How many {has effect} are to/by {bronchitis} ?
Bronchitis affects how many people?
How many are affected by bronchitis?
SELECT ( COUNT ( ?e ) AS ?f ) { ?e property:has_effect resource:bronchitis }
SELECT (COUNT(?sub) AS ?subs ) {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> ?sub .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P1542> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> http://wikidata.dbpedia.org/resource/Q173022 .
} 

SELECT (COUNT(?sub) AS ?value ) { ?sub wdt:P1542 wd:Q173022 }
12