JAMB Economics 2017 Paper

Concept:The formula calculates the average absolute deviation of data values from the arithmetic mean in a grouped frequency distribution.Explanation:In the formula, $x$ is each observed value, $f$ is its frequency, $\bar{x}$ is the arithmetic mean, and $N$ is the total number of items, where $N = \sum f$.The expression $\frac{\sum f(x-\bar{x})}{N}$ measures the average distance between the data values and the mean.For grouped data, mean deviation is written as $\frac{\sum f|x-\bar{x}|}{N}$, where the vertical bars show that only the absolute values of the deviations are summed.It is not variance or standard deviation, because those formulas square the deviations as $(x-\bar{x})^2$.It is not a quartile, since a quartile is a positional value and is not obtained from deviations about the mean.Hence, the formula is used for mean deviation.Answer:D. mean deviation