Psychiatric epidemiology is a field which seeks to study the conceptualization, etiology, and prevalence of mental illness in society. It is a subfield of the more general epidemiology. It is very difficult to accurately study mental illness conceptualization, etiology, and prevalence, and current techniques are relatively poor. Two areas of concern, sometimes called the crisis of psychiatric epidemiology today, are the high estimates of mental illness that many studies produce and the difference in results between studies.