Is thirty per cent the tipping point?

I recently took part in a live chat at FT.com asking why there aren't more women in the boardroom. The chat stemmed from a comment piece by London Business School's Lynda Gratton, who argues that 30 per cent of senior positions need to be held by women before an organisation can fully realise its potential female talent. Although Professor Gratton's background is financial, her argument would seem to make sense for all sectors, including media.