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Biomedical subjects

Jay S Kaufman

Publications and source records attributed to Jay S Kaufman.

At least 19 recordsLinked to original sources
PubMed2005

Improved estimation of controlled direct effects in the presence of unmeasured confounding of intermediate variables.

Adjusting for a causal intermediate is a common analytic strategy for estimating an average causal direct effect (ACDE). The ACDE is the component of the total exposure effect that is not relayed through the specified intermediate. Even if the total effect is unconfounded, the usual ACDE estimate may be biased when an unmeasured variable affects the intermediate and outcome variables. Using linear programming optimization to compute non-parametric bounds, we develop new ACDE estimators for binary measured variables in this causal structure, and use root mean square confounding bias (RMSB) to compare their performance with the usual stratified estimator in simulated distributions of target populations comprised of the 64 possible potential response types as well as distributions of target populations restricted to subsets of 18 or 12 potential response types defined by monotonicity or no-interactions assumptions of unit-level causal effects. We also consider target population distributions conditioned on fixed outcome risk among the unexposed, or fixed true ACDE in one stratum of the intermediate. Results show that a midpoint estimator constructed from the optimization bounds has consistently lower RMSB than the usual stratified estimator both unconditionally and conditioned on any risk in the unexposed. When conditioning on true ACDE, this midpoint estimator performs more poorly only when conditioned on an extreme true ACDE in one stratum of the intermediate, yet outperforms the stratified estimator in the other stratum when interaction is permitted. An alternate 'limit-modified crude' estimator can never perform less favourably than the stratified estimator, and often has lower RMSB.

Bias↗
PubMed2005

Accessing a new medication in Germany: a novel approach to assess a health insurance-related barrier.

PURPOSE: Knowledge of the existence, position, and magnitude of barriers to equitable healthcare is an important consideration in shaping healthcare policies. METHODS: The authors developed a novel three-dimensional person-time-related hurdle model and followed a cohort of 7358 statutorily (SHI) and 457 privately health insured (PHI) patients with migraine headaches at 377 primary-care practices (MediPlus, IMS Health) in the second to fourth year of the HealthCare Structural Reform Act in Germany. RESULTS: For SHI compared with PHI migraine patients, there was a hurdle to receiving sumatriptan at all (2.4-fold lower hazard, 95% confidence interval, 1.8-3.2). Among patients who received sumatriptan, frequency and intensity of use differed only minimally between SHI and PHI patients. CONCLUSIONS: These findings have implications for healthcare researchers and healthcare policies. The framework extends traditional hurdle models and can serve as a model for quantifying barriers to receipt of services under different funding policies.

Adolescent↗
PubMed2005

Evaluating the evidence for models of life course socioeconomic factors and cardiovascular outcomes: a systematic review.

BACKGROUND: A relatively consistent body of research supports an inverse graded relationship between socioeconomic status (SES) and cardiovascular disease (CVD). More recently, researchers have proposed various life course SES hypotheses, which posit that the combination, accumulation, and/or interactions of different environments and experiences throughout life can affect adult risk of CVD. Different life course designs have been utilized to examine the impact of SES throughout the life course. This systematic review describes the four most common life course hypotheses, categorizes the studies that have examined the associations between life course SES and CVD according to their life course design, discusses the strengths and weaknesses of the different designs, and summarizes the studies' findings. METHODS: This research reviewed 49 observational studies in the biomedical literature that included socioeconomic measures at a time other than adulthood as independent variables, and assessed subclinical CHD, incident CVD morbidity and/or mortality, and/or the prevalence of traditional CVD risk factors as their outcomes. Studies were categorized into four groups based upon life course design and analytic approach. The study authors' conclusions and statistical tests were considered in summarizing study results. RESULTS: Study results suggest that low SES throughout the life course modestly impacts CVD risk factors and CVD risk. Specifically, studies reviewed provided moderate support for the role of low early-life SES and elevated levels of CVD risk factors and CVD morbidity and mortality, little support for a unique influence of social mobility on CVD, and consistent support for the detrimental impact of the accumulation of negative SES experiences/conditions across the life course on CVD risk. CONCLUSIONS: While the basic life course SES study designs have various methodologic and conceptual limitations, they provide an important approach from which to examine the influence of social factors on CVD development. Some limitations may be addressed through the analysis of study cohorts followed from childhood, the evaluation of CVD risk factors in early and middle adulthood, and the use of multiple SES measures and multiple life course analysis approaches in each life course study.

Cardiovascular Diseases↗
PubMed2005

Mediation and modification of the association between hopelessness, hostility, and progression of carotid atherosclerosis.

Hopelessness and hostility are linked to progression of carotid atherosclerosis (PCA). The purpose of this study was to replicate such relations and to evaluate the role of biological pathways involving hyperactivation of the sympathetic nervous system (SNS) and the hypothalamic-pituitary-adrenocortical (HPA) axis. PCA was evaluated by 4-year change in three ultrasound measures of intima-media thickness (IMT) in 1027 men aged 42-60 years at baseline. Effect modification and mediation of relationships between psychosocial factors and PCA were examined for the measures systolic blood pressure (SBP), fibrinogen, and waist-to-hip ratio (WHR), levels of which are indicative of activity along these pathways. Hopelessness and hostility were associated with PCA. Fibrinogen mediated to a moderate extent the association between hopelessness and PCA. SBP significantly modified the relation between hostility and PCA in participants of moderate hostility. The above biological pathways are implicated in the mechanisms connecting hopelessness, hostility, and PCA.

Adult↗
PubMed2005

The epidemiology of threatened preterm labor: a prospective cohort study.

OBJECTIVE: The purpose of this study was to describe the occurrence, timing, and outcomes of hospital-based diagnoses of preterm labor. STUDY DESIGN: Administrative records identified hospital admissions for preterm labor among 2534 women in an ongoing cohort study. Factors that were considered risks for prematurity were examined by logistic regression for an association with any preterm labor diagnosis, a preterm labor diagnosis <33 weeks of gestation, or > or =33 weeks of gestation. RESULTS: Of 234 women (9%) who experienced hospitalization for preterm labor, 90 women (38%) were delivered in the first episode. Previous preterm birth consistently was associated with a diagnosis of preterm labor. Reporting a sexually transmitted infection (odds ratio, 1.8; 95% CI, 1.1-3.0) or bacterial vaginosis (odds ratio, 2.6; 95% CI, 1.7-4.1) early in pregnancy was associated with hospitalization for preterm labor between 24 and 32 weeks of gestation. CONCLUSION: The incidence of first-time hospitalization for preterm labor was 9%, with most episodes not resulting in preterm birth. Previous preterm birth was associated therefore with a preterm labor diagnosis.

Adolescent↗
PubMed2005

Urbanization and breast cancer incidence in North Carolina, 1995-1999.

PURPOSE: Breast cancer incidence rates are reported to be higher in urban compared with rural areas in the United States. We investigated the relationship between urbanization and breast cancer in North Carolina (1995-1999), and considered hospital characteristics as an explanation. METHODS: We calculated age-adjusted in situ and invasive female breast cancer incidence rates stratified by race, urbanization (Urban Influence Codes), and the presence of a hospital with a cancer registry and cancer program approval in a county. RESULTS: For white women, incidence rate ratios (IRRs) comparing the most urban with the most rural counties were 1.60 for in situ and 1.18 for invasive cancer. For non-white women, IRRs were 1.27 and 0.99, respectively. IRRs for incidence in registry hospital counties versus those without were all > 1.00 and differences were greater for in situ cancer than invasive. For most strata, urban excesses were attenuated when further stratified by registry hospital status. CONCLUSIONS: For most strata, we observed excess incidence in urban counties, but it appeared to be explained through the urban preponderance of registry hospitals. Counties with these hospitals may have higher incidence because of increased detection. Area hospital characteristics should be considered when evaluating geographic patterns of breast cancer incidence.

Adult↗
PubMed2005

Maternal urine albumin excretion and pregnancy outcome.

BACKGROUND: Vascular dysfunction has been hypothesized as a causal pathway for preeclampsia, impaired fetal growth, and early parturition. The relationship between increased urine albumin excretion (albuminuria), a marker of endothelial dysfunction, and preterm birth has not been fully evaluated. METHODS: We conducted a nested case-control study of 404 pregnancies from 1998 to 2000 within the Pregnancy, Infection and Nutrition cohort. Cases consisting of live births delivered before 37 weeks of gestation (preterm birth, n = 111) were compared with term births from the same cohort (n = 293). Albumin-creatinine ratio (in milligrams per gram) was measured in urine collected around 27 weeks of gestation. We compared risks for preterm birth in mothers with albuminuria with albumin levels of 3 to 20 mg/g and greater than 20 mg/g relative to those with albumin levels less than 3 mg/g by using logistic regression. RESULTS: Median albuminuria was albumin level of 2.7 and 4.3 mg/g for term and preterm births, respectively. Albuminuria was strongly associated with preterm birth in a dose-response fashion, with adjusted odds ratios of 1.9 (95% confidence interval, 1.1 to 3.1) and 4.7 (95% confidence interval, 1.7 to 12.6) for albuminuria with albumin of 3 to 20 mg/g and greater than 20 mg/g, respectively. The association was present for both spontaneous and medically induced preterm births, but the effect was decreased and the dose-response relationship was eliminated by excluding high-risk groups and those with pregnancy complications. CONCLUSION: Low levels of albuminuria are associated with preterm birth. The mechanism underlying this association warrants additional exploration.

Adult↗
PubMed2005

Bounding causal effects under uncontrolled confounding using counterfactuals.

Common sensitivity analysis methods for unmeasured confounders provide a corrected point estimate of causal effect for each specified set of unknown parameter values. This article reviews alternative methods for generating deterministic nonparametric bounds on the magnitude of the causal effect using linear programming methods and potential outcomes models. The bounds are generated using only the observed table. We then demonstrate how these bound widths may be reduced through assumptions regarding the potential outcomes under various exposure regimens. We illustrate this linear programming approach using data from the Cooperative Cardiovascular Project. These bounds on causal effect under uncontrolled confounding complement standard sensitivity analyses by providing a range within which the causal effect must lie given the validity of the assumptions.

Adrenergic beta-Antagonists↗
PubMed2004

A further critique of the analytic strategy of adjusting for covariates to identify biologic mediation.

BACKGROUND: Epidemiologic research is often devoted to etiologic investigation, and so techniques that may facilitate mechanistic inferences are attractive. Some of these techniques rely on rigid and/or unrealistic assumptions, making the biologic inferences tenuous. The methodology investigated here is effect decomposition: the contrast between effect measures estimated with and without adjustment for one or more variables hypothesized to lie on the pathway through which the exposure exerts its effect. This contrast is typically used to distinguish the exposure's indirect effect, through the specified intermediate variables, from its direct effect, transmitted via pathways that do not involve the specified intermediates. METHODS: We apply a causal framework based on latent potential response types to describe the limitations inherent in effect decomposition analysis. For simplicity, we assume three measured binary variables with monotonic effects and randomized exposure, and use difference contrasts as measures of causal effect. Previous authors showed that confounding between intermediate and the outcome threatens the validity of the decomposition strategy, even if exposure is randomized. We define exchangeability conditions for absence of confounding of causal effects of exposure and intermediate, and generate two example populations in which the no-confounding conditions are satisfied. In one population we impose an additional prohibition against unit-level interaction (synergism). We evaluate the performance of the decomposition strategy against true values of the causal effects, as defined by the proportions of latent potential response types in the two populations. RESULTS: We demonstrate that even when there is no confounding, partition of the total effect into direct and indirect effects is not reliably valid. Decomposition is valid only with the additional restriction that the population contain no units in which exposure and intermediate interact to cause the outcome. This restriction implies homogeneity of causal effects across strata of the intermediate. CONCLUSIONS: Reliable effect decomposition requires not only absence of confounding, but also absence of unit-level interaction and use of linear contrasts as measures of causal effect. Epidemiologists should be wary of etiologic inference based on adjusting for intermediates, especially when using ratio effect measures or when absence of interacting potential response types cannot be confidently asserted.

Journal Article↗
PubMed2004

Proximity of supermarkets is positively associated with diet quality index for pregnancy.

OBJECTIVES: To investigate the association between distance to the closest supermarket and a composite measure of diet, the diet quality index for pregnancy (DQI-P) was constructed. METHODS: Data from the Pregnancy, Infection and Nutrition (PIN) cohort, a prospective study of determinants of preterm birth, were analyzed. Food frequency questionnaires were used to construct DQI-P which includes: servings of grains, vegetables, fruits, folate, iron and calcium intake, percentage of calories from fat, and meal pattern score. Street address of residence, supermarkets, grocery and convenience stores were geocoded. Participants with complete food frequency and address data were included (n = 918). Multinomial logistic regression was used to estimate the conditional association of food outlets on diet quality, controlling for confounders and using a robust variance estimator to account for clustering of neighborhood characteristics. RESULTS: Women living greater than 4 miles from a supermarket were more than twice the odds (adjusted odds ratio = 2.16; 95% confidence interval = 1.2, 4.0) of falling into the lowest compared to highest DQI-P tertile compared to women living within 2 miles of a supermarket, after controlling for individual characteristics, other food retail outlets. CONCLUSION: These findings suggest that proximity of food retail outlets influences the diet quality of pregnant women.

Adolescent↗
PubMed2004

Quantifying delay in access to new medical treatment: an application of risk advancement period methodology.

BACKGROUND: We present a novel application of the concept of risk or rate advancement to compute the extent of delay in adoption of an effective new drug in 2 German health insurance systems. METHODS: We identified individuals with migraines, age 18 to 65 years, in 371 primary care practices in Germany in 1994 (MediPlus, IMS Health database). These included 8173 persons covered under the statutory health insurance system and 503 persons covered by private health insurance. We derived risk and population risk advancement periods for sumatriptan compared with nonserotoninergic acute migraine therapy using multiplicative risk regression and generalized estimating equations, adjusted for patient, physician, and practice cofactors. RESULTS: For patients at the mean age of the cohort, 43 years of age, sumatriptan was prescribed 1.2 (95% confidence interval [CI] = 0.3-2.0) years later among those in the statutory health insurance system compared with those who had private insurance. The lag increased by 0.6 (-0.1 to 1.3) years for every 10 years of patient age. In the age-mix of our sample, access to the health benefits of sumatriptan therapy lagged nearly 1.5 years behind in the statutory health insurance system and for Germany as a whole. CONCLUSIONS: Migraine patients' access to sumatriptan therapy lagged substantially in the statutory health insurance system and in the country as a whole. Risk advancement periods provide a useful methodology for communicating major healthcare issues in a meaningful way to society and policymakers.

Adult↗
PubMed2004

The disparity in access to new medication by type of health insurance: lessons from Germany.

BACKGROUND: Drug provision within the German statutory health insurance system has undergone several reforms, including the introduction of drug macrobudgets in 1993. OBJECTIVE: The objective of this study was to investigate the extent to which statutorily (SHI) and fully privately (PHI) health-insured patients were provided with new medication recommended by professional bodies in an equitable fashion using the example of migraine patients. RESEARCH DESIGN: We conducted a retrospective cohort study. SETTING: A total of 367 primary-care practices (MediPlus, IMS Health) in Germany in the second year of the HealthCare Structural Reform Act were studied. SUBJECTS: Subjected consisted of 7703 SHI and 470 PHI migraineurs (International Classification of Diseases, 10th edition G43) aged 18 to 65 years at their first migraine prescription visit in 1994. OUTCOME MEASURE: We compared prescription of oral or subcutaneous serotonin 5HT1B/1D receptor agonist sumatriptan with nonserotoninergic migraine therapy. RESULTS: In multiplicative risk regression with variance estimation accounting for clustering of patients within practices, PHI patients were 2.3 times (95% confidence interval [CI], 1.6-3.3) more likely to receive sumatriptan than their SHI counterparts at the mean age of the cohorts (43 years) adjusted for incident versus prevalent migraine treatment, the gender of the patient, the age, gender, and primary care specialist group of the physician, and the type and the community size class of the practice. This disparity widened by 38% (95% CI, 1-88%) every 10 years of patient age. CONCLUSION: Even though virtually everyone in Germany has health insurance and drug coverage, use of new and recommended migraine medicines was less common among those with SHI compared with their privately insured counterparts. Systematic studies of access to health care recommended by professional bodies will be critically important to ensure delivery of high-quality health care for all patients.

Adolescent↗
PubMed2004

A study in contrasts: measures of racial disparity in rates of sexually transmitted disease.

BACKGROUND: Although relative measures are commonly used to express health disparities, absolute measures could have more value in public health decision-making. GOAL: The goal of this study was to examine how associations between county-level variables and black-white racial disparity in gonorrhea rates varied by the measure of disparity used. STUDY DESIGN: We studied correlations of 10 population-level variables with the incidence rate difference (RD) and incidence rate ratio (RR) of gonorrhea in North Carolina (NC) counties. RESULTS: Nine of the 10 variables correlated more strongly with the RD than the RR. The RD was highly correlated with incidence rates of gonorrhea among blacks (r >0.99). CONCLUSION: Several county-level variables were correlated with absolute, but not with relative, racial disparity in gonorrhea in NC. Disease rates were so disparate that the RD essentially reflected rates in the black population. The RD should be preferentially used in planning and evaluating interventions aimed at eliminating racial disparities in gonorrhea in NC.

Adolescent↗
PubMed2004

Family socioeconomic status and self-reported sexually transmitted diseases among black and white american adolescents.

OBJECTIVE: The objective of this study was to assess associations between socioeconomic status (SES) and adolescent sexually transmitted diseases (STDs) stratified by race and gender. STUDY: In cross-sectional analyses of the National Longitudinal Study of Adolescent Health Wave One (1995), unadjusted and adjusted associations between 4 family SES indicators and STD reports for black and white 7th through 12th graders were examined. RESULTS: Lower maternal education and nonprofessional maternal occupations were associated with higher STD reports in all groups except white females. Generally, STD reports were higher for adolescents not living in 2-parent homes, and lower income was only associated for black males. CONCLUSION: Overall, SES is only a weak to moderate marker for adolescent STD risks. The relationship of SES and STDs varies by the SES measure used and differs across race-gender groups. Other individual factors such as risk behaviors or community factors such as income inequality could play a more critical role for adolescent STDs than family SES.

Adolescent↗