I recently moved from having a main site like
www.example.com with a subdomain associated site
yyy.example.com, to moving everything off the subdomain to a subdirectory like
www.example.com/yyy/, with the same hierarchy underneath the subdirectory, and now
yyy.example.com is just a redirect page to the subdirectory, so
yyy.example.com/abc/page-x is redirected to
www.example.com/yyy/abc/page-x and so on.
The effect has been that the traffic increased by several times (the total page views are more than ten times at the present rate) what it was to the
yyy subdomain. Previously almost all of the traffic to the
yyy subdomain was from the
www site. This is from monitoring the old
yyy site for a year or more.
I'm curious to know if there's any research or results which would indicate whether this is universal (subdirectories beat subdomains) or "just me".