RESUMO
The key analytical challenge presented by longitudinal data is that observations from one individual tend to be correlated. Although longitudinal data commonly occur in medicine and public health, the issue of correlation is sometimes ignored or avoided in the analysis. If longitudinal data are modelled using regression techniques that ignore correlation, biased estimates of regression parameter variances can occur. This bias can lead to invalid inferences regarding measures of effect such as odds ratios (OR) or risk ratios (RR). Using the example of a childhood health intervention in Brazil, we illustrate how ignoring correlation leads to incorrect conclusions about the effectiveness of the intervention.
Assuntos
Modelos Logísticos , Estudos Longitudinais , Avaliação de Resultados em Cuidados de Saúde/métodos , Fatores Etários , Brasil , Creches , Pré-Escolar , Humanos , Lactente , Modelos Biológicos , Avaliação Nutricional , Razão de Chances , Fatores de Tempo , Síndrome de Emaciação/epidemiologia , Síndrome de Emaciação/prevenção & controleRESUMO
This study provides a detailed description of passive smoking by 433 infants (mean age 18 days) enrolled from a representative population of healthy neonates in central North Carolina during 1986 and 1987. Sixty-four percent (276) lived in households with smokers or had contact with nonhousehold smokers. During the week before data collection, two thirds (184) of these 276 infants reportedly had tobacco smoke produced in their presence. Seventy-five percent of smoking mothers smoked near their infants. The amount smoked by the mother near the infant correlated with the amount smoked near the infant by nonmaternal smokers. Cotinine, an indicator of smoke absorption, was found in the urine of 60% (258) of all study infants. The amount smoked in the infant's presence, as well as the amount smoked farther away from the infant, especially by the mother, were the most significant correlates of the urine cotinine concentration. The results of this study suggest that efforts to reduce passive smoking in young infants should emphasize the importance of the mother's smoking behavior, smoke produced anywhere in the home, and household social influences on smoking behavior near the infant.