When a researcher assigns participants to either an experimental or a control group based on their last names, systematic differences between groups are created before the experiment even begins. This is a confounding variable referred to as Group of answer choices

"Selection bias " is the correct answer.

Explanation:

Selection bias seems to be a statistical prejudice from which a mistake arises in determining the individuals to participate throughout a research sample. The selection effect has often been started referring to each other like this.The significant problem would be that personal-selection seems to be a particular activity that can overlap with certain similar behaviors and this study sometimes doesn't represent the overall population.

Absolute !

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