  We adopt the Pearson cross-correlation measure to analyze the LIGO Hanford
and LIGO Livingston detector data streams around the events GW150914,
GW151012,GW151226 and GW170104. We find that the Pearson cross-correlation
method is sensitive to these signals, with correlations peaking when the black
hole binaries reconstructed by the LIGO Scientific and Virgo Collaborations,
are merging. We compare the obtained cross-correlations with the statistical
correlation fluctuations arising in simulated Gaussian noise data and in LIGO
data at times when no event is claimed. Our results for the significance of the
observed cross-correlations are broadly consistent with those announced by the
LIGO Scientific and Virgo Collaborations based on matched-filter analysis. In
the same data, if we subtract the maximum likelihood waveforms corresponding to
the announced signals, no residual cross-correlations persists at a
statistically significant level.
