The following experiment was performed to create robustness in a process.

$($This is a smaller the better quality characteristic$)$

Which of the $4$ experiments has the least favorable $\frac{S}{N}$ ratio?

$\backslash$table$[[$Experiment$,$N$1,$N$2,$N$3,$N$4,$N$5,$S$/$N $($db$)],[1,1\mathrm{.}3,1\mathrm{.}6,0\mathrm{.}5,1\mathrm{.}2,1\mathrm{.}1,],[2,2\mathrm{.}2,2\mathrm{.}4,0\mathrm{.}4,2,1\mathrm{.}8,],[3,1\mathrm{.}8,1\mathrm{.}7,0\mathrm{.}6,1\mathrm{.}5,1\mathrm{.}3,],[4,3\mathrm{.}9,4\mathrm{.}4,2,4\mathrm{.}1,3\mathrm{.}4,]]$

$1$

$2$

$3$

$4$