The phrase "already existing research sample" is correct and usable in written English.
It can be used when referring to a research sample that has been previously established or collected in prior studies.
Example: "In our study, we utilized an already existing research sample to analyze the effects of the new treatment."
Alternatives: "pre-existing research sample" or "previously established research sample".
Data were collected by conducting semi-structured interviews with 8 dentists identified as a subgroup of an existing research sample.
But until January 2001, when the Dresden facility was completed, the already existing research groups worked in labs in Heidelberg, Berlin, Göttingen and Seattle.
We knew already from our existing research that the underlying evidence was insufficient to establish the best methods for managing these fractures.
The laboratory was not intended to reproduce the already existing Xerox research laboratory in Rochester, New York, that worked on refining and expanding the company's copier business.
Potential research questions are shown in italic red type and questions that were already being addressed by existing research are shown in bold red type.
All individuals have been informed of the analyses, and they have given written consent to use their already existing DNA samples.
Asking research participants to donate a sample or data for each research question when new research questions could potentially be answered by already existing samples and data is unnecessary duplication and unfair.
However, the existing research is largely limited to samples of former professional athletes and has a number of methodological concerns.
Thus, risk estimates were not adjusted for any impairment of kidney function already existing before the sampling.
Scoping reviews allow the researcher to (1) clarify working definitions and conceptual boundaries of a topic area, (2) outline what is already known and identify gaps in existing research, and (3) map existing literature of existing evidence.
