In psychology lab, Tetiana is conducting an experiment on depth perception using the Howard-Dolman box. Inside the box are two vertical rods and a horizontal ruler. The participant manipulates the rods until they appear to be aligned at the same distance away, then the experimenter measures how far out of alignment they are. There are three conditions: left eye only, right eye only, and both eyes. Tetiana is using a repeated-measures design. How is the independent variable being manipulated in Tetiana's design?

According to my research on the scientific method, I can say that based on the information provided within the question the independent variable is being manipulated within groups, because she is not using a pretest and her design is within-groups. This is because she is using the posttest-only control group design which is a research design where at least two groups, one of which does not receive a treatment or intervention, and data is collected on the outcome measure after the treatment or intervention.

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