The following table summarizes COPCs symptoms, U.S. prevalence estimates and the age range when these conditions typically begin. Large, national, multi-site studies on people with two or more of these conditions are underway and will soon begin yielding high-quality data on the prevalence rates of co-occurrence, their temporal relationship (i.e., which conditions are more likely to come before or after other conditions), and age ranges when overlap of these conditions are most likely to occur.