Test yourself under real exam conditions: 50 timed questions, 60 on the clock, pass mark 70%%. Instant score with a full review of everything you got wrong. Free — no account needed.
Exam details
The mean is the arithmetic average, calculated by summing all values and dividing by the number of values. Formula: x̄ = Σxᵢ / n. It is sensitive to outliers and is the most commonly used measure of central tendency.
The median is the middle value when data is sorted in order. For an even number of observations, it is the average of the two middle values. It is preferred over the mean when data is skewed or contains outliers, as it is more robust.
The mode is the value that appears most frequently in a dataset. A dataset can be unimodal (one mode), bimodal (two modes), or multimodal (more than two modes). If no value repeats, the dataset has no mode.
Standard deviation measures the average amount of dispersion or spread in a dataset relative to the mean. A low standard deviation indicates data points are close to the mean, while a high standard deviation indicates they are spread out. Formula: σ = √(Σ(xᵢ - x̄)² / n) for a population.
Population standard deviation divides by N (total population size), while sample standard deviation divides by n - 1 (degrees of freedom). The sample version uses n - 1 (Bessel's correction) to provide an unbiased estimate of the population variance.