# z test for sum of two percentages as greater than 100

I have a data set in which participants made a choice between two options--option A and option B. Participants were assigned to either choose an option or reject an option (so, there are two conditions--choose vs. reject--in a between subjects design). The prediction is that choose versus reject conditions are not complementary; that is, the rejections will not perfectly mirror the choices, because option B will be chosen and rejected by more than half the people. That is, the percentage of people in the choice condition who choose option B plus the percentage of people in the reject condition who reject option B will be greater than 100. How do I test this? The original article reports a z-statistic, and I have also been told there is a chi-sqaure test for this, but I don't know what the name of the test I want is (nor how to do it in SPSS, but even just some information about what or how to do this would be great, regardless of software). Here is the original text from the article (Shafir, 1993) if helpful, where "Parent B" is option B:

Parent B is the modal choice both for being awarded custody of the child and for being denied it. As predicted, the value of %option B in choice + %option B in reject, for Parent B (64 +55 = 119) is significantly greater than the 100 that we would expect if choosing and rejecting were complementary (z = 2.48, p < .02). Because he/she presents better reasons for both decisions, note that Parent B's likelihood of obtaining custody is significantly greater when subjects decide whom to award than when they ask themselves whom to deny (64% vs. 45%, z = 2.49, p < .02).