dialout group missing

I have debian8, (Jessie) and I am trying to add a user to the dialout group. Alas, that group doesn't exist. I would prefer not to add the user to the root or sudo group.

what should I do?

~$ groups
user1 user2 cdrom floppy sudo audio dip video plugdev netdev lpadmin scanner bluetooth

How can I create the dialout group?

$sudo usermod -a -G dialout user1

executes without error, but I cannot see that I am a member of the dialout group, nor that any dialout group exists