the studies do not rank in the hierarchy of clinical trial data , they are not often considered to influence clinical care and they may be considered merely ' descriptive ' of a medical problem . despite the limitations of epidemiology studies , they remain a critical component of biomedical research without which the remaining ' higher order ' studies , such as cohort studies and controlled trials , could not be effectively conducted . critical care epidemiology studies , of which the current study from the intensive care national audit and research center database is a good example , serve a variety of purposes that advance the mission of both practicing intensive care unit ( icu ) physicians and scientific researchers . at the most basic level , epidemiology studies convey important information about disease characteristics , the type of patients affected , and the frequency and outcomes of the disease . epidemiology studies report and reinforce the frequency of deaths related to atherosclerotic disease , cancer and sepsis in developed countries , and of deaths from a variety of infectious diseases and sepsis in developing countries . these reminders are essential in an era of increasing media attention on diseases such as severe acute respiratory syndrome and avian influenza that are less immediate public health concerns . descriptive epidemiology studies also inform intensivists about the type of conditions they should expect to encounter in their icu ( i.e. the frequency of disease ) and they guide clinicians in treating patients by reporting information on relative causality ( such as streptococcus pneumoniae being the most common cause of community - acquired pneumonia ) . local and regional epidemiology data have long been disseminated to tailor therapy for infectious diseases based on local organism resistance patterns . in contrast , larger epidemiology studies are invaluable for determining healthcare resource allocation and for the design and conduct of both observational and interventional clinical trials . longitudinal studies add a vitally important characteristic to point - prevalence or time - limited epidemiology studies . they permit characterization of temporal changes in affected patients and in disease characteristics , such as in the frequency , complications and outcomes of a disease . longitudinal studies also permit more detailed planning for healthcare resource allocation , in particular by matching temporal changes in disease or disease - specific outcomes with known changes in underlying patient populations ( e.g. hiv - positive ) or according to rendered treatments ( e.g. antibiotics , chemotherapeutics ) . longitudinal epidemiology studies on a local level can be utilized for quality control purposes , to assess the impact of changes in healthcare delivery . in general , longitudinal studies are invaluable for understanding how a disease is changing and how it affects patients in the studied healthcare system . epidemiology studies that cross physical and geopolitical borders permit broader comparisons than would be possible for observations that are geographically constrained . most simply , they allow comparisons to be drawn for diseases according to different pressures , such as differing underlying patient populations and different risk factors for disease . more broadly , when epidemiology studies are conducted they longitudinally create the ability to examine healthcare quality and effectiveness of resource utilization on a regional scale or a national scale in relation to scientific advances . data of this kind are essential for determining the optimal icu utilization for a given condition , tracking the effectiveness and efficiency of healthcare systems according to changes in disease incidence or outcome , and for planning research studies according to the characteristics of the disease . in the present issue of critical care , investigators from the intensive care national audit and research center report the results of a longitudinal study of severe sepsis encompassing england , wales and northern ireland in the past 10 years . these data are indispensable as a baseline assessment for a common and lethal condition in the respective countries , where severe sepsis occupies more than one - quarter of icu beds and carries fatality rates approaching 50% . the data confirm previous secular trends in the incidence and mortality of sepsis [ 2 - 4 ] and define the severity of disease and heterogeneity of case - mix typical of sepsis . with these data in hand , scientists and healthcare administrators may assess the impact of community interventions designed to reduce the incidence of sepsis or medical therapies that may improve outcomes with sepsis . the value of these data is even more apparent in a system of national healthcare insurance , where tracking of health - related outcomes related to resource allocation is necessary to ensure appropriate healthcare delivery . other large - scale epidemiology studies exist for sepsis , either by sampling locally ,   regionally [ 3,6 - 9 ] , nationally [ 4,10 - 15 ] or internationally . few available studies cross systems of care or permit direct comparisons of healthcare delivery strategies . those studies that include longitudinal data provide important additional insights into sepsis epidemiology while minimizing seasonal influences . continued investigation is necessary to optimize healthcare quality and to compare the effectiveness and efficiency of different icu utilization and care strategies , both nationally and internationally .
epidemiology studies are an essential part of clinical research , often forming the foundation for studies ranked more highly in the hierarchy of evidence - based medicine 
 . studies of sepsis to date have been conducted on local , regional , national and international scales , with the majority conducted in the past 5 years . 
 longitudinal epidemiology studies convey an important additional aspect of the healthcare burden from disease , and may additionally serve to compare the effectiveness and efficiency of healthcare systems , to examine specific patient care strategies and to perform quality control analyses .