If by indirect methods you mean online, without the need for the student to be present in the classroom, then there is always the question about the impact it has on the learners
It sounds like you are on a start to an interesting study. To help us answer your question better though, can you tell us a bit more about what you are trying to discover? what are you seeking to understand about the methods? the impact on students before and after for instance?
This is a notoriously difficult area to determine anything meaningful that can be generalised. The number of variables associated with any form of Teaching/Learning are many.
My conclusions confirmed those of others: the differences arranged within any form of learning can exceed those between different forms of learning.
see page 90 Interactive Video: Rationale, Use and evaluation. D.Phil Thesis. University of Sussex 1987. Access from British Library EtHOS
If I correctly understand, in few words, you want to know if a direct/indirect teaching methods directly improves the learning process.
To me it sounds like an attempt to solve a "mission impossible".
I agree with Peter Copeland, it's very difficult to determine anything in that way.
Moreover, there is a numbers of authors demonstrated that the teaching/learning process depends on the general level of teacher-student fit (see Thomas & Chess' Goodness of fit Theory).
IMHO, perhaps you could adopt a quasi-experimental research design with the aim of evaluating the effects of direct and indirect
instructional strategies (not general teaching methods, or any kind of general teaching/learning strategies) on students‘ achievement in one (or more) specific discipline (s).
Alternately (in a survey oriented design) you could simply test the correlations among students' achievements and teachers' "constructivist vs bio-innatist (relating to genes)" approach to teaching. In this case literature offers some interesting scales on teachers beliefs.