Which statement correctly contrasts random variation with systematic variation?

• A. Random variation results from chance; systematic bias is constant and needs correction.
• B. Random variation is always biased.
• C. Systematic variation arises from random sampling.
• D. All variation is random and cannot be corrected.

Answer: (A)

Variation in data comes from two distinct sources: random variation, which arises by chance and tends to fluctuate around the true value, and systematic variation (bias), which pushes measurements in a consistent direction and does not disappear with more data. The statement that best captures the contrast says random variation results from chance, while systematic bias is a constant distortion that needs correction. This fits how sampling and measurement error introduce unpredictable fluctuations that can be reduced by larger samples or better methods, whereas bias remains and must be addressed through study design, calibration, or statistical adjustment. The idea that random variation is always biased is inconsistent with the definition of random variation. The notion that systematic variation arises from random sampling confuses bias with sampling error. And claiming that all variation is random and uncorrectable ignores the exist­ence of bias that can be identified and corrected.