In country A, the median daily caffeine intake per student who drinks coffee is 120 mg. A university professor who oversees a foreign exchange programme believes that students visiting from country B drink more coffee and therefore have a greater daily caffeine intake from coffee.

On a randomly chosen day, the caffeine intake, in mg, from coffee consumption by each of 15 randomly selected students from country B is given below.

136 \quad 149 \quad 202 \quad 0 \quad 110 \quad 0 \quad 100 \quad 180

0 \quad 187 \quad 0 \quad 0 \quad 138 \quad 197 \quad 115

The professor suspects that the students with zero caffeine intake do not drink coffee, and decides to ignore those students and instead focus on the coffee-drinking students.

\begin{enumerate}[label=(\alph*)]
\item Conduct an appropriate Wilcoxon test at a significance level as close to 5\% as possible. State your conclusion in context. [8]

\item State one limitation of this investigation. [1]
\end{enumerate}

\hfill \mbox{\textit{WJEC Further Unit 5 2024 Q2 [9]}}