Causal diagram depicting the relationship between body weight, pulmonary hypertension (PH), and mortality. Sub-clinical disease often results in weight loss, possibly due to loss of appetite or increased metabolic demands. Body weight (defined by BMI category) measured at time of PH diagnosis is affected by weight loss due to sub-clinical disease prior to disease diagnosis. Weight loss due to subclinical illness is also associated with increased mortality risk. Additionally, pulmonary hypertension (PH) is a collider; conditioning on PH will induce collider stratification bias.