1 : careful or diligent search
2 : studious inquiry or examination; especially : investigation or experimentation aimed at the discovery and interpretation of facts, revision of accepted theories or laws in the light of new facts, or practical application of such new or revised theories or laws
3 : the collecting of information about a particular subject
From Merriam-Webster's Online Dictionary
Because IS is an interdisciplinary field, researchers use multilple methods, depending on the nature of the question, the data sources, the setting, the timeframe, and more. Some of the common methods include:
In the standard IS databases, the research method is sometimes indexed, but not routinely. If you're searching for studies that employed a particular method, try using the method as a keyword combined with your topic.
The methodology of a study may not be mentioned in the title of an article or its subject descriptors, but it's almost always mentioned in the abstract. Targeting your search to the abstract field when you're searching for particular methodologies is therefore usually successful.