246 OLIVE OILS AND HEALTH - controlled; controlled study A clinical trial in which two groups are compared, one of them being the reference group (control group). - crossover A type of clinical trial in which all participants receive the same two or more treatments sequentially, but the order in which they receive them depends on the group to which they are randomly assigned. - survival curves Lines or curves plotted on a graph indicating the survival rates of a specific population during all the steps throughout the study follow-up period. - double blind Clinical trial in which neither the participants nor the researcher who evaluates the outcomes (events or end-points) know which treatment or intervention each participant is receiving. The objective is to avoid bias (i.e., subjective adjudication of outcomes, whether conscious or unconscious, by participants or researchers). - randomised trials; randomised study/ies; randomised controlled trials Human prospective experimental studies in which researchers randomly assign each participant to a treatment group or a control (or comparator) group. - intervention studies; randomised intervention studies (or trials); intervention studies; intervention; short-term intervention; dietary intervention; nutritional intervention Human analytical prospective studies in which participants are assigned, not always randomly, to a treatment (e.g., a diet or drug) or a control group (or comparator) group. · short-term intervention Studies in which recommendations are followed or treatments are administered for less than three months. · nutritional intervention Studies in which dietary recommendations, treatments, or supplements are administered to participants. - observational prospective studies (or trials); cohort; observational cohort; prospective cohort studies; observational studies; prospective • Non-experimental human epidemiological studies in which researchers follow and observe a group of subjects over time according to their exposure status. The goal is to gather information and compare groups with different exposures (protective or risk factors). Participants are usually disease-free at baseline. The follow-up typically spans several years to assess the incidence of new cases according to exposure levels at the start. These are also known as cohort studies. Although they can be retrospective, they are usually prospective. - ecological studies They form part of the epidemiological descriptive observational designs. They compare large population groups instead of individuals. The unit of analysis is the group, not the individual. These groups can differ in characteristics (e.g., countries, provinces, schools). An example would be to compare the incidence of a disease among countries. Ecological studies are usually only descriptive and of historical temporality, but they can also be useful
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