Western Region Climate Center at http://www.wrcc.dri.edu/enso/ensodef.html
Climate Diagnostics Center at http://www.cdc.noaa.gov/people/cathy.smith/best/
Climate Prediction Center at http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ensoyears.html
Multivariate ENSO Index from Climate Diagnostics Center at: http://www.cdc.noaa.gov/ENSO/enso.mei_index.html

An event consensus was arrived at by choosing years which appeared on three of the four above lists.  It should be noted that there is obviously some crossover of the variables used in the various methodologies and no attempt has been made to give a weight of one list over another.   When WRCC, CPC and MEI all indicated W+ and CDC gave a W (their strongest category) then that season was considered a strong event.  Otherwise the strength was determined from the "average" of the strength of chosen events.  The resultant data is expressed in Table 1 (below).

Table 1.  Consensus List of El Niño and La Niña Years