The philosophy behind Singapore's approach to crime and punishment has been carefully considered and stated publicly several times before, he said in Parliament.

'Theoretical arguments on our penal policy, bereft of any reference to these key aspects in our system, may make for good sound bites,' said Mr Shanmugam.

'But they do not have any real merit.'

Mr Shanmugam, who is also Second Minister for Home Affairs, was responding to Marine Parade GRC Lim Biow Chuan.

Mr Lim, a lawyer himself, asked if there was a need to review the penal policy after Mr Hwang had critiqued the system in the latest issue of the law society's official magazine.

In his article, Mr Hwang suggested that the Government publish more detailed statistics for social scientists to study the effects of current penal policies.

This will show how effective punishment - such as jail, caning and execution - has been in deterring capital offences, he argued.

He also called for a rethink about policies on crime and punishment at a more fundamental level and wrote that 'Singapore is sadly lacking a principled and transparent penal policy.'

In tackling the criticisms, Mr Shanmugam rebutted each of Mr Hwang's arguments point by point.

First, he said that Mr Hwang did not state exactly what data had not been published.

Mr Shanmugam pointed out that the Government regularly releases statistics on crime and drug offences on an aggregated basis.

He noted that the authorities have often worked with independent researchers, including students, and given assistance to serious researchers who want to do research on the penal system.

For example, the Prisons Department collaborated with National University of Singapore on a research study of the needs assessment of aftercare services for ex-offenders and their families in 2007.

'To suggest that there are inadequate published statistics and that that has prevented proper research is untenable,' said Mr Shanmugam

He also responded to Non-constituency MP Sylvia Lim who said the Government has been reluctant to publish figures on ethnicity and crimes.

Mr Shanmugam said there was no reason to publish such figures on an aggregated basis and questioned the need to release such information publicly.

'How in the world would publishing details on ethnic composition on aggregated basis help in such penological research?' he said.

'As a matter of common sense if you want to do any research, you need to go down to the ground and get access to the specific prisoners which, obviously as a matter of confidentiality, prisons cannot publish and make available to the whole world at large.'

Mr Shanmugam also rejected Mr Hwang's second claim that the lack of statistics has led to the penal system being unprincipled.

He said the system is based on sound principles that have been articulated in public several times before.