A researcher is studying the effect of soothing music on people's anxiety while having their teeth cleaned at the dentist. A group of volunteers is randomly assigned into two groups. One group is exposed to soothing music while having their teeth cleaned, and the other group is not exposed to any music. The researcher measures the anxiety levels of both groups before and after the teeth cleaning procedure. What is the purpose of randomly assigning the volunteers into two groups?
1) To ensure that both groups have similar anxiety levels before the teeth cleaning procedure
2) To determine the effect of soothing music on anxiety levels during teeth cleaning
3) To compare the anxiety levels of the two groups after the teeth cleaning procedure
4) To eliminate any bias or confounding factors that could affect the results