Which unique market research method was used to compile entries for the first Oxford English Dictionary in the 19th century?

The Oxford English Dictionary (OED) is one of the most ambitious lexicographical projects in history. Its development represents a fascinating story of dedication to language documentation. What began as a modest initiative evolved into a comprehensive record of the English language across centuries. This poll tests your knowledge about this iconic dictionary's creation process and the remarkable efforts behind documenting our language's evolution.

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Public crowdsourcing through an early form of 'citizen science' where volunteers submitted quotations on slips of paper
Exclusive research by Oxford professors who traveled throughout English-speaking countries conducting interviews
Analysis of existing dictionaries with minimal original research to create a composite reference
Automated collection from a mechanical card catalog system invented specifically for the dictionary project