The Annual Survey of Hours and Earnings (ASHE) replaced the New Earnings Survey (NES) in 2004 and collects information supplementary to that in NES, therefore ASHE results from 2004 onwards cannot be compared directly to data from previous years.
ASHE results from 2006 onwards are also discontinuous with earlier results, due to a small number of methodological changes having been introduced into the sample design, to improve the quality of the results.
From 2012, the Standard Occupational Classification 2000 (SOC2000) used for ASHE has been replaced by the Standard Occupational Classification 2010 (SOC2010).
Since the SOC forms part of the methodology by which ASHE data are weighted to produce estimates for Northern Ireland, this has caused a further discontinuity in the ASHE time series.
Therefore, the revised estimates for 2011, and all subsequent provisional and revised estimates, are not directly comparable to earlier results.