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:

$\begin{array}{l}
\text { Kruskal-Wallis Test on viral load }\
\begin{array}{lrrrr}
\text { vaccine } & \mathrm{N} & \text { Median } & \text { Ave Rank } & \mathrm{Z} \
1 & 16 & 5.530 & 18.6 & -0.18 \
2 & 13 & 5.030 & 11.2 & -3.25 \
\text { sham } & 8 & 6.860 & 32.5 & 3.98 \
\text { Overall } & 37 & & 19.0 &
\end{array}
\end{array}$

$\begin{array}{llll}
\mathrm{H}=19.29 & \mathrm{DF}= & \mathrm{P}= & \
\mathrm{H}=19.30 & \mathrm{DF}= & \mathrm{P}= & \text { (adjusted for ties) }
\end{array}$ What is the P-value of the Kruskal-Wallis test for these data?

Question

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:
​
$\begin{array}{l}
\text { Kruskal-Wallis Test on viral load }\
\begin{array}{lrrrr}
\text { vaccine } & \mathrm{N} & \text { Median } & \text { Ave Rank } & \mathrm{Z} \
1 & 16 & 5.530 & 18.6 & -0.18 \
2 & 13 & 5.030 & 11.2 & -3.25 \
\text { sham } & 8 & 6.860 & 32.5 & 3.98 \
\text { Overall } & 37 & & 19.0 &
\end{array}
\end{array}$

$\begin{array}{llll}
\mathrm{H}=19.29 & \mathrm{DF}= & \mathrm{P}= & \
\mathrm{H}=19.30 & \mathrm{DF}= & \mathrm{P}= & \text { (adjusted for ties) }
\end{array}$ What is the P-value of the Kruskal-Wallis test for these data?

Quizplus · Accepted Answer

The P-value is not explicitly given, but the fact that the Kruskal-Wallis test statistic $H$ is provided as 19.29 or 19.30 (adjusted for ties) without the corresponding P-value suggests that the P-value is very low. Typically, an $H$ value this high would correspond to a P-value less than 0.01, indicating a statistically significant difference between the groups.

A Research Team Investigated the Protective Effect of Two Variants