how do you compute the variance long duration call average duration of call how to calculate the long-duration variance the average length of calls should be how to calculate mean and variance of telephone calls how to find average phone call length what is the variance of a phone call how do you find average length of call average duration of a call how do you calculate the long duration of a call what is the variance of the long and short duration calls? how to calculate long duration phone calls how to do the variance for long duration calls how many long duration calls are there in call centre data? what is the difference between long and short duration calls which is the best way to measure the variance of long time calls? how to calculate the variance of call calls how to find duration of long duration calls how to calculate average long duration telephone call how to calculate long and short duration of call