Theory of Creative Practice is an emergent field that is generally considered to be situated in the Humanities; however this may be an incomplete definition since the field is hybrid in nature and may borrow from many different research methodologies, some of which may not relate to the Humanities but to different types of inquiry. This may especially be the case for design projects that can often be evaluated under quantitative approaches to benchmark or assess their functionality. Below are the global definitions for two pervasive research methods (Quantitative and Qualitative), followed by a definition of a novel field called Digital Humanities that may also carry some relevance when it comes to theorizing upon ToA/CP projects that can be linked to computational visualization or archiving systems.

Quantitative research refers to the systematic empirical investigation of social phenomena via statistical, mathematical or computational techniques. Quantitative data is any data that is in numerical form such as statistics, percentages, etc. This means that the quantitative researcher asks a specific, narrow question and collects numerical data from participants to answer the question. The researcher analyzes the data with the help of statistics, hoping that the numbers will yield an unbiased result that can be generalized to some larger population. Quantitative research is used widely in social sciences such as psychology, economics, sociology, and political science, and less frequently in anthropology and history. Research in mathematical sciences such as physics is also 'quantitative' by definition, though this use of the term differs in context. In the social sciences, the term relates to empirical methods, originating in both philosophical positivism and the history of statistics. 

Qualitative research is a method of inquiry employed in many different academic disciplines, traditionally in the social sciences, but also in market research and further contexts. Qualitative researchers aim to gather an in-depth understanding of human behavior and the reasons that govern such behavior. The qualitative method investigates the why and how of decision making, not just what, where, when. Qualitative methods produce information only on the particular cases studied, and any more general conclusions are only propositions (informed assertions). Quantitative methods can then be used to seek empirical support for such research hypotheses. 

There is no agreed ‘industry standard’ or prescribed process for approaching a qualitative project but there are some recognized strategies and steps you can take such as exploring the perceptions of others through interviews and questionnaires, and conducting solid literature reviews. Qualitative research is by definition exploratory, and it is used when we don’t know what to expect, to define the problem or develop an approach to the problem. It’s also used to go deeper into issues of interest and explore nuances related to the problem at hand.

An area that may also be related to Theory of Artistic/Creative Practice (especially if you are coming from a computational background) is Digital Humanities that covers research, teaching, and creation concerned with the intersection of computing and the disciplines of the humanities, embracing a variety of topics ranging from curating online collections to data mining large cultural data sets. Digital Humanities currently incorporates both digitized and born-digital materials and combines the methodologies from the traditional humanities disciplines (such as history, philosophy, linguistics, literature, art, archaeology, music, and cultural studies) with tools provided by computing (such as data visualisation, information retrieval, data mining, statistics, computational analysis) and digital publishing. Another goal is to create scholarship that is more than texts and papers. This includes the integration of multimedia, metadata and dynamic environments. Digital humanities is also involved in the creation of software, providing "environments and tools for producing, curating, and interacting with knowledge that is 'born digital' and lives in various digital contexts. 

Further reading:
http://www.icoe.org/webfm_send/1936
http://www.surveygizmo.com/survey-blog/quantitative-qualitative-research/
http://www.researchproposalsforhealthprofessionals.com/quantitative_research_design.htm
http://commons.gc.cuny.edu/wiki/index.php/The_CUNY_Digital_Humanities_Resource_Guide