Prosenttiilien

Prosenttiilien, also known as percentiles, are statistical measures that divide a data set into one hundred equal parts. Each percentile indicates the value below which a given percentage of observations fall. For example, the 50th percentile, or median, is the value below which 50 % of the data lie. Percentile ranks are commonly used in educational testing, health assessments, and market research to compare individual scores or measurements relative to a reference population.

The calculation of a percentile involves sorting the data and determining the position of the desired percentile using the formula (P/100) × (N + 1), where P is the percentile and N is the number of observations. When the calculation yields a fractional index, interpolation between adjacent data points is used to estimate the percentile value. Different organizations adopt slightly varying conventions, particularly for small data sets, but the general principle remains consistent.

In educational contexts, percentile scores help educators identify students who perform above or below national norms. In health, percentiles of growth charts indicate how a child's height or weight compares with peers of the same age and sex. In market research, consumer surveys often report percentile rankings to gauge satisfaction or popularity.

Understanding prosenttiilit allows researchers and practitioners to interpret responses and measurements in a relative framework, enabling comparisons across diverse populations and over time.