Prospective cohort studies defined

An alternative to the prospective cohort study is the retrospective cohort study, in which a defined population with a past exposure has an existing measurable health outcome. The past exposure needs to be well documented so that a given level of exposure can be assigned to each individual in the population. 

Although, in general, prospective cohort studies of well-defined groups of patients are superior, retrospective studies may have the advantage of longer follow-up, which might be necessary for a clinically relevant prognosis or simply in order to have a sufficient number of outcome events to construct a reasonably precise prediction model. However,... 

Prospective cohort study A study in which subsets of a defined population who are, have been, or in the future, may be exposed and unexposed individuals are selected and followed concurrently over time to determine whether or not they develop the disease(s) of interest and with what frequency (Heederik and Teschke, Ch. 7). 

Prospective Cohort Study Prospective cohort studies are no different in principle from historical cohort studies in terms of scientific logic, the major differences being timing and methodology. The study starts with a group of apparently healthy individuals whose health and exposure are studied over a period of time. As it is possible to define in advance the information that is to be collected, prospective studies are theoretically more reliable than retrospective studies. However, long periods of observation may be required to obtain results. 

A series of clinical outcome reports have demonstrated that measures of PD solute removal correlate with patient status and outcome. In particular, a multicenter prospective cohort study of 680 incident CAPD patients [Canada-United States (CANUSA) Study] showed that a decrease of 0.1 in weekly urea clearance (defined by Kt/V ,ea) was associated with a 5% increase in the relative risk of death. Similarly a decrease of 5L/wk/1.73m of total creatinine clearance (Cc,) was associated with a 7% increase in the risk for death. As a consequence of these studies, national guidefines from the United Kingdom, Australia, and the United States " have set standards of dialysis adequacy in terms of small solute removal. An estimate of adequacy is performed in all patients withm 6 to 8 weeks of commencement of dialysis. Further studies should be performed at least annually. ... 

Field, D.J., et al., 2008. Survival of extremely premature babies in a geographically defined population prospective cohort study of 1994—1999 compared with 2000—2005. BMJ (Clinical Research Ed.) 336 (7655), 1221—1223. Available at http //www.pubmedcentral. ruh.gov/articlerender.fcgi artid=2405852 tool=pmcentrez renderlype=abstract (accessed... 

Legend Hcoh Historical cohort study Pcoh Prospective cohort study RCT Randomized controlled trial Average mobility was calculated from the reported data [25] Overall clinical success was defined as patients having >25% improvement in ODI score at 24 months compared with the preoperative score, no device failure, no major complications, and no neurological deterioration [26], Five-year followup of this series have been reported in conference presentations [15], but these results have not yet appeared in the peer-reviewed literature. 

Legend Hcoh Historical cohort study Pcoh Prospective cohort study RCT Randomized controlled trial Overall clinical success was defined by FDA as patients having achieved >15% improvement in ODI, SF-36, mdiogmphic success, and neurologic success, all without device failure [42]. 

An epidemiological study in which a defined group of persons known to be exposed to a potential disease risk factor is followed over time and compared to a group of persons who were not known to be exposed to the potential risk factor to evaluate the differenees in rates of the outcome. Also termed a prospective study, followup study, incidence study, retrospective cohort, or historical cohort study. 

Prospective study. A rather loose term which may, perhaps, be defined as a study in which the measurement of the presumed causal factors is both temporally and logically prior to the measurement of the outcomes of interest (the presumed effect )- In this sense the term applies to clinical trials and also to many cohort studies. 

A variety of biomarkers have been shown to be valuable individually for one or several toxicant or disease situations. Few of these biomarkers have been systematically evaluated for the plethora of situations that might provoke false positive responses. Acceleration of the current pace of biomarker evaluation and qualification demands (a) the availability of panels of biomarker-assays that can be comparatively evaluated on well-defined common sample sets, (b) fit-for-purpose performance evaluation in controlled animal studies with carefully benchmarked histological endpoints and samples from well-defined focused clinical trial cohorts, and (c) ready availability of banked blood and urine sample archives from clinical trial populations with carefully documented morbidities such as the Framingham Heart Study,45 or the Drug-Induced Liver Injury Network (DILIN) prospective study,46 to name a few. Availability of such panels of validated biomarker assays and well-documented preclinical and clinical samples, as well as increased cooperation between animal model researchers and clinical researchers will enable individual biomarkers to be qualified for sensitivity of specifically defined adverse events, qualified for appropriate specificity using samples of defined benign events, and collected into panels that yield complementary information about the health and safety of animals and patients. 

Nested case-control study A type of epidemiological research design which investigates the causal association between a risk factor and disease. Both case subjects (people who develop a disease) and control subjects (those who do not develop the disease) are selected from among a defined cohort in which the bio-sample or data of the individuals have been collected at the beginning of the study. Detailed exposure information, such as via the use of biomarkers, is analysed for cases and controls only, not for the entire cohort. The advantages of this design are that it is prospective and is less expensive than the full cohort approach. 

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