The National Academies of Sciences, Engineering, and Medicine are private, nonprofit institutions that provide expert advice on some of the most pressing challenges facing the nation and world. Our ...

A class of semi-Markov models, those which have proportional hazards and which are forward-going (if state j can be reached from i, then i cannot be reached from j), are shown to fit into the ...

Science Scope is an award-winning, peer-reviewed, practitioners' journal for grade 6–8 teachers, university faculty responsible for teacher preparation, and state and district science supervisors and ...