The most common lower bound to the reliability of a test is Cronbach’s alpha. However, several lower bounds exist that are definitely better, that is, higher than alpha. An overview is given as well as an algorithm to find the best: the greatest lower bound.
"Beyond Alpha: Lower Bounds for the Reliability of Tests,"
Journal of Modern Applied Statistical Methods: Vol. 9
, Article 11.
Available at: http://digitalcommons.wayne.edu/jmasm/vol9/iss1/11