Page 10 of the new Preach My Gospel:
Your success as a missionary is measured primarily by your commitment to find, teach, baptize, and confirm people and to help them become faithful members of the Church who enjoy the presence of the Holy Ghost.
Avoid comparing yourself to other missionaries and measuring the outward results of your efforts against theirs. Remember that people have agency to choose whether to accept your message.
There it is in black and white.
I am still surprised at how many missionaries, ward mission leaders, bishops, stake presidents, and mission presidents measure their success by baptisms alone.
But how else would you go about measuring commitment??Ç¬† Why the need to measure in the first place?