Just how do you link TV spots to phone calls?
The traditional method in direct response world is if a consumer calls within a specified window then there is direct attribution. On home-shopping programs this link is explicit, but as one moves from tight integration to looser programs uncertainty creeps in to the equation. Often one might use a limit of 15 or 30 minutes. But certain high-consideration products and possibly some cultures may require discussion and consensus before the call is made. So even if the call-to-action is simply requesting more information, it may be days before the call is actually made.
Understanding the decision making process is important in defining the business rules for attribution across media channels.