Implications of precision electroweak data

There are two aspects to the 1995 summer update of the combined preliminary electroweak data from LEP and SLC. On the one hand, agreement between experiments and the Standard Model (SM) has improved for the line-shape and the asymmetry data. The \tau widths and asymmetries are now consistent with e--\mu--\tau universality, and all the asymmetry data including the left-right asymmetry from SLC are consistent with the SM (16\%CL). On the other hand, a discrepancy between experiments and SM predictions is sharpened for two observables, R_b and R_c, where R_q is the partial Z boson width ratio \Gamma_q/\Gamma_h. R_b is 3\% larger (3.7\sigma) and R_c is 11\% smaller (2.5\sigma) than the SM predictions. When combined the SM is ruled out at the 99.99\%CL for m_t>170GeV. It is difficult to interpret the 11\pm 4\% deficit of R_c, since if we allow only \Gamma_b and \Gamma_c to deviate from the SM then the precisely measured ratio R_h=\Gamma_h/\Gamma_\ell forces the QCD coupling to be \alpha_s\equiv \alpha_s(m_Z)_{\overline{\rm MS}}=0.185\pm 0.041, which is uncomfortably large. The data can be consistent with the prefered \alpha_s (0.10<\alpha_s