A researcher selects a sample of female teachers and assigns half the teachers to one professional development group and the other half of teachers to a different professional development, such that...

A researcher selects a sample of female teachers and assigns half the teachers to one professional development group and the other half of teachers to a different professional development, such that all teachers have an equal probability of being selected to one or the other group. What type of procedure was used to assign teachers to groups in this example?