The J-shaped curve − conceptual and methodological challenge

Observational scientific evidence can usually be viewed as a form of measurement, and like any measurement, the measurement of a potential causal effect is subject to measurement error. In addition to statistical error, the measurement error of a scientific study subsumes problems that relate to study design, including subject selection and retention, information acquisition, and uncontrolled confounding and other sources of bias. Since nearly every study will have nearly every type of error, the real issue is to quantify the errors. The authors review the extent of the methodological problems in studies of the J-shaped curve and discuss the possibility that the J-shaped curve is an artefact created by reverse causality and residual confounding. Further the issue of possible effect modification of drinking pattern and type of alcohol is discussed.
The measurement error of imprecise categorization of alcohol intake information seems to have had little effect on the J-shaped alcohol-CHD-associations, nor has it affected the ability of these studies to show increasing mortality from a range of causes with increasing alcohol consumption. The problem of “sick quitters” has been adequately resolved by large studies using lifelong abstainers or infrequent drinkers as reference group. Too many studies lack information on drinking patterns with regard to regular, moderate consumption versus binge drinking. Stratified analyses by important risk factors for CHD have not significantly changed the J-shaped association observed in most epidemiologic studies.
The authors conclude that measurement errors like potential biases and residual confounding probably do not overcome the J-shaped alcohol-CDH-association observed in most epidemiologic studies, however, the existence of a J-shaped curve is challenged by some degree of uncertainty. Accordingly, the need for large-scale randomized trials to clarify the causal relation and to give greater insight into the health effects of population-wide alcohol consumption has been argued.
Source: Grønbæk, M., Ellison, R.C. and Skovenborg, E.(2020), “The J-shaped curve-conceptual and methodological challenges”, Drugs and Alcohol Today, Vol. 21 No. 1, pp. 70-83.