sentences:  This has been attributed to more thorough entry-level and continued training, better supervision and operational procedures and medical and fitness screening.In the United States scientific diving is done by research institutions, universities, museums, aquaria, and consulting companies for purposes of research, education and environmental monitoring.As of 2005 there were an estimated 4000 scientific divers, of which a small number are career scientific divers, with an average age of around 40 years, and a larger number of students in the 18 to 34 year age group.