Is a comparative advertisement more effective than a non-comparative one? Much research has focused on this question, and the evidence on greater effectiveness is often equivocal. The results seem to vary not only upon the specific kind of comparative ad used and the brands involved, but also on the measure of effectiveness used (attention/recall, perceived similarity, or persuasion) and even the specific questionnaire scales used to measure effectiveness.

The effectiveness of comparative ads sometimes lies not in raising the preference ratings of the advertised brand, but in lowering the preference ratings of the comparison brands, or even in simply increasing the perceived similarity of the advertised and comparison brands without affecting any preference measures at all. It is thus important, in copy testing or tracking the effectiveness of comparative ads; to measure beliefs and preferences not only toward the advertised brand but also toward competition, as well as measure perceived similarities among these brands.

If attention and recall are used as the measures of ad effectiveness, various studies have shown that comparative ads do usually get more attention and higher recall than non-comparative ads. Pontiac used comparative advertising for its Grand Am in 1992, comparing it to the Toyota Camry and Honda Accord, because they found focus groups reacted more strongly to comparisons with specific competitors than to unnamed imports. Naveen Donthu found the gain in recall was highest if the comparisons being made were more “intense” (naming explicit competitors, making comparisons on specific attributes, and only making a one-sided claim).