The United States Chief Justice, John Roberts, does not think that New Zealand having a written constitution would lead to judges making decisions based on political preferences.
Mr Roberts has been visiting New Zealand this week and teaching a programme at Wellington's Victoria University.
During a public discussion at the university, John Roberts was asked about proposals in New Zealand for a constitution and whether that could lead to judges having political bias in their decision making.
He told the crowd that in the US the constitution tended to limit the ability of judges to introduce their own personal predilections.
"I wouldn't think having a written document would give the judges broader scope and present a more significant problem in terms of introducing any personal preferences.
"In our system it's been, at least in many instances - many but certainly not all - having more of a constrainting purpose and effect."
In the US, Supreme Court justices, court of appeals judges, and district court judges are nominated by the President and then confirmed by the Senate.
John Roberts was asked how he would design a system to appoint judges.
He replied that most judges would say they liked the current system because they had come through it.
"I think the system that the founding fathers of my country established is a good one, that the President, the chief executive officer of government, answerable to all the people, is the one that makes the nomination, but that a separate body...has to give its assent.
"I think that's a wonderful, an important check, a balanced approach - each of the two political branches coming together and selecting the membership of the third branch, that's the theory.
"In practice I think we are experiencing a bit of a rocky road because the judicial process has become overly politicised, it didn't used to be that way as a general rule.
"I think there is a lack of understanding about what sort of things people should be looking at when they're deciding who should be a judge.
"Judges are not politicians and they should not be scrutinised as if they were, you are not electing a representative so you are not entitled to know what their views on political issues are."