Unintended differences between the groups in an experiment reflect bias; these differences stem from a failure to follow the principle of random .

A systematic investigation and analysis of the known knowledge and data to establish new facts and discoveries is called research.

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When the researchers decide the participants then the result for the sample will be biased and not truly correct.

It gives a fair opportunity for the selected participants in the research.

To learn more about selection bias and random assignment follow the link:

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Selection; assignment.

Explanation:

Selection bias can be defined as a bias in research when the selection of participants is not random. This creates problems in obtaining the sample. This bias occurs when participants, that is, people who are going to be studied, are decided by the researcher.

Random assignment is the selection process in research. This process ensures equal opportunities for the participants and help eliminate any kind of bias. The violation of this process leads to the selection bias discussed above.

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answer; role-taking;