  Empirical evidence has confirmed that quantum effects occur frequently also
outside the microscopic domain, while quantum structures satisfactorily model
various situations in several areas of science, including biological, cognitive
and social processes. In this paper, we elaborate a quantum mechanical model
which faithfully describes the 'Ellsberg paradox' in economics, showing that
the mathematical formalism of quantum mechanics is capable to represent the
'ambiguity' present in this kind of situations, because of the presence of
'contextuality'. Then, we analyze the data collected in a concrete experiment
we performed on the Ellsberg paradox and work out a complete representation of
them in complex Hilbert space. We prove that the presence of quantum structure
is genuine, that is, 'interference' and 'superposition' in a complex Hilbert
space are really necessary to describe the conceptual situation presented by
Ellsberg. Moreover, our approach sheds light on 'ambiguity laden' decision
processes in economics and decision theory, and allows to deal with different
Ellsberg-type generalizations, e.g., the 'Machina paradox'.
