When Data Are Summarized in a Frequency Distribution, the Median

Short Answer

When data are summarized in a frequency distribution, the median can be found by first identifying the median class (the class that contains the median). We then assume that the values in that class are evenly distributed and we can interpolate. This process can be described by $$\text { median } = ( \text { lower limit of median class } ) + ( \text { class width } ) \left( \frac { \frac { \mathrm { n } + 1 } { 2 } - ( \mathrm { m } + 1 ) } { \text { frequency of median class } } \right)$$ where n is the sum of all class frequencies and m is the sum of the class frequencies that precede the median class. Use this procedure to find the median of the frequency distribution below:

$$\begin{array} { c | c } \text { Score } & \text { Frequency } \\\hline 50 - 59 & 21 \\60 - 69 & 24 \\70 - 79 & 25 \\80 - 89 & 17 \\90 - 99 & 13\end{array}$$

A) 71.6
B) 74.5
C) 71.8
D) 72.2