Contemporary reasoning about health is infused with the work products of experts,
and expert reasoning about health itself is an active site for invention and design.
Building on Toulmin's largely undeveloped ideas on field-dependence, we argue that
expert fields can develop new inference rules that, together with the backing they
require, become accepted ways of drawing and defending conclusions. The new inference
rules themselves function as warrants, and we introduce the term "warranting device"
to refer to an assembly of the rule plus whatever material, procedural, and institutional
resources are required to assure its dependability. We present a case study on the
Cochrane Review, a new method for synthesizing evidence across large numbers of scientific
studies. After reviewing the evolution and current structure of the device, we discuss
the distinctive kinds of critical questions that may be raised around Cochrane Reviews,
both within the expert field and beyond. Although Toulmin's theory of field-dependence
is often criticized for its relativism, we find that, as a matter of practical fact,
field-specific warrants do not enjoy immunity from external critique. On the contrary,
they can be opened to evaluation and critique from any interested perspective.