The Supreme Court Friday refused to lay down a yardstick for granting reservation in promotion to Scheduled Castes and Scheduled Tribes in government jobs. A three-judge bench headed by Justice Nageswara Rao said states are obligated to collect data on inadequacy of representation of SCs/STs. The apex court said it cannot lay down any yardstick to determine the inadequacy of representation of SCs/STs and it for the states to do so.