Aresearch design involves two randomly assigned groups of participants. one group receives a one-time treatment, and the other does not. later, the two groups are compared to see whether the treatment had an effect. psychologists call this kind of research

The correct answer is: An experiment.

Explanation:

An experiment can be defined as a study that tries to prove or disprove a certain hypothesis.

Experiments usually involve at least one independent variable that is manipulated to see how it affects the dependent variable.

The independent variable is believed by the researches to have an effect in the dependent variable, the experiment is conducted to prove this.

In this particular case, the research consists of two randomly assigned groups of participants. In the study one group receives a one-time treatment (Which in this case this is called the Independent variable) and the other does not.

Later, the two groups are compared to see whether the treatment had an effect. (Dependent Variable)

In conclusion, this type of research design is called: An Experiment.