elucidate within-group variability, which can only be done if the hierarchy of evidence is replaced by a network that takes into account the relationship between epidemiological and laboratory research" the hierarchy of evidence produced by a study design has been questioned, because guidelines have "failed to properly define key terms, weight the merits of certain non-randomized controlled trials, and employ a comprehensive list of study design limitations". stegenga has criticized specifically that meta-analyses are placed at the top of such hierarchies. the assumption that rcts ought to be necessarily near the top of such hierarchies has been criticized by worrall and cartwright. in 2005, ross upshur noted that ebm claims to be a normative guide to being a better physician, but is not a philosophical doctrine. he pointed out that ebm supporters displayed "near-evangelical fervor" convinced of its superiority, ignoring critics who seek to expand the borders of ebm from a philosophical point of view. borgerson in 2009 wrote that the justifications for the hierarchy levels are not absolute and do not epistemically justify them, but that "medical researchers should pay closer attention to social mechanisms for managing pervasive biases". la caze noted that basic science resides on the lower tiers of ebm though it "plays a role in specifying experiments, but also analysing and interpreting the data." concato argued in 2004, that it allowed rcts too much authority and that not all research questions could be answered through rcts, either because of practical or because of ethical issues. even when evidence is available from high-quality rcts, evidence from other study types may still be relevant. stegenga opined that evidence assessment schemes are unreasonably constraining and less informative than other schemes now available. in his 2015 phd thesis dedicated to the study of the various hierarchies of evidence in medicine, christopher j blunt concludes that although modest interpretations such as those offered by la caze's model, conditional hierarchies like grade, and heuristic approaches as defended by howick et al all survive previous philosophical criticism, he argues that modest interpretations are so weak they are unhelpful for clinical practice. for example, "grade and similar conditional models omit clinically relevant information, such as information about variation in treatments’ effects and the causes of different responses to therapy; and that heuristic approaches lack the necessary empirical support". blunt further concludes that "hierarchies are a poor basis for the application of evidence in clinical practice", since the core assumptions behind hierarchies of evidence, that "information about average treatment effects backed by high-quality evidence can justify strong recommendations", is untenable, and hence the evidence from individuals studies should be appraised in isolation.