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Franz Porzsolt,1,2 Natália Galito Rocha,3 Alessandra C Toledo-Arruda,3 Tania G Thomaz,3,4 Cristiane Moraes,4 Thais R Bessa-Guerra,4 Mauricio Leão,5 Arn Migowski,6,7 André R Araujo da Silva,8 Christel Weiss2,9 1Health Care Research, Department of General and Visceral Surgery, University Hospital Ulm, Ulm, Germany; 2Institute of Clinical Economics (ICE) eV, Ulm, Germany; 3Department of Physiology and Pharmacology, Biomedical Institute, Universidade Federal Fluminense, Niterói, 4Cardiovascular Sciences, Universidade Federal Fluminense, Niterói, 5Institute of Nuclear Medicine, University Hospital Antonio Pedro, Niterói, 6National Cancer Institute (INCA), Rio de Janeiro, Brazil; 7National Institute of Cardiology (INC), Rio de Janeiro, Brazil; 8Department of Mother and Child, Faculty of Medicine, Universidade Federal Fluminense, Niterói, Rio de Janeiro, Brazil; 9Department of Medical Statistics, Medical Faculty Mannheim, University of Heidelberg, Mannheim, Germany Abstract: The discussion about the optimal design of clinical trials reflects the perspectives of theory-based scientists and practice-based clinicians. Scientists compare the theory with published results. They observe a continuum from explanatory to pragmatic trials. Clinicians compare the problem they want to solve by completing a clinical trial with the results they can read in the literature. They observe a mixture of what they want and what they get. None of them can solve the problem without the support of the other. Here, we summarize the results of discussions with scientists and clinicians. All participants were interested to understand and analyze the arguments of the other side. As a result of this process, we conclude that scientists tell what they see, a continuum from clear explanatory to clear pragmatic trials. Clinicians tell what they want to see, a clear explanatory trial to describe the expected effects under ideal study conditions and a clear pragmatic trial to describe the observed effects under real-world conditions. Following this discussion, the solution was not too difficult. When we accept what we see, we will not get what we want. If we discuss a necessary change of management, we will end up with the conclusion that two types of studies are necessary to demonstrate efficacy and effectiveness. Efficacy can be demonstrated in an explanatory, ie, a randomized controlled trial (RCT) completed under ideal study conditions. Effectiveness can be demonstrated in an observational, ie, a pragmatic controlled trial (PCT) completed under real-world conditions. It is impossible to design a trial which can detect efficacy and effectiveness simultaneously. The RCTs describe what we may expect in health care, while the PCTs describe what we really observe. Keywords: randomized controlled trial, pragmatic controlled trial, explanatory trial, pragmatic trial, ideal study conditions, real-world conditionsCorrigendumfor this paper has been published.