Nonignorable

Although it is fundamental for valid statistical inference, identifiability under nonignorable missing mechanisms is not established for many commonly-used models.

"It's a brute force method," said Clifford Young, the president of U.S. public affairs at Ipsos. "That is, we don't really know what it corrects for. Does it correct for only nonignorable nonresponse? Or does it correct for coverage bias? Or maybe a likely voter problem? Maybe all three."