Generally we use different methodology according to our subject requirement but some time we feel same methodology is used by 2 different authors and the finding are totally different.
It solely depends on your research purposes and research questions. Considering the research questions you take your methodological decisions. Thus, the choice is not on the basis of subject or discipline; rather, it is based on the research question(s). In order to answer your research questions, you employ certain research methodologies which ought to be the best fit to get the answer.
Research findings are not only depends on research methodology but also on other factors like culture of the respondents, technology used etc... hence results may vary , that is the reason you need to add this in limitation statements.
As Uday Bhale notes, there can be any number of factors that account for different results when suing seeming similar methods. From a practical standpoint, this generates a definite need for further research.