Check how search engines see your website!
I just found out that search engines see http://www.websearchtechniques.com and http://www.websearchtechniques.com as different websites.
To set up a permanent redirect (technically called a “301 redirect”) I add the code:
RewriteEngine On
RewriteCond %{HTTP_HOST} ^example.com
RewriteRule (.*) http://www.example.com/$1 [R=301,L]
to the file .htaccess.
Problem solved.
It never occurred to me that http://www.website.com and website.com are perceived by search engines as two different sites.