Why in proactive test Avast found only 5% of worms?(www.av-comparatives.org)

Why in proactive test of “av-comparatives” Avast 5.0.396 found only 5% of worms?
What happened?
Is really trust the test done by AV-Comparatives?
We worry about what happened?
Somebody give me some clarification. Thank you.

Link of test:
http://www.av-comparatives.org/images/stories/test/ondret/avc_report26.pdf

I believe there a couple of topics relating to this already, so I suggest you do a forum search for AV-Comparatives and order by most recent.