Mark has a hypothesis that darkness makes people more aggressive. To test this, he brings participants into the lab. The first 10 participants who come to the lab are put into a dark room with no lights. The next 10 participants who come to the lab are put into a fully lit room. He then measures how hard they hit a punching bag.

What is one problem with Mark's experiment?

A. It lacks an independent variable.
B. It lacks random assignment.
C. It lacks a manipulation.
D. It lacks a dependent variable.

One problem with Mark's experiment is that it lacks random assignment. Random assignment is crucial in experiments to ensure that each participant has an equal chance of being in either the experimental or control group, reducing bias and increasing the validity of the results.

For example, in Mark's case, if participants who are more naturally aggressive tend to come in first, they may all end up in the dark room, skewing the results. Random assignment helps distribute individual differences evenly between groups.

Without random assignment, the results may not accurately reflect the effect of darkness on aggression, as other variables could be influencing the outcome.

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