What is the effect of utilizing broader demographic targeting (e.g., age range) versus narrower interest-based targeting on overall CPA in a Yahoo! Japan campaign?

Utilizing broader demographic targeting (e.g., age range) generally leads to a higher cost per acquisition (CPA) compared to narrower interest-based targeting in a Yahoo! Japan campaign. Broader demographic targeting, such as targeting all users aged 30-50, reaches a larger audience, but it also includes many users who are not genuinely interested in the advertised product or service. This results in lower conversion rates because a significant portion of the audience is irrelevant. Lower conversion rates directly increase the CPA because the ad spend is distributed across a larger group, only a small fraction of which converts. Conversely, narrower interest-based targeting, such as targeting users who have shown interest in specific hobbies or products on Yahoo! Japan properties, focuses on a more qualified audience. These users are more likely to be interested in the ad, leading to higher conversion rates. Higher conversion rates, in turn, lower the CPA because a larger percentage of the targeted audience converts. For example, if you're selling high-end coffee beans, targeting all users aged 25-45 (broad demographic) will likely result in a higher CPA than targeting users who have visited coffee-related websites or searched for coffee brewing equipment on Yahoo! Japan (narrow interest-based). The interest-based audience is pre-qualified, increasing the likelihood of conversion and reducing the cost per acquisition. The key is that interest-based targeting improves relevance which drives conversion rates and lowers CPA, while broad demographic targeting casts a wider net that captures uninterested users, increasing CPA.