In two case studies, Marketing Experiments showed important the ad text is to both the click through rate and conversion rate. In one study that tested ads for Encyclopedia Brittannica, ad titles that contained both “Encylopedia” and “Brittannica” converted 2.5 times better than ad titles that contained only “Brittannica. ” It is important to understand that 90% of the tested traffic saw the ads after searching for a phrase that contained both terms.
This study quantified something that any sophisticated PPC advertiser probably already knows–you should try to match your ad titles as closely as possible to the search terms that you are buying. Be as specific as you can, using brand names if possible.
The second study involved an online newspaper and compared relevance between directly related keywords such as “online newspaper” to indirectly related keywords such as “Iraq.” Using indirectly related keywords generated traffic but with a much lower click through rate and conversion rate.
Of course, this study highlights something else that is very important. Traffic is not the key metric of most websites–but profitable traffic is. Only when monitoring the customer acqusition costs and customer values can you decide whether any keyword bidding (directly or indirectly related) makes sense. it is my guess that there are few industries where you can profitably bid on indirectly related keywords.