Coupon used (statistics)

Hi,
On my homepage I have a list of coupons shown. Underneath the description you can see some statistics like number of times used, expiry and succesrate. (see attachment).
The number of times used does not seem to change from 0 no matter how many visitors have clicked on the coupon.
In the extra fields ( when you create a new coupon) there is no field that can manually change the contents of this field either.
It looks very strange having all your coupons 0 times used by visitors.