Which of the following is a key metric for evaluating conversion effectiveness?

Cost per lead is indeed a key metric for evaluating conversion effectiveness because it directly measures the cost associated with acquiring a potential customer who has shown interest in a product or service. This metric provides insights into how efficiently a campaign is converting potential customers at various stages of the sales funnel. Lowering the cost per lead while maintaining or increasing the quality of leads reflects effective targeting and messaging in a media buying strategy.

While other metrics like clickthrough rate, messaging conversations started, and phone calls placed can provide valuable insights into engagement and interaction, they do not directly address the conversion aspect. Clickthrough rate focuses on initial engagement rather than the actual conversion. Messaging conversations and phone calls may indicate interest, but they don’t capture the relationship between cost and lead generation. Therefore, cost per lead is the most relevant metric for assessing the true effectiveness of conversions in a media buying context.