Which of the following is NOT a type of research strategy?

A controlled study is a research design that refers to how variables are managed and compared in experimental research but does not constitute a distinct research strategy on its own. In contrast, the other options represent recognized forms of research strategy.

Qualitative research focuses on understanding human behavior and the meaning individuals ascribe to their experiences, employing methods like interviews and participant observations. Mixed methods combine qualitative and quantitative approaches, leveraging the strengths of both to provide a more comprehensive analysis of research questions. Descriptive research, on the other hand, is a strategy utilized to systematically describe and document characteristics, often using surveys or observational techniques to gather data about a population or phenomenon.

This distinction between being a specific type of research strategy and merely representing an element of design helps clarify why controlled is not classified as a research strategy.