An annual study by the Australian Council of Super Investors (ACSI) has raised investors' concerns over the make up of Australian boards. 

The study reviewed the board composition and non-executive director remuneration of S&P/ASX 100 companies, and found there is an ongoing tendency for boards to appoint from within.

During the 2007 financial year, 55 percent of non-executive directors appointed to a Top 100 company board were already directors of a Top 100 company, or had been in the past.

The average length of tenure for a non-executive director was 5.1 years, substantially lower than the average 6.9 year tenure of an executive director.

"It is likely that a non-executive director, who has been at a company for a relatively short period, is going to be less willing to question an experienced chief executive or executive director than a director who was involved with appointing that chief executive," ACSI chief executive Ann Byrne said.

Another concern was the lack of representation of women on Australian boards.

Showing a slight fall from 2006, women held 12.4 percent of all Top 100 company board seats, and accounted for 10.4 percent of all Top 100 company directors.

Despite these concerns, Byrne said Australian boards had succeeded in making sure they were majority independent.

"The fact that the average S&P ASX 100 board is clearly majority independent... indicates that boards are aware of the need for independent oversight and review of management," she said.

The annual research has tracked board composition since 2002.