Similar to other types of research, study designs used in IR can be interventional or observational. In an interventional research design, the researcher influences objects or situations and then measures the outcome of these manipulations. In an observational study design, the researcher observes and analyses researchable objects or situations without intervening. These non-intervention studies can be exploratory, descriptive and comparative (analytical) studies, while intervention studies can be experimental studies, quasi-experimental, before and after, cohort studies or randomized controlled trials. Below each of these study designs is briefly explained.