as bad

as bad. or worse than… / as good or better than…

are examples of mixed constructions in which an element, in this case the second as (as bad as, as good as) has been omitted. It is common, especially in spoken English, but it is incorrect and should be avoided. The sentence We're sure they can judge a novel just as well if not better than us (London Review of Books, 1987) should be corrected to just as well as, if not better than, us (note also the punctuation).