Relationship of dietary folate and vitamin B6 with coronary heart disease in women.
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Alcohol Drinking↗
Biomedical subjects
D Schaubel
Publications and source records attributed to D Schaubel.
Controlling confounding when studying large pharmacoepidemiologic databases: a case study of the two-stage sampling design.
Large drug databases have been the source of interesting developments for pharmacoepidemiologic research, because they provide relatively accurate drug exposure histories. An important limitation of these databases is the lack of information on potential confounders. One solution, developed more than a decade ago but not widely used, is "two-stage sampling," in which stage 1 is the collection of information on drug exposure and outcomes, and stage 2 is the collection of confounder data on a subset of the stage 1 sample. The balanced design, wherein an equal number of individuals is selected from each drug exposure/disease category, is usually the most efficient strategy by which to select the stage 2 sample. We illustrate the efficiency of the balanced design in two-stage sampling using data from a provincial health organization and a simulation. We also evaluate the relative importance of factors affecting the precision of the effect estimate of the exposure of interest.
Case-Control Studies↗
Two-stage sampling for etiologic studies. Sample size and power.
Preexisting computerized databases are potentially valuable sources of epidemiologic data. Since such databases are infrequently created specifically for etiologic research, data may be available for the exposure of interest and, through record linkage, for the endpoint of interest, but lacking for potential confounders. Because of the size of these databases, two-stage sampling is an efficient alternative to surveying the entire study population for confounder data. At stage 1, information on exposure and disease status is obtained for the entire study population. Confounder data are collected for probability-selected subsamples at stage 2. Logistic regression is performed on the stage 2 samples, with the parameter estimates and variances appropriately corrected to account for the stage 1 data. In this paper, the authors present methods for determining the required stage 2 sample size in the case of categorical exposure and confounding variables. Sample size tables, power curves, and a computer program have been produced to accommodate a binary exposure and a single binary confounder. With the increasing availability of preexisting yet incomplete databases, the potential for use of two-stage sampling will greatly increase in the future. This investigation provides a basis for estimating the number of participants to sample for the collection of confounder data at the second stage.
Case-Control Studies↗
Serum folate and risk of fatal coronary heart disease.
OBJECTIVE: To assess the relationship between serum folate level and the risk of fatal coronary heart disease (CHD) among men and women. DESIGN: Retrospective cohort study with serum folate levels measured from September 1970 to December 1972, with follow-up through 1985. SETTING: Participants in the Nutrition Canada Survey. PARTICIPANTS: A total of 5056 Canadian men and women aged 35 to 79 years with no history of self-reported CHD. MAIN OUTCOME MEASURE: Fifteen-year CHD mortality. RESULTS: A total of 165 CHD deaths were observed. We found a statistically significant association between serum folate level and risk of fatal CHD, with rate ratios for individuals in the lowest serum folate level category (<6.8 nmol/L [3 ng/mL]) compared with the highest category (>13.6 nmol/L [6 ng/mL]) of 1.69 (95% confidence interval, 1.10-2.61). CONCLUSIONS: These data indicate that low serum folate levels are associated with an increased risk of fatal CHD.
Adult↗
Risk of preschool asthma: incidence, hospitalization, recurrence, and readmission probability.
Asthma is one of the most common chronic illnesses in childhood. Increases in hospitalization rates have occurred in several countries. The cumulative risk of asthma requiring medical attention was 11.7% for males and 7.0% for females aged 0-4 in Manitoba, Canada, for the cohort of children born in 1984/1985. The cumulative risk of hospitalization for males was nearly twice that of females (2.1% vs. 1.1%). Disease onset was most likely at age 1 year. The risk of rehospitalization or return physician visit for asthma increased significantly with the number of prior hospitalizations and physician visits, respectively, which may reflect both the persistence of asthma and the difficulty of developing an effective disease management strategy.
Age of Onset↗
Neonatal characteristics as risk factors for preschool asthma.
Childhood asthma usually begins early in life. Neonatal characteristics are reportedly predictive of symptom onset. This investigation utilized data from a provincial health organization to evaluate the effect of several birth characteristics on asthma incidence and hospitalization for asthma during age 0-4. Using logistic regression, the odds ratios (OR) for the following variables indicate a significant (p < 0.05) association with physician-diagnosed preschool asthma: male gender (OR = 1.72), birthweight < 1500 g (OR = 2.11), prematurity (OR = 1.34), respiratory distress syndrome (RDS) in the presence (OR = 2.95) or absence (OR = 1.61) of bronchopulmonary dysplasia (BPD), and transient tachypnea of the newborn (TTN; OR = 1.36). Male gender (OR = 1.91), birthweight < 1500 g (OR = 2.56), RDS with and without BPD (OR = 3.35 and 2.50, respectively), TTN (OR = 2.08), and severe birth asphyxia (OR = 1.94) showed an important association with hospitalization due to asthma. Neonatal characteristics are important determinants for the risk of preschool asthma, even after mutual adjustment.
Asthma↗
Survival experience among elderly end-stage renal disease patients. A controlled comparison of transplantation and dialysis.
Renal transplantation is a relatively recent treatment option among the elderly with end-stage renal disease (ESRD). Since little is known regarding the clinical benefits of transplantation relative to dialysis in this age group, this study compares transplantation and dialysis among the elderly with respect to patient survival. Data utilized in this investigation were obtained from the Canadian Organ Replacement Register (CORR). The study population consisted of the 6400 patients aged 60 and over at registration, diagnosed between 1987 and 1993, for whom data on comorbid conditions were available. Survival probability, death rates, age-standardized mortality ratios (SMRs) and Cox regression analysis were employed to evaluate the survival experience among the transplant and dialysis groups. Transplant recipients were matched (by age, underlying diagnosis leading to ESRD, and number of comorbid conditions) to 2 randomly selected patients who did not undergo transplantation. Using Cox regression, the time-dependent hazard ratio for transplantation versus dialysis patients was estimated at 0.47 (P < 0.0001), indicating that even after adjusting for other known prognostic factors, elderly patients who received a transplant experienced significantly greater survival probability than those who remained on dialysis. When transplant patients were matched to randomly selected dialysis patients with the constraint that the corresponding dialysis patient have at least as much follow-up time as the transplant patient had waiting time, five-year survival rates were 81% and 51% for the transplant and dialysis groups, respectively (P < 0.0001). These results support the potential advantage of transplantation among the elderly, and may have important implications for renal care in this age group.
Age Factors↗
Inorganic components of drinking water and microalbuminuria.
Relatively little is known of the chronic effects attributable to the ingestion of inorganic components such as uranium and silicon. Although ingestion of large amounts of U can cause acute renal damage through a chemical effect, studies on humans have typically considered inhalation the route of exposure. We investigated the association between drinking water concentration levels of U and Si, and microalbuminuria, a sensitive biological indicator of renal dysfunction. Linear regression analysis revealed a statistically significant association between U cumulative exposure index and albumin per mmol creatinine (P = 0.03). No such significant relationship appeared for Si, although a positive trend was witnessed. Since normal but increasing levels of microalbuminuria were observed at U concentration levels below the Canadian Maximum Allowable Concentration (MAC), it is suggested that further study be undertaken.
Adolescent↗
New and prevalent patients with end-stage renal disease in Canada. A portrait of the year 2000.
The number of patients initiating treatment for end-stage renal disease (ESRD) has increased dramatically in Canada and other countries. To assist healthcare planners, the prevalence of ESRD in Canada has been projected to the year 2000 using a Markov modelling technique. Significant increases in ESRD are expected in Canada during the next decade, particularly among the elderly and diabetic populations: estimated increases in prevalence rates of ESRD between 1992 and the year 2000 were 78% and 154% for non diabetic and diabetic populations respectively. These expected increases did not differ significantly between the treatment groups, except among patients with diabetes, in whom projected increases in the prevalence of functioning transplant was smaller than for hemodialysis or peritoneal dialysis. Because the current Canadian prevalence rates are lower than those of some other countries, such as the United States and Japan, these expected trends in prevalence appear reasonable, and illustrate the growing healthcare needs of the ESRD population in Canada during the next decade.
Adolescent↗