The comparison signs i.e. ">" do not work for score_<Objective>

I typed

/testfor @a[score_ModifyKills=<1]

(note that "ModifyKills" is a scoreboard objective)
When I gave myself -1 of ModifyKills, the comparator did not output anything. I tried with

 /testfor @a[score_ModifyKills=-1] 

and it outputted a comparator signal.