The 1996 figure was 17%.
Thanks for the research, Poohbah.
After looking at the poll, I would estimate the MOI to be around 7%. Repeatedly there is a non-sensical 5% on polarizing questions such as (not really an example, but for demonstration of some of the responses) "Who would make the better President?" who answered one candidate and voted for the other.
And that consistent 5% of illogical answers doesn't even account for the statistical error in extrapolating results from a sample across the entire voting population.