The regression - to - the - mean concept describes which phenomenon?

• A. The tendency for the occurrence of crashes to fluctuate up and down in specific years, but converge to a long-term mean
• B. Seasonal pattern
• C. Random yearly variation with no trend
• D. Exponential growth in crashes

Answer: (A)

Regression to the mean is the tendency for extreme outcomes to move closer to the long-term average in subsequent observations. In road crash data, a year with unusually high crashes is likely to be followed by years with counts that are nearer to the historical average, because the extra spike was partly due to random factors that aren’t consistently present. Once those random influences subside, the numbers drift back toward the average. This differs from a seasonal pattern, which would show regular within-year fluctuations, and from pure random variation with no trend, which wouldn’t systematically pull extreme years back toward the mean. It also isn’t exponential growth, which would show accelerating increases rather than a pull toward a stable average.