Which statement correctly describes random variation versus systematic variation (bias)?

• A. Random variation arises from chance; systematic variation is biased and requires correction.
• B. Random variation is always larger than systematic variation.
• C. Systematic variation occurs by chance; random variation is biased.
• D. Random variation can be ignored; systematic variation is due to measurement error.

Answer: (A)

Random variation reflects fluctuations that come from chance in sampling and measuring. It makes data spread around the true value, and this spread becomes easier to manage as you gather more data or take repeated measurements, improving precision. Systematic variation, or bias, is a consistent directional error that pushes results away from the truth. Because it isn’t due to random chance, it doesn’t vanish with larger samples; it needs to be addressed through better study design, calibration, standardized procedures, blinding, or statistical adjustment.

That’s why the statement that random variation arises from chance and systematic variation is biased and requires correction best captures the distinction. The other options mischaracterize the relationship in important ways: random variation isn’t always larger than bias; systematic variation isn’t due to chance; and random variation shouldn’t be ignored—its presence affects precision and confidence in the estimate.