Gordon Brown’s Pre-Budget Report is due in a few days and look at you, you’re not even half ready. I am going to help you prepare by asking you to do a little mental maths. It will be worth the investment of time, I promise. It will only take a few moments and will assist you in understanding not only the Pre-Budget Report but also the next election campaign. What an offer.

So, you have five seconds for this one and not a second more. Multiply:

2 x 3 x 4 x 5 x 6 x 7 x 8

Good. Write down the answer and ask a friend to calculate, again in no more than five seconds, the answer to the following:

8 x 7 x 6 x 5 x 4 x 3 x 2

Now, compare your answers. You will immediately notice two things. First, you both got it wildly wrong. The correct answer is 40,320 and neither of you was close, since you both underestimated it. The second characteristic of the two answers is that you produced a smaller number than your friend. (If this didn’t work, by the way, don’t write to me. Two economists won a Nobel prize for work based on this observation. Write to them and ask them to send the prize back.)

Let me tell you what’s going on. You were anchoring. You began the calculation and had managed to multiply, say, 2 by 3 by 4. This anchored you at 24. Although you realised that the numbers continued to ascend and tried to take account of that, you didn’t remotely multiply by enough. And your friend? They were anchored at about 400 as the numbers descended and still didn’t multiply by enough.

One of those Nobel laureates I talked about, Daniel Kahneman (the other was Amos Tversky), has given an even more striking example of anchoring. He asks groups to give the last four digits of their social security number and then estimate the number of doctors in New York. A strong correlation is observed between the two (logically unrelated) numbers that are provided. The bigger their social security number the more doctors they thought there were.

In his book Inevitable Illusions, Massimo Piattelli-Palmarini explains the role that anchoring plays in decision-making. Instead of thinking through our view of an issue from the beginning, we think of it in terms of departures from a baseline and we are remarkably suggestible about what that baseline is.

The way a question is put to us, the way it is framed, is everything. Clinical data suggest that when doctors were told that there was a mortality rate of 7 per cent within five years for a certain operation they hesitated to recommend it. But if they were informed that 93 per cent would survive after five years, they were much more inclined to go ahead.

I have explained this in some detail because of its powerful impact on politics. In the run-up to the 1997 general election the Labour Party was incredibly careful not to depart too far from Tory orthodoxy. Its two central pledges were to retain income tax rates at their existing level and to match Conservative spending plans. This was regarded as essential to securing its election.

In the years after Labour’s election the Government raised taxes and spending. The Tories proposed a return to a more frugal approach — lowering taxes so that they more nearly approximated to the 1997 rates and curbing the growth of public spending. But it didn’t work. It was seen as faintly dangerous.

So why was a tax and spending settlement, which was seen as an election winner in 1997, seen as an election loser by 2001? Had public opinion changed so much? No, what had changed was the baseline. When Labour won office, it also won the right to frame the political question. And this changes the political game fundamentally.

In a pamphlet published last week, the former Conservative ad man Lord Saatchi lamented the decline of ideology. He questioned the Tory party’s move to the centre and urged a more robust approach. He lampoons today’s arid political debate rather effectively. But he takes no account whatever of the ability of governments to frame the choices that voters make and the way that this limits the opposition’s room for manoeuvre.

In anything other than a meltdown (of the sort seen in 1979), politicians who offer sharp departures from current practice are often seen by voters as threatening, even if the very same voters could later be persuaded by a governing party that the very same policies were a good idea.

There is one politician who understands about anchoring very well. It is his quiet political strength. Meet the Right Honourable Gordon Brown, MP. You can expect him to make full use of it in his Pre-Budget Report next week and to base his election campaign on it, too.

Both the Chancellor and his sidekick, the Financial Secretary, Ed Balls, frequently refer to “dividing lines” with the Conservative Party. Their aim is to establish a baseline policy from which Mr Cameron will depart. Whether this baseline is, objectively, popular matters less than whether the Tories can be tempted into rejecting it.

So, for example, before the election Mr Brown will provide his plans for growth in public spending. Whatever they are, whether or not they are sensible in their own right, the Conservative Party’s policy will be judged against them. Undershoot Brown’s plans and the Tories will be accused of cuts, overshoot and there will be talk of tax rises. Mr Brown will have set the baseline.

I am not saying this because I like it. I am saying this because that is how we think, how voters think.

Next week, when Mr Brown gets to his feet, we will be looking to him to provide some answers on the economy. He will be seeing his task rather differently. He will be looking to set some questions.

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