In the manufacture of semiconductors, reactive ion etching is a technique whereby the surface of the semiconductor is bombarded with ions to remove unwanted material and to leave the desired structure. In an experiment a set of semiconductors was produced by this technique, and each one was examined to see whether the desired structure was complete or incomplete and also whether the etch depth was satisfactory or unsatisfactory, It was found that in 1078 cases the structure was complete and the etch depth was satisfactory, in 544 cases the structure was complete and the etch depth was unsatisfactory, in 253 cases the structure was incomplete and the etch depth was satisfactory, and in 111 cases the structure was incomplete and the etch depth was unsatisfactory. Use the Pearson chi-square statistic to test whether the completeness of the structure is related to the etch depth, or whether these two factors can be considered to be independent of each other.