Thanks @Evan_Minty , this is a PHreaking PHenomenal PHenotype clinical description. I learned a lot about PH reading this. One of the things that struck me in reading this is that diagnostic procedures are necessary to produce a proper diagnosis, and yet are not always performed. If I’ve got that right, then it means there’ll be a pretty big difference between ‘biologically true’ PH and ‘clinically recognized’ PH. It also suggests there could be substantial misclassification between the PH groups without sufficient measurements. I know @Eva-M and @jswerdel have dug into this for PAH, and I’m keen to see how their work stacks up with other publications and other approaches you come up with.