Software reliability can be increased by using a diverse pair of programs (1-out-of-2 system), both written to the same specification. The improvement of the reliability of the pair versus the reliability of a single version depends on the degree of diversity of the programs. The choice of programming language has been suggested as an example of a diversity seeking decision. However, little is known about the validity of this recommendation. This paper assesses the effect of language on program diversity. We compare the effects of the choice of programming language as a diversity seeking decision by using programs written to three different specifications in the "UVa Online Judge". Thousands of programs have been written to these specifications; this makes it possible to provide statistical evidence. The experiment shows that when the average probability of failure on demand (pfd) of the programs is high, the programs fail almost independently, and the choice of programming language does not make any difference. When the average pfd of the pools gets lower, the programs start to fail dependently, and the pfd of the pairs deviates more and more from the product of the pfds of the individual programs. Also, we observe that the diverse C/Pascal or C++/Pascal pairs perform as good as or better than the other possible pairs.
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