Someone told me that the average number of legs in the human population is less than 2, because there are more amputees than those with multiple limbs. I found it odd at the time (a statistics teacher told me it), but now it got me thinking. Has anyone actually measured this?
In the United States, there are approximately 1.7 million people living with limb loss. It is estimated that one out of every 200 people in the U.S. has had an amputation.
Many of those without limbs are missing arms, not legs. To figure out the number of missing legs, you will need to do a bit of data-crunching - they have figures of upper versus lower-body limbs, but they are generally not given per capita, but per hospital discharge, by cause, so you will need to multiply these out.
Further, if a person has multiple amputations of the same limb (at different points) that will confuse the averages, but that should be close enough for your needs.
(When you have finished using their figures, perhaps you should consider donating to the organisation that produced them.)