At the end of the study the investigator analyzes the incidence of the outcome in the group of exposed and non-exposed to the risk factor (s) in a contingency table ( Table 1). In the case of the retrospective study the researcher can collect previous information on the exposure factor (s) (hence the retrospective term) and accompany individuals for a period of time (the cohort).Īfter some time of monitoring (months, years or decades) the researcher can relate the exposure to the outcome(s) using the Relative Risk (RR), which is nothing more than the incidence of the outcome (s) in the cohort. In the prospective study the researcher is present at the time of exposure of one or more factors and accompanies for a period of time to observe one or more outcomes. Roughly this study can be divided into 2 subtypes: a retrospective cohort study and a prospective cohort study ( Figure 1). These studies (also called longitudinal or "follow-up") assume that the researcher will follow a population over time to seek a possible (at least statistical) association between exposure and outcome. While observational studies raise more hypothesis rather than showing causal association, experimental studies, considered the gold standard of epidemiological studies, are expensive, time-consuming but more accurate and may show a causal relationship between exposure and outcome. They all have different advantages, disadvantages, costs, runtime and accuracy.
These (analytical) studies, on other hand, are divided into observational (cross-sectional study 4, case-control study and cohort study) and experimental studies, best known as clinical trials 1-3. The second part, on other hand, uses data from descriptive epidemiology to analyze and seek explanations and/or associations for the descriptive data 1-3. In the first part, indicators of morbidity, mortality, demographic, socioeconomic, quality of access health services and quality of life are used, among others.
The epidemiological method, in the area of Health Sciences, can be divided into two main areas: descriptive and analytical epidemiology. That the cohort study, even with some biases, is a method that can estimate the incidence of an outcome (or more) exposed to one or more factors, and verifies whether there is a statistical association between exposure and outcome, either primary and secondary. In the prospective study, the researcher is present at the exposure of one or more factors and followed for a period of time to observe one or more outcomes. In the retrospective study the researcher collects previous information on exposure factors and over time the in individuals.
It was found that the cohort study may be retrospective and prospective. The present study was conducted to show the advantages and biases of a prospective and retrospective cohort study, demonstrating its application and in which situations it is indicated. Keywords: cohort, longitudinal study, follow-up. These are studies that may point to statistical associations between exposure and outcome that need other models to prove the casualty of these associations. They have as main biases those of selection, memory and information. However, they are often long and therefore expensive studies. These types of studies have as advantages the possibility of measuring several exposure factors and outcomes, both primary and secondary, for both relatively frequent outcomes and rare exposure factors. Cohort studies may be retrospective or prospective, and both assume that the researcher will follow a population over time to seek a possible association between exposure (s) and outcome(s). In health sciences, the epidemiological method can be divided into descriptive and analytical epidemiology and the latter being divided into observational (cross-sectional study, case-control study and cohort study) and experimental studies. VIISchool of Application, Federal University of Acre, Rio Branco, Acre, Brazil VICenter for Health and Sports Sciences, Federal University of Acre, Rio Branco, Acre, Brazil VStricto Sensu Graduate Program in Health Science in the Western Amazon, Federal University of Acre, Rio Branco, Acre, Brazil IVNational Institute of Science and Technology EpiAmo / Rondônia IIICenter of Tropical Medicine of Rondônia, Porto Velho, Rondônia, Brazil IIDepartment of Medicine, São Lucas University Center, Porto Velho, Rondônia, Brazil IInstitute of Biomedical Sciences, University of São Paulo, Monte Negro, Rondônia, Brazil Luís Marcelo Aranha Camargo I, II, III, IV, V Romeu Paulo Martins Silva V, VI Dionatas Ulises de Oliveira Meneguetti V, VII Research methodology topics: Cohort studies or prospective and retrospective cohort studies
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