probability is very low, it is not logical to assume that it is actually zero. The definition of quantum correlation is adapted to the idea that outcomes will always be +1, −1 or 0. There is no obvious way of including any other possibility, which is one of the reasons why Clauser and Horne's 1974 Bell test, using single-channel polarisers, should be used instead of the CHSH Bell test. The CH74 inequality concerns just probabilities of detection, not quantum correlations. Quantum states with a local hidden-variable model For separable states of two particles, there is a simple hidden-variable model for any measurements on the two parties. Surprisingly, there are also entangled states for which all von Neumann measurements can be described by a hidden-variable model. Such states are entangled, but do not violate any Bell inequality. The so-called Werner states are a single-parameter family of states that are invariant under any transformation of the type where is a unitary matrix. For two qubits, they are noisy singlets given as where the singlet is defined as . R. F. Werner showed that such states allow for a hidden-variable model for , while they are entangled if . The bound for hidden-variable models could be improved until . Hidden-variable models have been constructed for Werner states even if POVM measurements are allowed, not only von Neumann measurements. Hidden variable models were also constructed to noisy maximally entangled states, and even extended to arbitrary pure states mixed with white noise. Beside bipartite systems, there are also results for the multipartite case. A hidden-variable model for any von Neumann measurements at the parties has been presented for a three-qubit quantum state. Generalizations of the models By varying the assumed probability and density functions in equation (), we can arrive at a considerable variety of local-realist predictions. Time effects Previously some new hypotheses were conjectured concerning the role of time in constructing hidden-variables theory. One approach was suggested by K. Hess and W. Philipp and relies upon possible consequences of time dependencies of hidden variables; this hypothesis has been criticized by R. D. Gill, G. Weihs, A. Zeilinger and M. Żukowski, as well as D. M. Appleby. Optical models deviating from Malus's law If we make realistic (wave-based) assumptions regarding the behaviour of light on encountering polarisers and photodetectors, we find that we are not compelled to accept that the probability of detection will reflect