that aim to remedy these problems. The scope and magnitude of the bias created by differential recall and the efficacy of proposed remedies require further study.

Bias↗
PubMedDate not supplied

Confounding bias and effect modification in epidemiologic research.

The medical literature contains many studies of the clinical effectiveness of diagnostic tests and therapeutic interventions. Common problems in experimental design occur that influence the usefulness of original research. Confounding bias and effect modification are two important factors that affect whether clinicians ought to apply the findings of clinical research to the care of their patients. Investigators should minimize confounding biases in their work. Effect modification should be described so that readers can decide which of their patients will benefit from a particular study. This article uses a number of clinical examples to help the clinician and investigator understand the influences of bias and effect modification on clinical research.

Age Factors↗
PubMedDate not supplied

Cost-effectiveness of harm reduction in preventing hepatitis C among injection drug users.

OBJECTIVES: Hepatitis C (HCV) has emerged as a major epidemic among injection drug users (IDUs), with observed prevalence exceeding 70% in many American and European cities. This article explores the potential of syringe exchange programs (SEPs) to reduce HCV incidence and prevalence. DESIGN: A random-mixing epidemiological model is used to examine the potential impact of harm reduction interventions. METHODS: Steady-state analysis is used to scrutinize the impact of SEP on HCV incidence and prevalence and to examine the accuracy of short-term incidence analysis in predicting long-run program effects. RESULTS: SEP is predicted to have little impact on HCV incidence and prevalence within realistic populations of IDUs. CONCLUSIONS: Short-term incidence analysis substantially overstates SEP effectiveness and cost-effectiveness in preventing HCV. More comprehensive harm reduction models, coupled with referral of active IDUs to treatment, must complement syringe exchange to successfully contain highly infectious blood-borne diseases.

Blood-Borne Pathogens↗