Answer:
Experiments: Experiments are controlled investigations designed to explore the cause-and-effect relationships between variables. In an experiment, researchers manipulate one or more independent variables to observe the effect on a dependent variable while keeping other factors constant. This allows them to draw conclusions about the impact of the manipulated variables on the outcome of interest.
Observational study: An observational study is a type of research design in which researchers observe and collect data on individuals or groups without directly intervening or manipulating any variables. The goal is to understand relationships or associations between variables as they naturally occur in the population. Observational studies do not involve any intentional intervention or treatment assignment.
Experimental units: Experimental units are the subjects or entities on which the experiment is conducted. They can be individuals, animals, plants, organizations, or any other units that are the focus of the study. In a medical context, patients might be the experimental units, while in an agricultural study, experimental units could be plots of land.
Retrospective study: A retrospective study is a type of observational study where researchers analyze existing data or records from the past to investigate relationships between variables. The data is already available, and researchers do not have control over how it was collected. Examples of retrospective studies include examining medical records to study the effects of a treatment on patient outcomes.
Treatment: In the context of experiments, a treatment refers to the manipulation or intervention applied to the experimental units by the researchers. It is the specific condition or set of conditions that the subjects are exposed to. The goal of an experiment is often to compare the effects of different treatments to assess their impact on the dependent variable.