Doesn't seem so. If you rate by quintiles your rating effectively indicates the rank of the bucket to which the thing-being-rated belongs. This reflects "the item's relative position in its group".
If you want your rating to reflect not a rank but something external, you can set up a variety of systems, but I would expect that for max information your rating would have to point a quintile of that external measure of the "value independent of the group".
Trying to stab at the heart of the issue: I want the distribution of the ratings to follow the distribution of the rated because when looking at the group this provides an additional piece of information.
This thread is for asking any questions that might seem obvious, tangential, silly or what-have-you. Don't be shy, everyone has holes in their knowledge, though the fewer and the smaller we can make them, the better.
Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.
To any future monthly posters of SQ threads, please remember to add the "stupid_questions" tag.