  A model independent analysis is made using the LEP and SLD data on Z decays
available at the end of 1996. The effective weak coupling constants of leptons,
c quarks and b quarks are extracted. Except for the right-handed b quark
coupling, they all agree well with the predictions of the Standard Electroweak
Model for $m_t = 172$ GeV and $m_H = 263$ GeV. The right-handed b quark
coupling is found to be 42% and 3.2 standard deviations above the Standard
Model prediction.
