A Research Team Investigated the Protective Effect of Two Variants

Multiple Choice

A research team investigated the protective effect of two variants of a vaccine against the simian immunodeficiency virus (SIV) in rhesus monkeys. They measured the viral load (in log scale) of monkeys randomly assigned to either a vaccine variant or a sham (fake) vaccine. Here is a partial software output for a Kruskal-Wallis test on the data:
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Kruskal-Wallis Test on viral load
$\begin{array} { l r r r r } \text { vaccine } & \mathrm { N } & \text { Median } & \text { Ave Rank } & \mathrm { Z } \\ 1 & 16 & 5.530 & 18.6 & - 0.18 \\ 2 & 13 & 5.030 & 11.2 & - 3.25 \\ \text { sham } & 8 & 6.860 & 32.5 & 3.98 \\ \text { Overall } & 37 & & 19.0 & \end{array}$
$$\begin{array} { l } \mathrm { H } = 19.29 \quad \mathrm { DF } = \quad \mathrm { P } = \\\mathrm { H } = 19.30 \quad \mathrm { DF } = \quad \mathrm { P } = \quad \text { (adjusted for ties) } \\\end{array}$$ The null hypothesis of the Kruskal-Wallis test is that viral load has the same distribution in all groups. What is the alternative hypothesis?

A) Not all three mean viral loads are equal.
B) The mean viral load is larger for the sham treatment than for the two vaccines.
C) The median viral load is larger for the sham treatment than for the two vaccines.
D) The viral loads are systematically larger in some treatments than in others.