What does n denote in a data set?

• A. Mean of a population
• B. Sum of all observations
• C. A single data point
• D. Number of observations in a sample

Answer: (D)

n denotes the number of observations in a data set. It tells you how many data points you have, for example, if you list measurements as x1, x2, ..., xn, there are n values. This count is what you divide by when computing the mean and it influences other calculations like variability and standard error. It’s different from a single data point, which is just one observation, and from the total sum of all observations, which is written with a summation like Σx_i. In practice, lowercase n is used for a sample’s size, while uppercase N is often used for a population size.