Lapizuli - 5:24 am on Aug 8, 2011 (gmt 0)
2) Does anyone have a theory on why there is that inconsistent holding?
If it's working as it should:
Because some synonyms are more synonymous than others, depending on the query.
"Pain medicine" turns up both pain reliever and pain relief bolded in the results. And they're more or less interchangeable in meaning as far as synonyms go, as long as you're not talking about the American Academy (Board?) of Pain Medicine (which makes up many of the page 1 results.)
A query for cocoa recipe turns up the bolded synonym hot chocolate. But note, not merely "chocolate". Why? Because cocoa could mean hot chocolate or the ingredient cocoa in this query, but is less likely to mean just "chocolate."
Similarly, the query cadbury milk won't have the synonym "dairy" bolded, because both "milk" and "dairy" in this context are all about the chocolate - they're not about each other.
Although using this logic, I'd kinda think milk allergy would include related terms "dairy" or "casein", but no. So maybe it has to do with the number of closely relevant results...? Or just data on how interchangeable the terms really are? I've often thought that terms which you'd think are interchangeable may very well not be. Like:
Google may "know" from the data that people typing in brown skirt want a brown skirt OR DRESS, but that people typing in skirt brown definitely want a skirt, ideally with some brown in it.