C. J. Wild

Prognosis after recovery from first acute myocardial infarction: Determinants of reinfarction and sudden death

Factors associated with total cardiac mortality, sudden cardiac death and reinfarction were studied in 325 male survivors aged younger than 60 years of age (mean 50) of a first myocardial infarction (MI). All patients had undergone exercise testing and cineangiocardiography 4 weeks after MI, 24% underwent coronary artery surgery and 30% received beta-blocking therapy. Patients were followed 1 to 6 years (mean 3.5). Total cardiac mortality was best predicted by the left ventricular (LV) ejection fraction (EF) and by a coronary prognostic index. In contrast, neither the severity of coronary arterial lesions measured with a scoring system nor the results of the exercise test gave significant prediction of mortality. Of the 2 major late sequelae of MI, reinfarction could not be predicted by any clinical or cineangiocardiographic variable. However, sudden death not associated with reinfarction was significantly more common (p less than 0.001) when EF was less than or equal to 40% than when it was greater than 40%. Comparison of patients with an EF less than or equal to 40% who did or did not die suddenly showed that LV dilation (high volumes at ventriculography) was an added risk factor, but the extent of coronary occlusions and stenoses was not. It is concluded that, at least for groups of patients treated with standard modern methods after MI, the main determinant of medium-term survival is the extent of LV damage. The state of the coronary arteries and the presence of ischemic myocardium during exercise are only of secondary importance for survival.

Semiparametric methods for response‐selective and missing data problems in regression

Suppose that data are generated according to the model f(y|x; θ) g(x), where y is a response and x are covariates. We derive and compare semiparametric likelihood and pseudolikelihood methods for estimating θ for situations in which units generated are not fully observed and in which it is impossible or undesirable to model the covariate distribution. The probability that a unit is fully observed may depend on y, and there may be a subset of covariates which is observed only for a subsample of individuals. Our key assumptions are that the probability that a unit has missing data depends only on which of a finite number of strata that (y, x) belongs to and that the stratum membership is observed for every unit. Applications include case–control studies in epidemiology, field reliability studies and broad classes of missing data and measurement error problems. Our results make fully efficient estimation of θ feasible, and they generalize and provide insight into a variety of methods that have been proposed for specific problems.

Risk factors for atopic dermatitis in New Zealand children at 3·5 years of age

Background  The prevalence of atopic dermatitis (AD) is increasing in Western societies. The hygiene hypothesis proposes that this is due to reduced exposure to environmental allergens and infections during early life.

Risk factors for obesity in 7-year-old European children: the Auckland Birthweight Collaborative Study

Objective: To identify risk factors associated with obesity in primary school children, with a particular focus on those which can be modified. To identify critical periods and growth patterns in the development of childhood obesity. Methods: 871 New Zealand European children were enrolled in a longitudinal study at birth and data were collected at birth, 1, 3.5 and 7 years of age. Data collected at 7 years included weight, height, bioelectrical impedance analysis (BIA), television viewing time and a 24 h body movement record (actigraphy). The outcome measure was percentage body fat (PBF), which was calculated at 3.5 and 7 years using BIA. Univariate and multiple regression analyses were carried out using PBF as a continuous variable. Results: Multivariable analysis found maternal overweight/obesity, maternal age, female gender, sedentary activity time and hours of television viewing to be independently associated with PBF at 7 years. Growth variables (birth weight, rapid weight gain in infancy, early (1–3.5 years) and middle childhood (3.5–7 years)) were also independently associated with adiposity at 7 years. There was a strong correlation between PBF at 3.5 years and PBF at 7 years. Conclusions: Many primary school aged children start on the trajectory of obesity in the preschool years, which suggests interventions need to start early. Maternal overweight/obesity, television watching, sedentary activity time and rapid weight gain in infancy, early and middle childhood are risk factors for childhood obesity, and are all potentially modifiable.

Maternal nutritional risk factors for small for gestational age babies in a developed country: a case-control study

Aims: To assess the effect of maternal diet during pregnancy on the risk of delivering a baby who is small for gestational age (SGA). Methods: Case-control study of 844 cases (SGA) and 870 controls (appropriate size for gestational age (AGA)). Only term (37+ completed weeks of gestation) infants were included. Retrospective food frequency questionnaires were completed at birth on the diet at the time of conception and in the last month of pregnancy. Results: At the time of conception, mothers of AGA infants ate significantly more servings of carbohydrate rich food and fruit, and were more likely to have taken folate and vitamin supplements than mothers of SGA infants. There was some evidence that mothers of AGA infants also ate more servings of dairy products, meat, and fish (0.05 < p < 0.1). However, after adjustment for maternal ethnicity, smoking, height, weight, hypertension, and occupation, fish intake (p  =  0.04), carbohydrate-rich foods (p  =  0.04), and folate supplementation (p  =  0.02) were associated with a reduced risk of SGA. In the last month of pregnancy, only iron supplementation was associated with a reduced risk of SGA (p  =  0.05) after adjustment for potential confounders. Conclusions: This study suggests that small variations in maternal diets within the normal range during pregnancy in developed countries are associated with differences in birth weight.

Microalbuminuria in a Middle-Aged Workforce: Effect of hyperglycemia and ethnicity

OBJECTIVE To determine the prevalence of microalbuminuria in a mixed, thnic population and to find the extent that ethnic variation in microalbuminuria can be explained by abnormal glucose metabolism, obesity, hypertension, hypertriglyceridemia, and life-style factors. RESEARCH DESIGN AND METHODS Urinary albumin concentrations were measured in 5467 middle-aged Maori, Pacific Islander, and European workers who participated in a health-screening survey of 46 New Zealand companies. Participants provided a first-voided, morning urine sample; had a 75-g oral glucose tolerance test; had weight, height, and blood pressure measured; and completed a self-administered questionnaire about past medical history and sociodemographic status. RESULTS A significantly higher prevalence of microalbuminuria was found in individuals with new cases of diabetes mellitus (24.1%), in cases of diabetes mellitus previously diagnosed (20.6%), and in those with impaired glucose tolerance (16.1%) compared with nondiabetic individuals (4.0%). Moreover, in the general population, a piecewise linear relationship was detected between albuminuria and plasma glucose with significant changes of slope corresponding with 2 h plasma glucose concentrations (95% confidence interval) of 6.7 (6.4–7.0) and 9.2 (8.6–9.8) mM, respectively. After adjusting for sex, obesity, hypertension, hypertriglyceridemia, cigarette smoking, and heavy alcohol consumption in a multivariate model, glycemia was the most significant determinant of urinary albumin concentrations in all three ethnic groups. However, blood glucose concentrations did not completely explain the higher relative risk (95% confidence interval) of microalbuminuria in Maori (5.97; 4.48–7.78) and Pacific Islander (5.33; 4.13–6.87) workers compared with European workers. CONCLUSIONS Of the variables investigated, hyperglycemia was the most important factor explaining the high prevalence of microalbuminuria in Maori and Pacific Islander workers compared with the European workers. However, only 14.9% of the variation in urinary albumin concentrations was found in our multivariate model, and we have speculated on the contribution of other factors such as diet and coexisting renal diseases.

Transformations and R 2

Abstract The coefficient of determination, R 2, is widely used to compare the fit of competing regression models in spite of repeated warnings about the potential dangers. The use of R 2 is particularly inappropriate if the models are obtained by different transformations of the response scale. In this article we give a real example where two models are identical for all practical purposes and yet have very different values of R 2 calculated on the transformed scales.

Fitting Logistic Regression Models in Stratified Case-Control Studies

SUMMARY Methods are developed for fitting logistic models to data in which cases and/or controls are sampled from the available cases and controls within population strata. Particular attention is paid to models in which stratum differences are modelled as well as the effects of the different risk factors experienced by individuals within strata. Maximum likelihood estimation is developed for discrete explanatory variables and is compared with the method of Fears and Brown (1986, Biometrics 42, 955-960) and Breslow and Cain (1988, Biometrika 75, 11-20), in which the prospective logistic model is fitted with a fixed offset. An example is explored in which maximum likelihood estimation proves to be substantially more efficient than the Fears-Brown method and the modelling of the stratum effects leads to much more efficient estimates of regression coefficients for the remaining variables.

Smoking, nicotine and tar and risk of small for gestational age babies

Aims: To assess the effect of maternal smoking and environmental tobacco smoke (ETS) on risk of small for gestational age infants (SGA). Methods: Case‐control study of 844 cases and 870 controls. Results: Maternal smoking in pregnancy was associated with an increased risk of SGA (adjusted odds ratio (OR) = 2.41; 95% confidence interval (CI) = 1.78, 3.28). We could not detect an increased risk of SGA with paternal smoking, or with other household smokers when the mother was a non‐smoker, but did find an increased risk with exposure to ETS in the workplace or while socializing. Infants of mothers who ceased smoking during pregnancy were not at increased risk of SGA, but those who decreased but did not stop remained at risk of SGA. There was no evidence that the concentration of nicotine and tar in the cigarettes influenced the risk of SGA.

Maximum likelihood for generalised case-control studies

Abstract Suppose that we have a population of units with values ( x , y ) , where x is a vector of covariates and y is a response variable, generated according to the model f( y | x ; θ )g( x ) . Both x and y can be multivariate and any elements of x and y can be either discrete or continuous. The first term, f( y | x ; θ ) , is some regression model linking response-variable behaviour to that of the covariates and we are interested in fitting this model. We discuss semiparametric maximum-likelihood estimation of θ for a class of study designs and data structures in which some units are not fully observed and in which it is impossible or undesirable to model the covariate distribution, g( x ) , which is typically of little interest in its own right. The key feature of the designs is that the probability that a unit is fully observed can depend on the value of the response, y . Applications include a number of useful generalisations of the basic case-control design and a broad class of missing data and measurement-error problems.