A research team aims to evaluate the effectiveness of a new online tutoring program for college students. They recruit participants by sending an email invitation to all students enrolled in introductory psychology courses, offering extra credit for participation. Which of the following biases is most likely to affect the study's internal validity due to this sampling method?
Show answer and explanation
The answer
Correct answer: D. The study will likely suffer from self-selection bias, as students who choose to participate may differ systematically from others.
Tested concept: Sampling methods and bias
Explanation
The sampling method described involves inviting students who then choose whether or not to participate. This creates a self-selection bias (also known as volunteer bias), where the characteristics of those who opt-in (e.g., motivation, academic struggle, interest in extra credit) may systematically differ from those who do not. This difference can confound the results, making it difficult to attribute any observed effects solely to the tutoring program, thus threatening internal validity. Observer bias relates to researchers' expectations influencing results, response bias relates to participants' answers on measures, and confirmation bias relates to researchers' interpretation of data, none of which directly stem from the initial participant recruitment method in this specific way.
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