Most of us are aware, if only vaguely, of public opinion polls. They pop up on the television news and tell us which political parties, and leaders, are up and which are down.
We are possibly less aware, however, of another role that polling plays in our politics.
Professional pollsters, and their clients in the political parties, employ what they call qualitative polling to measure trends in the way the public looks at particular issues.
What are called "focus groups", volunteers chosen to be as representative as possible of the wider electorate or of particular parts of it, are assembled to discuss issues of the day in the presence of an expert observer who then reports back on what was said about, say, the government's latest policy initiative.
John Key's Government made an art form of this, but it was not unique in that. A new policy was often be floated, to test the waters, usually by Key himself or, in past times, Helen Clark. What then happens is that the focus groups are consulted and, depending on what they say, the policy is implemented or changed or simply abandoned.
But it is not just policy options that are tested in this way.
The major political parties need to know how acceptable to the public are their major representatives. They will constantly test the public reaction to, say, a Judith Collins or a Paula Bennett. The politicians themselves are often unaware that these tests take place and even less of how they are rated.
I recall that, when I was active in British politics and running general election campaigns, polling of this kind revealed that one of our most senior figures was a complete turn-off. We kept it from him, but he no doubt wondered why he was rarely called upon to appear on our screens.