What does standard deviation measure in a set of data?

Standard deviation is a statistical measurement that quantifies the amount of variation or dispersion in a set of numerical data. It indicates how much individual scores in a data set deviate from the mean (average) score. A low standard deviation means that the data points tend to be close to the mean, whereas a high standard deviation indicates that the data points are spread out over a wider range of values. This measurement is particularly useful in educational psychology as it helps researchers and educators understand the degree of variability in test scores or other assessments, thereby providing insight into student performance and learning outcomes. This focus on the spread of scores is essential for interpreting the reliability and consistency of data.