Open-Ended versus Close-Ended Comparisons

Another relevant issue is whether conclusions and arguments should be spelled out explicitly in a comparative advertisement or whether the receiver should be left to draw his or her own conclusions about the superiority of the brand sponsoring the comparison.

It is often advantageous to leave something out of a message. Leaving
something out can stimulate curiosity and motivation to seek additional information about the brand and lead to a consumer-generated belief that is relatively more powerful than a belief created by an explicit statement in the ad. This would argue for not making explicit claims of the sponsoring brand’s superiority.
However, there is some risk in assuming that a receiver will “draw his own conclusions.”

Research suggests that conclusions should be stated explicitly when there is a significant chance that the audience will not be motivated or unable to draw their own conclusions, or when there are real risks of having them draw the wrong conclusions.

It was found that if the audience is involved in the message, and if the message is one where a conclusion can be easily drawn, an open-ended message (where no explicit conclusion was drawn) led to greater brand attitudes, intentions, and choice than a close-ended message (there was no difference for an uninvolved audience).

It was also found that comparative ads gain in relative effectiveness when aimed at more expert consumers and when they make comparison with specific, well known brands, because the comparative ad can be interpreted more ambiguously under these conditions.