help with SQL conditional report

i have a table (stacked) with variables cipcode, awlevel, unitid, and year.  

im trying to generate a report that will tell me the distinct count of unitid where awlevel=5 and cipcode=45.0601 in 2001 but not 2011.  Basically i need results where cipcode only exists when year=2001 and doesnt exist when year=2011.

so far i have this, which gives me the results for 2001 only

	select count(distinct(unitid)) as Grad11 label="Schools with Graduations",
	from stacked
	where awlevel=5 and cipcode='45.0601' and year=2001;

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I think the answer involves nested selects but i cant wrap my head around it.