Research Questions and Depth

With the inexorable rise in the number of PhD students worldwide, it seems inevitable that the approval of PhD proposals and the reporting of progress becomes somewhat mechanistic. In determining whether a student is making sufficient progress we tend to ask whether the student has identified their research question or hypothesis, whether the literature review is underway etc.
In this posting I want to propose some criteria to help determine whether a given research question is likely to prove a sufficient basis for PhD rseearch.
A good research question should be one whose answer would be recognised as a contributon to knowledge in the subject discipline concerned. For this purpose, the terms of the research question should implicitly or explicitly

• identify an area of knowledge in the discipline where knowledge is known to be partial
• pose a question whose answer would fill a gap in that knowledge
• give a means of evaluating the evidence obtained during the student's investigation

Thus, if readers of the research proposal consider that the answer to the research questions is already known in the discipline, or would not be of interest, then the research question needs to be replaced by one whose investigation will be more fruitful.
Most academic disciplines contain numerous areas where knowledge is known to have gaps, and a good research question should be expressed in terms that are sufficiently tightly defined to specify a suitably narrow area for investigation, preferably where some established methodologies would be recognised as useful. If the research question is no more precise than the title of theresearch, or merely indicates the discipline itself, then it does not meet this criterion.
Examples of bad research questions would trivially include:

• Can further investigation of X yield useful results?
• Are existing mechanisms for Y sufficient to achieve Z?

The objections to research questions of this type are twofold: First,  they are insufficiently precise: what sort of further investigation? useful in what way? which existing mechanisms? achieved in what way or to what extent? etc etc Second, the answers are almost always trivial: Yes and No respectively. Research questions of the form Which, what, why or how? would (always?) be more promising than those listed.
At the very least, the subject area outlined in the title of the research should be refined to indicate what aspects of the current state of knowledge are considered promising for the establishment of a contribution to knowedge (to have gaps).
Of course, the research question precedes the full literature review, where a more detailed review of the existing state of knowledge will be undertaken. The research question is intermediate in detail between the title, and the section giving dtails of the proposed investigation (research methodology). It should represent some progress on the title, and should be suitable for inclusion in some form in the abstract.