Which of the following is not a factor involved in the process of evaluating an observational study?

Introduction

Results

Discussion

Bias

Results and Discussion are definitely very relevant for examining an observational study - they contain the core of the study, so they will definitely be considered when evaluated.

So we choose between "Bias" and "Introduction".

I think that the correct answer is "Introduction" - as it doesn't include any new information about the study, and only summarizes previous work.