Poor Study Design: Inadequate randomization, improper control selection, or inappropriate sampling methods can lead to bias. Measurement Errors: Inaccurate tools or inconsistent methods in data collection can introduce bias. Loss to Follow-up: When participants drop out of a longitudinal study, the remaining sample may not be representative of the original cohort. Uncontrolled Confounders: Not accounting for potential confounding variables can distort the true association between exposure and outcome.
