A causal-web illustrating various levels of disease causality. Feedbacks from outcomes to preceding layers may also exist. For example, individuals or societies may modify their risk behavior based on health outcomes. The "driving force, pressure, state, exposure, effect" (DPSEE) model of Corvalan et al.  does consider the multiple layers of causality. These layers however focus the risk evolution process which is less suitable for multi-risk factor interaction within and between layers. More complete discussions of causality and multiple causes are provided by Yerushalmy and Palmer , Evans [57, 58], and Rothman and Greenland [26, 59].