Which of the following is categorized as a secondary research source?

Secondary research sources are those that analyze, interpret, or summarize information originally presented in primary sources. Newspapers are categorized as secondary research sources because they often report on events, research findings, and other information that has already been generated by primary sources or firsthand accounts. In this context, articles typically synthesize information from various primary sources, making them secondary.

While personal letters, speeches, and statistical data can be valuable in research, they often serve as primary sources. Personal letters provide direct insights into an individual's thoughts or experiences, speeches represent firsthand communication from the speaker, and statistical data often reflects original research findings or raw data collection. Therefore, newspapers are the best example of a secondary research source among the options.