This page enables you to calculate Shapley-Shubik indices exactly using the program ssdirect which employs the fundamental definition directly. The direct enumeration algorithm performs a search over all the possible voting outcomes and finds all swings for each one.
Reference: Shapley and Shubik (1954).
This algorithm has the advantages of simplicity and of giving exact values for the power indices. Its major disadvantage is that it has exponential time complexity because the computing time required doubles each time an extra member is added. In practice this means that it is suitable for small weighted voting bodies but is practically infeasible for medium sized or larger ones. In practice the web implementation here is not feasible if the number of voters exceeds about 25.
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