Keynote 10 - One Size Fits None: Why an Idionomic Revolution Is Necessary for Our Field

Intervention science and practice faces a progressivity crisis: stagnant effect sizes, failed syndromal strategies, and a disconnect between science and practice. Despite decades of RCTs and proliferating protocols, personalization remains elusive, with practitioners lacking guidance for tailoring interventions to particular people. This talk shows that such stagnation stems from violations of ergodic assumptions in normative statistics. It is rooted in the dark history of biostatistics which falsely assumed for racist and antisemitic reasons that ensemble statistics are applicable to particular people (or couples or families or organizations). Almost always they are not. This plenary proposes idionomics: a dynamic, particularized science leveraging longitudinal data, AI, and evolutionary principles to model intraindividual processes first, then seeking nomothetic generalizations that enhance idiographic understanding. Empirical examples will illustrate how idionomics uncovers functional subgroups masked by aggregates, enabling a science of personalization. Idionomics revives functional analysis, aligns with precision medicine, empowers global practitioners beyond WEIRD biases and shifts attention from traditional evidence-based practice to practice-based evidence. If we are to create a more progressive science the future of our discipline demands a shift from ergodic illusions to a personalized and precision-based intervention science based on idionomic analysis.