= Solution
For a measurement of the cross-section ratio with <standard deviation> $0.019R$, the separation of the fourth-lepton prediction from the ordinary prediction is
$$
\boxed{n_{\rm ratio}=\frac{|R'-R|}{0.019R}
=\frac{0.0191107}{0.019}=1.006\simeq1.0.}
$$
Thus the peak-ratio model predicts only about a one-standard-deviation shift in this observable. In contrast, the direct <Z boson> width changes by $167+84=251$ MeV, giving
$$
\boxed{n_{\Gamma_Z}=\frac{251}{2.3}=109.1.}
$$
Under these assumptions the direct width measurement is overwhelmingly more sensitive. These are separate expected displacements, using the supplied experimental uncertainties and fixed theoretical inputs; they are not a combined statistical significance. The $501/3$ single-neutrino normalization and the peak-energy assumption are the same as in <4/e>. If the alternative literal $501$ MeV per <neutrino> premise were used, the corresponding displacements would instead be $12.3$ and $254$ standard deviations, illustrating why that normalization must be stated.
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