Which aspect must be documented for compliance during study execution?

Documenting signed informed consent from subjects is crucial for compliance during study execution because it serves as a key ethical and legal requirement in clinical research. Informed consent is designed to ensure that participants are fully aware of the study's purpose, procedures, potential risks, and benefits before agreeing to take part. This documentation not only protects the rights and welfare of participants but also holds the research team accountable to regulatory standards. It is a tangible record that the study has upheld ethical practices and that participants have voluntarily participated in the research.

The other options, while relevant in specific contexts, do not have the same foundational role in ensuring compliance with regulations aimed at protecting human subjects in research. Financial reports and communication with regulatory bodies such as the FDA are important for the administration and oversight of the study, but they do not pertain directly to the ethical considerations surrounding the treatment of participants. Similarly, reviewing previous studies is beneficial for designing new research but is not documented as part of participant consent and protection during the execution of a current study. Therefore, signed informed consent is the critical piece of documentation required for compliance.