I imagine it depends on definitions. I bought a dozen pairs of socks in November; does that count as 12 pieces of clothing or 24 pieces of clothing? Do the hiking boots I bought count as clothing? And if a new parent is buying baby clothes, who is the consumer -- the parent or the baby?
The latter point is probably not as important since we're talking about averages anyway.
I would imagine boots do not count since we're talking about detergent here, although some shoes can be thrown into the washing machine.
There are three comments about socks now :-) But to get to 68 you'd still have to buy 34 pairs of socks. Even if you exchange some of them for shirts, pants and underwear, you'd need a pretty big sock drawer if you keep adding and adding every year...
I throw away socks as soon as they get holes in, which is pretty frequent (I don't make any effort to take care of them, they're just socks). To replace them I buy a set of 5 pairs maybe three or four times a year. It doesn't seem completely implausible.
The latter point is probably not as important since we're talking about averages anyway.
Well, unless you say that the baby isn't a "consumer", in which case your average is the same total number of items of clothing divided by a smaller number of consumers.