Prospective cohort studies epidemiological study designs

EXPOSURES RELEVANT TO HEALTH THE CONCEPTUAL FRAMEWORK 246 Considerations of Exposure Timing 246 Considerations of Exposure Route 247 Practical Context of Pesticide Exposure 248 EPIDEMIOLOGICAL STUDY DESIGNS AND EXPOSURE ASSESSMENT 248 Prospective Cohort Studies 248 Retrospective Cohort Studies 249 Case-Control Studies 250 Cross-Sectional Studies 252 EXPOSURE ASSESSMENT STRATEGIES 252 INFLUENCE OF THE ACCURACY OF EXPOSURE PROXIES ON MEASURES OF ASSOCIATION 254 Errors in Qualitative Proxies 254... 

Epidemiological evidence of the overall association between analgesic abuse and the development of renal impairment is documented in nine case-control studies [16-18, 20-21,33-34, 36-38], two prospective cohort studies [39, 40] and two observational cohort studies [41, 42] published in the last decades (Figure 1). It is inherent to epidemiological studies however, that the observed association between chronic renal failure and analgesic consumption does not establish cause and effect. Moreover, serious flaws in study design and analysis of the data have to be considered and were discussed in several reviews (Table 1) [7, 43,44,45]. 

Epidemiological studies have different strengths and weaknesses associated with their design (Table 4) shows some of the strengths and weaknesses of the two main methods of prospective cohort studies and retrospective case-control studies. 

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. 

To compare the epidemiological, clinical, and economic impacts of the HIV epidemic in Italy prior to and after the introduction of HAART, Tramarin et al. (2004) conducted a prospective and observational study with a multi-center design. They used data collected on an AIDS cohort from 1994 and updated data from a comparable cohort in 1998. Mortality and medical costs of 251 patients were measured in 1994 and in 1998, respectively. A considerable difference was observed in mortality (33.9% in 1994 vs. 3.9% in 1998). The cost per patient per year was US 15,515 in 1994 and US 10,312 in 1998. Based on the comparison of the two cohorts between both years, the authors concluded that after the introduction of HAART, hospital-based provision shifted from an inpatient-based to an outpatient-based service, with major focus on pharmaceutical care. 

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