The median life expectancy value listed in the ASHRAE chart is the middle value in a dataset when it is arranged in order. In contrast, the average life expectancy would be the sum of all values divided by the number of data points. Median values are often used in cases where the data is not normally distributed, as they are more representative of the typical value. In the context of HVACR equipment life expectancy, the median value provides a more realistic expectation of equipment lifespan.