Drunk parents

According to a recent Norwegian survey, half of young Norwegians
in the age group 12- 19 have seen at least one of their parents drunk.

I was quite surprised.
I never saw my own parents drunk.
As a teenager I never saw any of my friends' parents drunk.

Then I think about the survey:
What is the definition of drunk?
How drunk were these parents?
How often are they drunk?
Do they try to hide it from their children
or is it an open thing in their homes?

From my point of view:
If a person likes the taste of alcoholic drinks, I can understand
if he/she drinks a little, to enjoy the taste.

But the notion that persons who are , I hope, not alcoholics,
should choose to be drunk, is strange to me.