Trials and observational studies are methods that researchers can use to evaluate the impact of treatments and interventions. Trials use an experimental design to test treatments or interventions on a group of participants, while observational studies involve watching how participants react to something, such as a treatment, but do not involve controlling which participants receive treatments. Trials can be called clinical trials or randomised controlled trials, and examples of observational studies include case-control studies, cross-sectional studies, cohort studies and natural experiments. Natural experiments are when researchers evaluate the impact of changes that are happening anyway (for example, if a new road is being built through an urban area, a natural experiment might investigate how the road affects local people's health).
Sometimes research papers describe pilot studies (or feasibility studies), which are early studies carried out to test the methods that might be used in a larger trial or observational study.
Read the abstract and introduction of the study that you are interested in. Do you think the research is a trial, an observational study or a pilot study?
Understanding Health Research