You can use this online ClinCalc sample size calculator to determine what sample size is needed in a study to achieve enough power for statistically significant findings. These are designed for researchers to use, but journalists can use them if they have questions about whether a study has enough participants for the findings to be meaningful.
For one perspective on understanding of how researchers develop a priori hypotheses for systematic reviews, this paper discusses different ways of framing research questions: Methods Commentary: Framing the Question and A Priori Hypotheses.
While the concept of single- and double-blinding in studies seems pretty straightforward, it’s anything but in actual practice. In this article, “Blinding in pharmacological trials: the devil is in the details,” the authors discuss in depth some of the challenges and limitations to consider in designing drug trials with respect to blinding.