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Why do truncation (*) searches sometimes return fewer results?

Truncation searches using an asterisk (*) allow the EBSCO search engine to expand the query into multiple possible keywords. In some circumstances using the * operator can return fewer results. For example: The search “pediatric* and nursing” vs “pediatrics and nursing”. The truncated query returns 4322 results while the non truncated query returns 5525 results.

The root of the issue comes from a behind the scenes feature of the EBSCOhost search engine that applies a generic default thesaurus to searches (i.e. different forms and tenses of a word, even British spelling alternates).

As a rule we have never applied default thesaurus terms to truncation searches. This is why some phrases can return fewer hits. In this specific circumstance when a user searches for (pediatrics) we also search for the alternative spelling (paediatrics) found in the default thesaurus. However when the user searches for (pediatrics*), we never consult the thesaurus so "paediatrics" is not returned and you get fewer results. The reason we have not used the default thesaurus for truncation searches is that the stem could have too many possible keyword combinations with which to apply the thesaurus after they are generated.

In the coming months we will explore enhancing this functionality: If the stem of the truncation search is in the default thesaurus, then apply synonyms. Heart attack* would search “myocardial infarction” but heart attac* would not. pediatric* would search “paediatrics” but pediatri* would not.

Please note, this behavior does not apply to all EBSCOhost databases. For example, because the CINAHL default thesaurus does not employ plural and possessive forms, this behavior does not apply to truncated searches in those databases.