For data sets with an odd number of values, this is the "middle" data value if one were to successively cross off pairs from the two ends of the sorted data. For data sets with an even number of values, this is a average of the two data values left after crossing off all other pairs. Using the order statistics, the median equals
\begin{equation*}
y_{\frac{n+1}{2}}
\end{equation*}
if n is odd and
\begin{equation*}
\frac{y_\frac{n}{2} + y_{\frac{n}{2}+1}}{2}
\end{equation*}
if n is even.