The present disclosure relates to apparatus (1) for estimating confidence in a vehicle reference velocity (V). The apparatus includes a controller having an electronic processor (21) having an electrical input for receiving at least one first vehicle operating parameter; and an electronic memory device (23) electrically coupled to the electronic processor and having instructions stored therein. The electronic processor (21) is configured to access the memory device (23) and execute the instructions stored therein such that it is operable to monitor the at least one first vehicle operating parameter; and to calculate a confidence value (F1) representing the confidence in the vehicle reference velocity, the confidence value (F1) being calculated in dependence on the vehicle operating parameter.