Hello, my name is Andreina Fernández and I am a molecular biologist from Caracas, Venezuela, and today we will be discussing the observational studies. I declare that I have no conflict of interest for this talk. Well, these are the topics that we will be discussing during the presentation. We will be talking about characteristics, strengths and weaknesses of the observational studies, the common problems and errors, common analysis and interpretation tools, scope and limitations of the observational studies, and finally, tools for critical reading. Observational studies are those where the investigator is not acting upon study participants, but instead is observing natural relationships between factors and outcomes. We can evaluate risk factors, diagnostic tests and treatments. But sometimes observational studies are the only way researchers can explore certain questions. For example, we can have unethical situations. Although randomized clinical trials are very effective in producing quality scientific evidence, we cannot always use them. For example, we can design a randomized control trial for deliberately exposing workers to a potentially harmful situation. Another example are the rare conditions. Observational studies may be the most efficient way to identify potential costs or to identify how a problem develops over time. How can we classify observational studies? We have two groups based on the number of times we evaluate a population. If we measure once and we don't have a comparison group, we are talking about descriptive studies. We have ecological studies and case reports and case series. If we measure more than once, we have longitudinal studies, and with a comparison group, we are talking about analytical studies. Case control studies represent the retrospective studies, and the cohort studies and systematic review represent the prospective studies. Now we must define the retrospective and prospective studies. In retrospective studies, we look back. These types of studies cannot demonstrate temporality as easily and are more prone to different biases. In prospective studies, we look forward. These types of studies are less prone to some types of biases and can more easily demonstrate that the exposure precedes the disease. Now let's talk briefly about the types of observational studies. We start with case reports and case series. These are detailed reports of the symptoms, signs, diagnosis, treatment, and follow-up of a case, usually describe an unusual or novel occurrence, and as such remain one of the cornerstones of medical progress and provide many new ideas in medicine. In general, case reports imply one case, and case series could be more than two or more than ten cases. Cross-sectional studies are primarily used to determine prevalence. The prevalence equals the number of cases in a population at a given point in time. So all the measurements on each person are made at one point in time, a difference to case control studies or prospective studies that the measurements are made more than one time. The cross-sectional studies do not involve manipulating variables, consider several characteristics at once, analyze the prevailing characteristics in a given population relatively quickly, and generate hypotheses. Now the case control studies are usually retrospective. People with the outcome of interest, that is the cases, are matched with the control group who do not. The researcher determines which individuals were exposed to the agent or treatment or the prevalence of a variable in each of the study groups. These types of studies are useful for hypothesis generation, can only look at one outcome, but the bias is a major problem due to the selection cases. Therefore, the cases should be selected based on a definition of inclusion-exclusion criteria and control selection should be subject similar to the cases but without the disease. The cohort study involves identifying study participants based on their exposure status. We can follow the participants through time to identify which of them developed the outcome of interest or we can look back at the data that were created in the past prior to the development of the outcome. With this type of study we can describe incidents or natural history. In cohort studies we select two types of individuals. One group of exposed individuals to some conditions and a second group of unexposed individuals. In cohort studies we have two types of studies. Prospective cohort studies in which, over a period of time, the people in the sample are observed to see whether they developed the outcome of interest and retrospective cohort study and in this case the cohort is followed retrospectively. The study period may be many years but the time to complete the study is only as long as it takes to collate and analyze the data. What are the common errors associated to observational studies? First, we have bias. The inclusion of subjects or methods such that the results obtained are not truly representative of the population from which it is drawn and second, the confounding variables. There is a variable associated with both the exposure and outcome of interest that is not the variable being studied. We have scope and limitations and regardless to scope of observational studies we can evaluate treatment and diagnosis, we can evaluate prevention and natural history and the etiology of some disease, but we also can evaluate unusual manifestations and rare disease, but we have also some limitations related to personal subjectivity, reporting biases, sometimes the cost associated to the designs of some types of observational studies, the absence of comparisons between groups and finally limited experience of a research group. Finally, we have an important tool for the critical reading of observational studies. This is the STROB guidelines. STROB means strengthening the reporting of observational studies in epidemiology. This is an internationally collaborative initiative of epidemiologists, methodologists, aestheticians, researchers and journal editors involved in the conduct and dissemination of observational studies and this is the website of these guidelines. The guidelines consist of a checklist of 22 items which relate to title, abstract, introduction, methods, results and discussion. Of these 22 items, 18 are common to cohort studies, case control studies and cross-sectional studies and four of these are specific to each of the three study designs. In general, the STROB statement provides guidance to authors about how to improve the reporting of observational studies and facilitates critical appraisal and interpretation of studies by reviewers, journal editors and readers. This is an example of the checklist of the STROB guidelines. You can see that we have an item for title and abstract, we have an item for introduction, for the method section which includes study design, setting, participants, variables, data source, measurement, bias, study size, quantitative variables and statistical methods. Also, we have some items for results which include participants, descriptive data, outcome data, main results and other analysis and finally we have the items for discussions which include key results, limitation and interpretation and other information such as funding associated with the design of the study. In conclusion, we can say that qualitative studies can produce high-quality information but all such studies can be influenced by known and unknown confounding variables. Appropriate use of observational study permits investigation of prevalence, incidence, association, cause and outcome. Where there is little evidence on a subject, there are cost-effective ways of producing and investigating hypotheses before larger and more expansive study designs are embarked upon. And finally, they are often the only realistic choice of research methodology particularly where a randomized controlled trial would be impractical or unethical. Well, thank you for your attention during this presentation.

observational studies

risk factors

diagnostic tests

treatments

STROBE guidelines