Is it really true that 50% of Americans don't believe in Evolution?

I venture that >90% of Americans don't know what they truly believe. We say we belive A or B or even C, but if pressed hard, we are apt to change our minds. Likewise, too much of what we believe is dictated not by reasoned decision, but by default, accident or b/c it has been fed to us. Social Psychology strongly suggestes that what people believe and how they behave is too often at odds; likewise, what is believd is easily swayed if others disagree b/c of our herd behavior (desire to fit in). In the end, it doesn't sem to matter since the herd behavior mentality appears to dictate for most!