What type of data is often used to fill gaps in primary research?

The correct choice is secondary data because this type of data is collected by someone other than the user for purposes other than the original research. In the context of filling gaps in primary research, secondary data provides previously collected information that can help researchers better understand their topic, validate or compare findings from primary research, and provide additional context.

Secondary data often includes academic articles, government reports, industry publications, and datasets that can enhance the depth of analysis. Researchers frequently use this existing information to corroborate their primary findings or provide a broader framework for their research.

In contrast, while proxy data may serve a similar purpose, it refers specifically to indirect measures used to estimate values when direct data are not available. Random data and meta-data do not serve this function; random data is typically unsystematic and can lead to unreliable conclusions, while meta-data is data about the data, providing information on how to interpret or manage the data but not filling research gaps in the same way secondary data does.