That comparison was of IBM relative to named companies covered by annual
surveys in the publication "Occupational Pensions". It showed that the
general practice was for pensions to retain their value, but with IBM
noticeably worse than that.
There is another respected source of information on UK pension erosion,
the Watson Wyatt Index of Pension Increases. This covers nearly 60 big
companies, although it does not name them. They are probably almost the
same set of companies as those that the IBM Trust compares itself against
when assessing its investment performance.
The Watson Wyatt message is essentially that companies have not eroded
pensions - their value has been maintained over the period since 1984.
A couple of minor points are worth noting. We do not know if IBM is in
the Watson Wyatt Index, but if it is then the Index will slightly underestimate