Why Doesnt My Query Work

select distinct
a.Patients,
b.Patients,
a.pct,
b.pct

from
(
select count(*) as Patients, [pct of res] as pct
from testing
where [18 week wait] <= 18
group by [pct of res]
) as a right outer join
(select distinct[pct of res] from testing) as c on a.pct=c.[pct of res]and a.pct <> 'null' --is not null

(select count(*) as Patients, [pct of res] as pct
from testing
where [18 week wait] >18
group by [pct of res]
) as a left outer join as b on c.[pct of res]=b.pct