  We present a meta-analysis of recent muon density measurements made by eight
air shower experiments which cover shower energies ranging from PeV to tens of
EeV regarding the muon puzzle in extensive air showers. Some experimental
analyses reported deviations between recorded and simulated muon densities in
extensive air showers, and others reported no discrepancies. Comparisons
between experiments were made using a universal reference scale based on the
relative difference to simulated proton and iron initiated air showers. We have
applied a cross-calibration of energy scales between experiments based on the
isotropic flux of cosmic rays as a reference. Above 10 PeV, most experimental
data show a muon excess with respect to simulated air showers, including those
performed with the recent post-LHC high-energy interaction models. The
discrepancy increases with the shower energy with a slope 8 sigma away from the
predictions by EPOS-LHC and QGSJet-II.04. The effect of measurements being made
at different zenith angles and energy threshold of muons across different
experiments will be addressed.
