Which parameter represents proportional systematic error?

• A. Slope
• B. Intercept
• C. R
• D. P-value

Answer: (A)

Proportional systematic error is bias that grows with the size of the true value, so it shows up as a change in how the measured value scales with the actual value. In a linear relationship model, measurements are written as measured = intercept + slope × true value. The intercept captures a constant, fixed offset, while the slope captures proportional changes—how much the measurement changes in proportion to the true value. Therefore, the slope is the parameter that represents proportional systematic error. The intercept would reflect a constant bias, the correlation coefficient R assesses how well the data fit a line rather than bias, and the P-value indicates statistical significance rather than a bias type.