Level of English
Driver vs. Non-Driver
Years of Experience
Level of Education
Ability to Travel
Number of Children in the Family
Extent of Responsibilities
For example, if you are hiring someone who speak perfect English, drives, and has a vehicle for use on the job, holds 5-10 year experience, has a child-development degree and/or college education, is able to travel anywhere in the world, can care for 2 or more children at a time, is willing to do errands and light housekeeping as needed and when time permits, then we are looking at a top notch nanny who should be making minimum $22/hr.
Stepping down the ladder, we get the next level that is more available to most. A nanny who speak good English (but not excellent), drives, has 3-5 years of experience but little child-development education and no college credits, cannot travel outside of the country either because she doesn't want to or only has a work permit instead of a resident card or US passport, will care for 1-2 children and does housekeeping chores as time permits, would be paid $15-18/hr.
There are other variable that can play into a salary: at-home parents to assist with children, infant/toddler experience, driving (mileage and gas reimbursement), just to name a few.
I hope this helps! Feel free to email and/or call me if you have further questions.