AP Psychology Practice Test 2025 - Free AP Psychology Practice Questions and Study Guide

The measurement of standard deviation is fundamentally about how much individual scores in a data set vary or deviate from the mean score. It provides a quantitative measure of the spread or dispersion of scores, indicating the extent to which each score differs from the average. A smaller standard deviation indicates that the scores are close to the mean, while a larger standard deviation signifies that the scores are more spread out.

Understanding standard deviation is crucial in statistics because it helps to assess data variability and can inform decision-making processes in various fields, including psychology. Knowing how far scores are from the mean allows researchers to better interpret the reliability and significance of their findings.

The other options address different statistical concepts. The difference between the highest and lowest scores refers to the range, not standard deviation. The total sum of all scores does not provide insight into variability, and variance is itself a related but distinct measure that is calculated as the average of squared deviations from the mean, while standard deviation is the square root of that variance and provides a more interpretable measure of spread.