Five states were netted by the opposition and the ruling coalition is without its two- thirds majority - which is not just a psychological threshold of its political dominance but also the legislative clout it needs to amend the Constitution.

How did it all go wrong for the ruling Barisan Nasional (BN)? What was labelled a 'wave' of anti-government sentiment is now being called a 'tsunami'.

Mr Ong Kian Ming, a political analyst who does electoral studies, said the tsunami was unleashed by the forces of Chinese and Indian discontent aided by growing Malay disaffection.

To measure the swing's extent, he produced figures using methods created by Harvard political scientist Gary King. The numbers are an average and actual values could be within 5 percentage points higher or lower.

Professor King has a software that conducts statistical analysis on poll results over several years, voter turnout and racial breakdown, to discern trends.

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On the Chinese and Indian fronts, support for BN had traditionally been strong. Even in the 1969 polls - the ruling coalition's previous worst showing - support for non-Malay opposition parties stood at 26 per cent, the same as in 1965.

Mr Ong found that non-Malay support for BN in three elections between 1995 and 2004 barely wavered.

The proportion of pro-BN Chinese voters went up 5 percentage points from 57 per cent between 1995 and 1999, even as the ruling coalition suffered losses due to outrage over then-deputy prime minister Anwar Ibrahim's sacking and imprisonment. The Chinese stayed loyal to the BN, then under Tun Dr Mahathir Mohamad, even as Malays protested.

From 1999 to 2004, support from the Chinese increased by another 3 per cent. Back then, 65 per cent of the community backed BN. Last Saturday, that figure was turned on its head.

Mr Ong estimated that at least 65 per cent of the Chinese this time voted for the opposition. Their anger was fuelled by fears of rising prices, pro-Malay economic policies and Islamisation of the country.

The same story is repeated with the Indians, traditional strong supporters of the government. Through the three elections of 1995, 1999 and 2004, at least eight in 10 Indians supported the government.

Mr Ong estimates that Indian support is now at an all-time low of 47 per cent. The figures bear out in analysis of the latest electoral results.

There are 52 parliamentary constituencies across the country where Chinese and Indian voters form a majority.

Of those, only 13 of them were won by BN. In Penang and Kuala Lumpur, the opposition swept all 16 Malay-minority seats contested.

To some extent, BN had been prepared for an erosion of support among non-Malays. What caught them by surprise was that Malays also deserted them.

Mr Ong's estimates put the swing among Malay votes against the BN at an average of just five percentage points, dropping from 63 per cent to 58 per cent.

But that is enough to turn projected wins into defeat.

Take the Lembah Pantai parliamentary seat for example, where Cabinet minister Shahrizat Abdul Jalil lost to newcomer Nurul Izzah Anwar. Assuming 35 per cent of Chinese, 47 per cent of Indians and 63 per cent of Malays went with BN, Datuk Seri Shahrizat comes out with an edge of 2,000 votes.

Swop the 63 per cent with 58 per cent and all of a sudden, the incumbent is down by 400 votes.

That she ultimately lost by nearly 3,000 votes is an indication that at the extremes, the swing was even larger. Some 41,000 votes were cast in the constituency where 54.5 per cent of the electorate is Malay, meaning Ms Nurul Izzah could have taken up to 47 per cent of the Malay vote.

Nibong Tebal, in Penang, is another example of how a swing by Malay voters could also propel a non-Malay candidate to victory. The constituency is an area where Malays outnumber Chinese but a Chinese candidate beat the Malay incumbent.

If the incumbent, BN's Zainal Abidin Osman, had assumed no swing at all in Malay and Chinese votes from his 2004 victory, he would have calculated a comfortable 8,000 votes ahead.

Include the 30 percentage point swing for the Chinese and he's still only 200 votes behind Parti Keadilan Rakyat's Tan Beng Tee. Add the average 5 percentage point Malay swing and he's down 3,000 votes. And that is exactly how it turned out.

jeremyau@sph.com.sg