Final answer:
The two main considerations when selecting controls from a secondary study base are conducting an internal review to assess the consistency and reputation of the source and undertaking a literature review to understand the existing body of research.
Step-by-step explanation:
When selecting controls from a secondary study base, the two main criteria or considerations researchers go through are internal review and literature review.
An internal review involves examining if information in one source is supported or contradicted by other sources. This can include a subject search of the author across different platforms to understand how other experts view the author and to see how the source fits in with the author's other works. Evaluating the cultural value placed on appearance can be part of this review when considering controls related to health and social studies.
The next step is a comprehensive literature review, which includes conducting background research through academic journals, library resources, and thorough online searches to uncover existing research related to the study topic. This process helps in understanding work previously done, identifying gaps, and positioning new research to build upon existing knowledge.