  We prove a general lower bound on the average-case complexity of Shellsort:
the average number of data-movements (and comparisons) made by a $p$-pass
Shellsort for any incremental sequence is $\Omega (pn^{1 + 1/p)$ for all $p
\leq \log n$. Using similar arguments, we analyze the average-case complexity
of several other sorting algorithms.

Data Structures and Algorithms;Computational Complexity