The NISA Pension Surplus Risk index fell 0.3 percentage points to 6.6% in August, the second consecutive monthly decline.
During August, the volatility of the index's asset component fell to 7.6% from 7.8%, while the liability component's volatility fell 0.4 percentage points to 6.9%.
The index fell to its historic low 11 months ago when the September 2017 volatility was 6.5%.
The average plan funded status rose to 92.6%, its highest mark since September 2008, from 92.4% in July. However, at that point in 2008, the average funded status of the observed plans had fallen 2.4 percentage points from the month before and as much as 12.4 percentage points over the previous 12 months.
August data show that among the observed corporate pension plans, the 11 in the health-care sector were the most volatile at 8.3%, while consumer discretionary companies (8) were the least volatile at 3.4%. The financial sector plans (16) were the best funded at 105%. The materials (3) and telecommunications (7) sectors, were relatively worse off at 85% funded and 87% funded, respectively. Historical sector data were not available to give further context.