The study found that the prevalence of professional non-executive directors (NED)--defined as someone who holds two or more non-executive positions on S&P/ASX 100 boards--has increased over the previous period.

In 2005, for example, 173 individuals were appointed non-executive directors of an S&P/ASX 100 company, of whom 105 already held or had previously held a S&P/ASX 100 company directorship. Well over one-half of new non-executive director appointees in 2005 were therefore experienced large-company directors, the study found.

By comparison, in 2004, 25 of 93, or 27 percent, of new non-executive appointees were past or present S&P/ASX 100 company directors. Consequently, the study concludes that a key qualification for gaining entry to an S&P/ASX 100 company board in 2005 was to hold or have held a director position.

This trend also was reflected in the growing number of S&P/ASX 100 company directors holding multiple board seats within the top 100 firms. Their numbers have been growing steadily since 2001, when 72 professional NEDs held 164 board seats, or roughly 31 percent of all S&P/ASX 100 company board seats.

In 2005, 117 professional NEDs held 269 board seats, accounting for 42.8 percent of all board seats at the country’s top 100 companies. This was a modest though notable increase over 2004, when 99 professional NEDs accounted for 39.4 percent of all top 100 board seats.

Professional NEDs are well represented among the ranks of female non-executive directors, the study found. Of the 57 women on S&P/ASX 100 company boards, 35, or 61.7 percent, held more than one board seat at an ASX-listed company, compared with 40.9 percent of male S&P/ASX 100 directors.

The survey also charted a small drop in the proportion of seats held by independent directors. In 2004, independent directors accounted for 50.4 percent of all top 100 directorships, compared with 47.4 percent in 2005. The proportion of non-executive directorships, meanwhile, rose marginally from 79.6 percent in 2004 to 81.2 percent in 2005.

In 2004, ACSI considered all directors with more than nine years' service to be affiliated, whereas only those directors who had spent more than 20 years on a board were considered to be affiliated for reasons of tenure in 2005. If the new classification is used, the proportion of board seats held by independent non-executive directors in 2005 rose to 64.9 percent, however.