Spot the flaw. Since 1953, when Tenzing Norgay and Edmund Hillary reached the summit of Mount Everest, many climbers have attempted to scale the world’s two highest mountains, Everest and K2. Norgay and Hillary aided their climb by bringing supplemental oxygen in tanks, and some later groups have attempted to outdo the originals by trying the ascent without supplemental oxygen. From 1978 to 1999, in fact, 159 teams comprising 1173 team members attempted to climb either Everest or K2. The numbers of individuals who either survived or died during those attempts is given in the following table (data from Huey and Eguskitza 2000):

A x² contingency test on these data calculated x² = 7.694x² = 7.694 with one degree of freedom, which corresponds to P=0.0055  The null hypothesis is that oxygen use has no effect on survivorship during these expeditions. What’s wrong with this analysis?

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Survived Survived Did not survive Did not survive Column totals Column totals Supplemental 020₂ 10451045 3232 10771077 No supplemental 0202 8888 88 9696 Row totals 11331133 4040 11731173