Hello all,Birger, Ken, Lubomir, Ranjan, Luke, Chuck and others who have contributed,
This issue of "evidence-based" practice, as discussed by Lubomir and Birger, evidence-based practice, as per Ken and Chuck , and Evidence-based Design, or EBD, has issues as its root of value assumptions and knowledge construction.
(Caveat on this post - I have just a short moment to post and references are missing - if you would like a more expanded version with full  references please let me know; also if I have missed anyone's post, apologies).  
I have been studying this question for some time ( since 1994) and questions arise about the underlying values used in EBD in particular.Evidence-based design research is not the same as EBD. EBD has its roots, as Lubomir and Birger noted, in engineering and architecture, but more recently in interior design specifically where EBD is touted as the only "evidence-based" design option available. However, this version is rooted in positivist knowledge construction, and lately the trouble is it is being "sold" to professionals as the only was to do good design. This is currently a real problem in interior design, as those trying to show how knowledge in constructed comes up against naive ideas about evidence-based design and EBD and confusing juxtapositions about EBD against human experience that are not well developed as their definitions and value assumptions are poor at best, or hidden at worst ( Vaikla Poldma, 2003, Poldma 2010). I propose a broader knowledge-based approach centred on people and their experiences, and how design creatively responds to issues and situations that are dependant on understanding the issues at their core, hence a participatory and collaborative approach often situated in specific research done to suit the design/issue/problem at hand from the "ground up". EBD is apriori and assumes causal explanations at its core ( aka positivist or post-positivist) and cannot be used when problems are situated "from the ground up".
Hence I concur with Birger' position, Chuck's reaction and Ken's answer, which adds the broader dimension to how knowledge is constructed using evidence as the basis of research and as necessary to move professional forward. The problem is defining and situating EBD versus "evidence-based design approaches" and I have tended to stay away from the latter due to the positivist link to EBD.
The position of the researcher is key and the underlying values that they use to frame research questions are fundamental and these must be made explicit by the researcher and supported by the literature. This is the expectation in most disciplines such as medicine etc. For example, in the design disciplines, the values are ingrained in both art and science and from diverse perspectives and as such, the position of the researcher takes on various positions in various paradigms, depending on the questions asked. 
I propose a "knowledge-based" design research approach that accounts for the levels of paradigms that exist that underlie the value assumptions taken by design researchers, and position their value assumptions. In this type of approach, the design research accounts for both tacit (aposteriori) and evidence-based ( apriori) knowledge ( O'Brien, 2006). The roots of any knowledge are the positions of the researchers. In design we lack the foundations to explore design from the various perspective of knowledge constructions and this is still "in the making".
One of the flaws in design research is the lack of several practices common to other disciplines, including the positioning of historical precedent in knowledge-making and the positioning of values and knowledge constructions ( Friedman 1997, Friedman 2003). IN design research we need to document the ways we capture accurately and empirically the tacit knowledge we know moves design process and methods forward, the ways people use our designs, spaces, etc and what works and what does not, how we imagine "that which does not yet exist" and account for both ethical and service-oriented practices ( Nelson & Stolterman, 2012)  and the ways the specific disciplines creates knowledge through the various "tools" they use and how each approach must be empirically developed using the appropriate research methods or approaches. In the case of design, these include creative thinking, technological and methodological approaches, etc. and each one needs a knowledge position that is unique to design and the particular discipline within which the research occurs ( or within inter-or trans-disciplinary approaches). Too many use knowledges from other disciplines such as EBD, and too often not understanding the the value positions that underlie the approach taken. 
Regards to you all,
Tiiu 		 	   		  

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