Call tracking for online content items

A system comprising:

• one or more processors configured to interact with a computer storage medium in order to perform operations comprising:
• determining a rank score for an online content item, wherein the online content item includes a phone number, and wherein determining the rank score comprises:
• for each call of a plurality of phone calls to the phone number, attributing the call to an online content interaction of a plurality of different online content interactions, wherein each online content interaction refers to a delivery of the online content item to a particular client device at a particular time,
• determining a probability of a call using the online content interactions attributed to the phone calls, wherein the probability estimates the probability that a future online content interaction will result in a call to the phone number, and
• using the probability of a call in determining the rank score for the online content item;
• determining, using the rank score, whether to provide the online content item to a client device;
• and
• providing the online content item to the client device upon determining to do so using the rank score.

A computer storage medium encoded with a computer program, the program comprising instructions that when executed by data processing apparatus cause the data processing apparatus to perform operations comprising:

• determining a rank score for an online content item, wherein the online content item includes a phone number, and wherein determining the rank score comprises:
• for each call of a plurality of phone calls to the phone number, attributing the call to an online content interaction of a plurality of different online content interactions, wherein each online content interaction refers to a delivery of the online content item to a particular client device at a particular time,
• determining a probability of a call using the online content interactions attributed to the phone calls, wherein the probability estimates the probability that a future online content interaction will result in a call to the phone number, and
• using the probability of a call in determining the rank score for the online content item;
• determining, using the rank score, whether to provide the online content item to a client device;
• and
• providing the online content item to the client device upon determining to do so using the rank score.