In which of the following documents is it most appropriate to include an executive summary?

An executive summary is a concise overview of a larger document, designed to provide readers with a quick yet comprehensive understanding of the main points and findings. Including an executive summary is most appropriate in a complex research report because such reports typically present a significant amount of data and detailed analysis. The executive summary allows readers, who may not have the time or need to read the entire report, to grasp the essential information and conclusions quickly.

In contrast, while a six-page case study may benefit from a summary, it might not require the same depth of overview that an executive summary provides, given its shorter length. An employee handbook is primarily a reference document for policies and procedures, making an executive summary unnecessary. A manuscript outline usually serves as a planning tool without the need for an overview since it doesn't contain final content to summarize. Therefore, the complexity and detail inherent in a research report justify the inclusion of an executive summary to facilitate understanding of its contents.