A researcher has manipulated only one independent variable at two levels,has held constant as many other variables as possible and has balanced individual differences by using random assignment.The researcher is likely to be able to claim that the independent variable caused the observed changes in the dependent variable because the experiment is

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By manipulating only one independent variable at two levels, holding constant as many other variables as possible, and balancing individual differences by using random assignment, the researcher has ensured that the experiment is internally valid. This means that the observed changes in the dependent variable are likely to be caused by the manipulated independent variable, rather than by other factors.

A Researcher Has Manipulated Only One Independent Variable at Two