Ross believes that personality development is a matter of sudden qualitative changes at various turning points in the life span. his viewpoint is most directly relevant to the issue of

Ross viewpoint is most directly relevant to the issue of continuity and stages.
Continuity because the development is a gradual and continuous process (personality development is a matter of sudden qualitative changes) .
Stages because the discontinuity theory says that development occurs in a series of distinct stages. (various turning points in the life span).

The best sociological research method would have to be using experiments although it has some disadvantages as well