Multimethod research entails the application of two or more sources of data or research methods to the investigation of a research question or to different but highly linked research questions. Such research is also frequently referred to as mixed methodology. The rationale for multimethod research is that most social research is based on findings deriving from a single research method and as such is vulnerable to the accusation that any findings deriving from such a study may lead to incorrect inferences and conclusions if measurement error is affecting those findings. It is rarely possible to estimate how much measurement error is having an impact on a set of findings, so that monomethod research is always suspect in this regard.
Multimethod Research
http://www.referenceworld.com/sage/socialscience/mmr.pdf
Multimethod research is undoubtedly being used increasingly in social research. Its appeal lies in the possibilities it offers in terms of increasing the validity of an investigation. It can be employed within and across research strategies and as such is a flexible way of approaching research questions, though it carries certain disadvantages in terms of time and cost. Multimethod research and multistrategy research in particular can present problems of interpretation, especially when findings are inconsistent, but the preparedness of researchers to address such problems will enhance the credibility of their work.