It has been difficult to demonstrate that interprofessional education (IPE) and interprofessional collaboration (IPC) have positive effects on patient care quality, cost effectiveness of patient care, and healthcare provider satisfaction. Here we propose a detailed explanation for this difficulty based on an adjusted theory about cause and effect in the field of IPE and IPC by asking: 1) What are the critical weaknesses of the causal models predominantly used which link IPE with IPC, and IPE and IPC with final outcomes? 2) What would a more precise causal model look like? 3) Can the proposed novel model help us better understand the challenges of IPE and IPC outcome evaluations? In the format of a critical theoretical discussion, based on a critical appraisal of the literature, we first reason that a monocausal, IPE-biased view on IPC and IPC outcomes does not form a sufficient foundation for proper IPE and IPC outcome evaluations; rather, interprofessional organization (IPO) has to be considered an additional necessary cause for IPC; and factors outside of IPC additional causes for final outcomes. Second, we present an adjusted model representing the "multi-stage multi-causality" of patient, healthcare provider, and system outcomes. Third, we demonstrate the model's explanatory power by employing it to deduce why misuse of the modified Kirkpatrick classification as a causal model in IPE and IPC outcome evaluations might have led to inconclusive results in the past. We conclude by applying the derived theoretical clarification to formulate recommendations for enhancing future evaluations of IPE, IPO, and IPC. Our main recommendations: 1) Focus should be placed on a comprehensive evaluation of factual IPC as the fundamental metric and 2) A step-by-step approach should be used that separates the outcome evaluation of IPE from that of IPC in the overarching quest for proving the benefits of IPE, IPO and IPC for patients, healthcare providers, and health systems. With this critical discussion we hope to enable more effective evaluations of IPE, IPO and IPC in the future.