The tyranny of averages is a phrase used in applied statistics to describe the often overlooked fact that the mean

Mean

In statistics, mean has two related meanings:* the arithmetic mean .* the expected value of a random variable, which is also called the population mean....

 does not provide any information about the distribution of a data set or skewness

Skewness

In probability theory and statistics, skewness is a measure of the asymmetry of the probability distribution of a real-valued random variable. The skewness value can be positive or negative, or even undefined...

, and that decisions or analysis based on this value—as opposed to median

Median

In probability theory and statistics, a median is described as the numerical value separating the higher half of a sample, a population, or a probability distribution, from the lower half. The median of a finite list of numbers can be found by arranging all the observations from lowest value to...

 and standard deviation

Standard deviation

Standard deviation is a widely used measure of variability or diversity used in statistics and probability theory. It shows how much variation or "dispersion" there is from the average...

—may be faulty.

A UN

United Nations

The United Nations is an international organization whose stated aims are facilitating cooperation in international law, international security, economic development, social progress, human rights, and achievement of world peace...

 Development Program

United Nations Development Programme

The United Nations Development Programme is the United Nations' global development network. It advocates for change and connects countries to knowledge, experience and resources to help people build a better life. UNDP operates in 177 countries, working with nations on their own solutions to...

press release discusses a real world example:

A new report launched 1 July [2005] warns that in Asia and the Pacific, the rising prosperity and fast growth in populous countries like China and India is hiding widespread extreme poverty in the Least Developed Countries (LDCs). The result is potentially very debilitating to development efforts in the 14 Asia-Pacific LDCs.

This “tyranny of averages” to which the report refers tends to mask the stark contrast between the Asia-Pacific LDCs’ sluggish economies and the success of their far more populous neighbours.