MUMBAI: Tata Group invested USD 9 billion in its businesses globally in 2015-16, even as its worldwide revenue fell marginally to USD 103 billion due to commodity market slowdown and volatile currencies among other reasons, the diversified conglomerate's chief Cyrus Mistry said today.Addressing the Annual Group Leadership Conference ( AGLC ) of the steel-to-software conglomerate, Mystry also announced a new leadership competency model based on key competencies to develop and identify leaders within the group firms and outlined a new framework focussed on 'happiness at work'.The total investments by the over 100 group companies in the last three years totalled to over USD 28 billion, said Mistry, Chairman of the main holding company Tata Sons Ltd Addressing the top leadership and senior management personnel from various Tata group companies, Mistry said the conglomerate's total revenues dropped 4.62 per cent to USD 103 billion in fiscal year 2015-16, from USD 108 billion in the previous financial year.He attributed the marginal fall in revenue to global political uncertainties, a steep reduction in commodity prices, and volatility in currencies.International revenues at around USD 70 billion constituted 69 per cent of the group's revenues.Sixteen companies in the group registered a turnover of over USD 500 million each, with ten of these registering a turnover of over USD 1 billion.The market cap of Tata group's 29 listed companies was down by 7.4 per cent to USD 116 billion as against 9.4 per cent correction in the stock market benchmark BSE Sensex In furtherance to a vision for 2025 announced at the AGLC, held every year on founder JRD Tata's birth anniversary, Mistry also outlined a 'Tata Quality of Life' framework that will focus on 'happiness at work'.Speaking at the NCPA auditorium near its global headquarters 'Bombay House ' here, Mistry further said the set of values that define the Tata Group have also been refreshed with the changing times to include the virtue of "pioneering"."This value has always been core to the Tata group's approach to business and is reflected in many inspiring endeavours," Mistry said.