The focus of qualitative research is observation. When looking at a painting, a qualitative researcher would notice the colors used, the scene and how the frame feels. This approach is influenced by the observer, as observation is often biased. Qualitative research is also deductive in that it begins with generalizations and then draws conclusions from those generalizations. For example, this artist painted a beautiful painting; therefore, this artist must have painted other beautiful paintings.
Quantitative research is concerned with measurable data. Looking at the same painting as the qualitative researcher, the quantitative researcher would notice how much it weighed, its length, width and depth and the materials involved. This method is considered more scientific because it involves scientifically supportable data. This approach is inductive; it takes a series of facts and draws a conclusion based on those facts. For example, each of this artist's paintings are beautiful; therefore, all paintings by this artist are beautiful.
In a research paper, the subject often determines the content. Research papers of scientific disciplines such as biology or astronomy will likely be exclusively quantitative in nature. In the humanities, the line may be blurred, or the paper may just be qualitative. However, both categories may be approached either way. Which approach the writer uses should be clear in the thesis statement, which is the statement being either supported or refuted.
To argue the superiority of one approach over the other is problematic because the argument is mainly a philosophical one. However, it is also difficult to argue that research should include both. In his article "Mixing Qualitative and Quantitative Methods: Triangulation in Action," Jick comments that those who advocate for triangulation -- a mixture of the two -- "fail to indicate how [it] is actually performed."