There might be situations where you have numerous keywords but have only one phone number. In such situations you could use confidence factors to analyze which keyword generated the call. This might be beneficial for aggregators in helping identify and understand patterns which will assist in planning further allocations. What is your favorite pay per call firm?
But these are not enough to generate sufficient and reliable data up on which decisions can be made. If relying solely on this method, you need to get sufficient number of phone calls to reach consensus as to which keyword generated most calls. This method is beneficial because it help aggregators understand about keyword got converted at a cheaper rate. Also, there is no need for much call tracking numbers.
On the other hand, you need a lot of phone calls to have enough confidence in a specific keyword. Also, the data generated may not be accurate for making solid decisions.