CauseHealth offers a new ontological foundation for medicine, what we call Causal Dispositionalism (Mumford and Anjum 2011). From this perspective, better evidence would mean evidence of causation, understood as something tendential and intrinsic. Specifically, better evidence of causation would involve theoretical understanding of how and why an intervention brings about a certain effect. But we should try to develop this understanding to also include how various factors interact, for instance, what could counteract the effect, what could enforce it and what else is causally relevant for the outcome.
A causal dispositionalist would emphasise the epistemological value of qualitative evidence for deep causal knowledge, and also knowledge of the local context to which an intervention is added. Individual variations in effect are expected, since the intervention is interacting with different contexts. Therefore, for risk assessment, individual propensities and mechanistic understanding should be considered as at least equally important to statistical evidence, especially for rare effects.
To sum up, what counts as scientific evidence must be broadened, especially when it comes to causal evidence. Statistical evidence can indicate something; about which causes are linked to which effects. However, if we want to make decisions for individuals, we need to have what we call ‘deep causal knowledge’; of how the cause produces the effect and how it interacts with the individual patient. For this we need qualitative evidence, which can help us develop causal theory and understanding.