Because of the high computational complexity of finding an optimal solution to the -minimum spanning tree, much of the research on the problem has instead concentrated on approximation algorithms for the problem. The goal of such algorithms is to find an approximate solution in polynomial time with a small approximation ratio. The approximation ratio is defined as the ratio of the computed solution length to the optimal length for a worst-case instance, one that maximizes this ratio. Because the NP-hardness reduction for the -minimum spanning tree problem preserves the weight of all solutions, it also preserves the hardness of approximation of the problem. In particular, because the Steiner tree problem is NP-hard to approximate to an approximation ratio better than 96/95, the same is true for the -minimum spanning tree problem.