If they are too narrow, then two few results are returned. Synonyms can provide the right level and ensure proper coverage. Use the Boolean OR to string synonyms together. Examples female OR women teenagers OR adolescents Check to make sure you are not using redundant terms. Example peregrine falcon, bird Phrases target results.
Phrases are a powerful search technique.
They require that all terms appear in the exact order shown. Use AND to glue your search terms together. The Boolean AND focuses a search by retrieving only those records that contain at least one term or phrase from each concept. The capitalized form will work for all engines. Limit AND to three or fewer.