  The weak decay parameter $\alpha_-$ of the $\Lambda$ is an important quantity
for the extraction of polarization observables in various experiments.
Moreover, in combination with $\alpha_+$ from $\bar\Lambda$ decay it provides a
measure for matter-antimatter asymmetry. The weak decay parameter also affects
the decay parameters of the $\Xi$ and $\Omega$ baryons and, in general, any
quantity in which the polarization of the $\Lambda$ is relevant. The recently
reported value by the BESIII collaboration of $0.750(9)(4)$ is significantly
larger than the previous PDG value of $0.642(13)$ that had been accepted and
used for over 40 years. In this work we make an independent estimate of
$\alpha_-$, using an extensive set of polarization data measured in kaon
photoproduction in the baryon resonance region and constraints set by spin
algebra. The obtained value is 0.721(6)(5). The result is corroborated by
multiple statistical tests as well as a modern phenomenological model, showing
that our new value yields the best description of the data in question. Our
analysis supports the new BESIII finding that $\alpha_-$ is significantly
larger than the previous PDG value. Any experimental quantity relying on the
value of $\alpha_-$ should therefore be re-considered.
