  Expert judgment for software effort estimation is oriented toward direct
evidences that refer to actual effort of similar projects or activities through
experts' experiences. However, the availability of direct evidences implies the
requirement of suitable experts together with past data. The
circumstantial-evidence-based judgment proposed in this paper focuses on the
development experiences deposited in human knowledge, and can then be used to
qualitatively estimate implementation effort of different proposals of a new
project by rational inference. To demonstrate the process of
circumstantial-evidence-based judgment, this paper adopts propositional
learning theory based diagnostic reasoning to infer and compare different
effort estimates when implementing a Web service composition project with some
different techniques and contexts. The exemplar shows our proposed work can
help determine effort tradeoff before project implementation. Overall,
circumstantial-evidence-based judgment is not an alternative but complementary
to expert judgment so as to facilitate and improve software effort estimation.
