AQA Psychology – Research Methods Practice Test

Controlling extraneous variables keeps everything other than the manipulated factor the same across conditions. If these unwanted factors creep in, they can influence the dependent variable, making it unclear whether any observed effect comes from the independent variable or from those other factors. By standardizing procedures, randomizing participants, and keeping the environment consistent, you reduce alternative explanations and strengthen internal validity. In that sense, the observed change in the dependent variable is more likely due to the independent variable you manipulated. The other options don’t address this issue—increasing sample size, debriefing, or speeding up data collection don’t ensure that changes in the outcome are caused by the manipulation itself.