Question: A cohort study is conducted to compare the incidence of adverse effects of a recently approved antihypertensive pharmacotherapy with that of conventional therapy. A total of 20,000 patients are enrolled. Twelve thousand are prescribed the recently approved therapy, and 8,000 are prescribed conventional therapy. Patients in the study and control groups are matched for baseline blood pressure, age, and gender. Data are collected from the records of the patients' ongoing clinical care. Results show that those receiving the newly approved treatment have twice the incidence of fatigue compared with those receiving the conventional treatment. The results are statistically significant (p=0.01). Which of the following potential flaws is most likely to invalidate this study?
A: Publication bias
B: Selection bias
C: Type I error
D: Type II error
Please eliminate two incorrect options first, then think it step by step and choose the most proper one option. Write exactly 4 paragraphs each separated with two new lines answering this question. The first paragraph must start with "overall".
user