Prepared by Elisabeth Lindsay.
For the purposes of genealogy, an indexer is a person, often a volunteer, who reads, analyzes, interprets, and transcribes information from documents that are to be incorporated into an index. The purpose of an index is to increase accessibility. Books, non-fiction books, in particular, often have alphabetical indexes that allow readers to easily find the subject and page for information they seek. Indexes are considered a derivative source, derived from other sources. People have been building indexes for generations, many are published in print and found in libraries. Today, indexes are created by indexers entering information into a computer database; once completed, the information (data) is becomes searchable and users can access it by entering keywords.
Indexers provide a valuable service to the genealogy community; the work is challenging at best, attempting to read and interpret handwriting in old documents. Typically, there are at least two people indexing a single document, with a third "moderator," available to address any conflict between transcriptions. Even with these controls in place, indexer error does happen. Many of the online databases have a feature allowing users to comment if a document appears to be in error. But because of the margin of error, it is important to verify information found in indexes (and other derivative source materials), especially where information is in conflict.