In this paper, the effect of absolute values on the behavior of functions f in the spaces, but the converse is not always true. For f in the Hardy space H 2 , we give a condition involving the modulus of the function only, such that this condition together with |f | ∈ Q K (∂D) is equivalent to f ∈ Q K . As an application, a new criterion for inner-outer factorisation of Q K spaces is given. These results are also new for Q p spaces.