  This paper is concerned with quasi-unbiased Hadamard matrices and weakly
unbiased Hadamard matrices, which are generalizations of unbiased Hadamard
matrices, equivalently unbiased bases. These matrices are studied from the
viewpoint of coding theory. As a consequence of a coding-theoretic approach, we
provide upper bounds on the number of mutually quasi-unbiased Hadamard
matrices. We give classifications of a certain class of self-complementary
codes for modest lengths. These codes give quasi-unbiased Hadamard matrices and
weakly unbiased Hadamard matrices. Some modification of the notion of weakly
unbiased Hadamard matrices is also provided.
