We were asked to describe the characteristics and differences between the NGT and Delphi models of research. This is my take on the differences, which model I would use and why.
The Classical Delphi model uses the anonymity of the participants allowing them to freely express their opinions without undue social pressures of having to conform to others in the group with decisions bases on merit, rather than who proposes the idea. Whereas, the NGT method limits participants the opportunity to comment on issues that were not covered in surveys and uses focus groups to encourage participants with one or two members that hold strong opinions influencing others and stifling ideas and evaluating factors identified by learners as positive and negative points.
From the readings the NGT method is mainly directed towards the medical field evaluating medical courses. The Delphi method, working with qualitative and quantitative methods seems to be more suited to Information System (IS) research because of its fluidity in its discipline and its flexibility when knowledge about a task is limited.
As for which method I would use from what I have read and think understand, the use of a modified Delphi in a closed or open collaboration would depend on the type of research one wants to accomplish. It seems that a closed collaboration would lead to a specific outcome for a specific study whereas an open collaboration would be used as sort of a brainstorming study to provide a generalized idea or direction in which to proceed.
A Modified Delphi Approach to a New Card Sorting Methodology http://usabilityprofessionals.org/upa_publications/jus/2008november/JUS_Paul_Nov2008.pdf