[NittanyLion]

Finally, let's look at the most weighty question: The preference as to Democrat-controlled versus Republican-controlled Congress. The survey reports this as: 37% preference for a Republican-controlled Congress, and a 52% preference for a Democrat-controlled Congress. Again, the 16% skew in the sampling in favor of Democrats renders these results completely incompetent. Making the adjustment as before, the results change stunningly: 45% voice a preference for a Republican-controlled Congress, and 44% for a Democrat-controlled Congress.

Your numbers don't work out. I ran the numbers assuming 85% of each party prefer that party in power, 5% are unsure, and 0% prefer the other party (historically this is accurate). Under those assumptions it's evident that self-identified independents prefer a Democrat-controlled Congress by a 2-1 ratio.

Now, if we assume the actual electorate will be 35% GOP / 35% DEM / 30% IND (again, historically that's accurate), then the adjusted results would be as follows:

Preference for GOP-controlled Congress: 38%
Preference for DEM-controlled Congress: 47%
Not Sure: 15%

As others have stated, you can't take percentages of percentages and expect it to work out. You have to convert the percentage into real terms, adjust the numbers, then reconvert it back into percentage format. Sorry.

[NittanyLion]

Oops - "and 0% prefer the other party" should be "10% prefer the other party".

[justshutupandtakeit]

You can figure out the degree of oversampling from percentages just as well as from the raw numbers from whence the percentages are calculated.

The point is that looking at 43% as only 6% greater than 37% is an invalid way of determining oversampling.