Simon gets schooled

Poor old Simon Bridges, he really cannot get a break. He tried to to look cool and intelligent in Question Time and failed.

It all started on Monday with Question 1 when Bridges challenged Ardern on rental growth under her government:  Quote.

Hon Simon Bridges: How many dollars a week has the median rent increased under her Government?

Rt Hon JACINDA ARDERN: I’ve actually seen some of the statements from the member on rental increases, and what I wanted to point out was that the numbers that he’s used have been quite selectively chosen. When you look across the country at the—and I can give a percentage rather than a numerical figure to the member; but, if he puts it on notice, I’ll bring a dollar figure for him—geometric mean growth, that’s remained relatively steady. So in September 2018, that was 4.8 percent; September 2017, it was also 4.8 percent; September 2016, it was 4.5 percent; September 2015, 5 percent—you get the picture. So it is fair to say rents have consistently increased over the years. Obviously, the member will know the most significant driver of that is supply, and this Government is focused on fixing that issue. End quote.

Ardern lists the rental growth rates for the previous 3 years: 5%, 4,5%, 4,8% and 4.8% under her government which seems pretty normal.  Quote.

Hon Simon Bridges: Well, is she aware that the median figure is some $30—2½ times higher than the year prior, and that, even using the mean, rents have gone up $26 a week under this Government compared to just $13 under the previous?

Rt Hon JACINDA ARDERN: I know that that member chose one month and used figures which aren’t an accurate way of capturing what’s happening in our rental market. I absolutely accept that rents have increased—I accept that. What I do not accept is that somehow the last Government had nothing to do with the issue that we are now facing. There is a supply issue. That was a Government who got rid of State houses and that did not address the lack of supply. Unlike that Government, we are turning the ship around; it just takes a bit of time to build houses.

Hon Simon Bridges: Is she seriously disputing the Ministry of Business, Innovation and Employment figures that show, on a median basis, rent has gone up 2½ times, and on a mean basis it’s doubled?

Rt Hon JACINDA ARDERN: No. What I am referring to, though, is the geometric mean growth, which is the most accurate average, because the arithmetic means are too sensitive to changes in the higher value. Again, I’m not arguing with the member over whether rents have gone up; what I am arguing over is whether or not we’ve got a solution that the last Government didn’t even try? End quote.

So Ardern has been properly briefed and threw in some words that she has probably never used before – after all, she did not know what GDP was – and it appears to have taken the wind out of Bridges’ sails.  Quote.

Hon Simon Bridges: How do we calculate geometric mean growth? End quote.

This is interesting. Does he know the answer and is trying to trip Ardern, or is this actually a genuine question?

Ardern is not going to rise to the bait and brushes him off without revealing whether she really understands the concept of a geometric mean or not.  Quote.

Rt Hon JACINDA ARDERN: What I’ve argued here is that when taking into account spreading over that period of time, spreading over the increase is a much more accurate way of taking one month out of the year, when we know that a lot of people experience an annual increase, say, at the end of a calendar year. That is the most accurate way to reference the increase that people have experienced. […] End quote.

Bridges decides it is time to move on and asks different questions.  No explanation of a geometric mean is given.

Time for a break, and a maths lesson:

To calculate the arithmetic mean.  Add up all the values and divide the sum by the number of values. For example, if there are a set of “n” numbers, add the numbers together for example: a + b + c + d and so on. Then divide the sum by “n”.  One problem with the arithmetic mean is that its value will be influenced disproportionately by a single extreme value.

Another method is to calculate the geometric mean. To do this, multiply the values together and then, if there were ‘n’ numbers, take the ‘nth’ root. Single extreme values then have less influence.

This is exactly what Ardern’s advisers had primed her to say.

Here is a pictorial representation of the issue:

A series of twos, a few nines, a one, and a huge outlier – 90.  Arranging them in order and counting to the middle gives the median of 2, not overly useful.  Adding them and dividing by 9 gives an arithmetic mean (what most of us call ‘the average’) of 14 which is not really representative of the data either.  The geometric mean multiplies all the numbers and takes the ninth root of that and the result is 4.7 as it smooths out the large outlier of 90.

All clear?  Okay – let’s move on to Question Time on Tuesday. quote.

Hon SIMON BRIDGES (Leader of the Opposition) to the Prime Minister: Does she stand by all her Government’s statements and actions, including her statement yesterday when asked about geometric mean growth she said “when taking into account spreading over that period of time, spreading over the increase is a much more accurate way of taking one month out of the year”?

Rt Hon WINSTON PETERS (Deputy Prime Minister) on behalf of the Prime Minister: Yes. The premise of the member’s question is false and serves as proof of a poor understanding of basic facts. Her decision to try and explain that to a member needing numerical literacy was indeed a brave one. End quote.

Boom!  Quote.

Hon Simon Bridges: What did she mean when she said the geometric mean takes one month out of the year? End quote.

That is taking one part of a sentence and quoting it out of context, not very clever and Bridges really should have done a little research on geometric means before starting down this track again.  Quote.

Rt Hon WINSTON PETERS: The use of the geometric mean measurement provides an estimate of what the typical or middle household is paying in rent. It’s similar to the median in that regard, or the average in that regard. That’s what that means. End quote.

Well, that’s a bit of a broad brush fail for you too Winston, but the person in the other corner appears to be a thick as two short planks, so please continue.  Quote.

Hon Simon Bridges: Why did she say yesterday that I had selectively chosen figures which showed the median rent has increased by $30 a week under her Government, compared to $12 a week under the previous Government?

Rt Hon WINSTON PETERS: Because, unsurprisingly, the member came to this House with some false facts and thought to get them out in front of the public. Here are the real facts, though: if you go and look at, for example, 2017 rent increases, 4.8 percent; 2018, the first year of this Government, 4.8 percent; and way below the 5 percent when he was a Minister in 2015. That’s what it means.

Hon Simon Bridges: Well, wouldn’t it in fact be selective to use anything other than the total rent increase under her Government with the total rent increase under the previous Government: $30 versus $13?

Rt Hon WINSTON PETERS: It would be well-known to anyone who is literate in both this issue, statistics, as well as the law or property that for many periods you have a long, flat period in rentals, then all of a sudden you have the spike. If you measure the spike and call it an average, you’ll come up with the conclusion that member came up with in the House yesterday.

Hon Simon Bridges: Isn’t she simply overcomplicating matters with gobbledegook like “geometric mean” because she doesn’t want to face the facts of very significant rent increases in the last year due to her policies? End quote.

Just because you are too lazy to look up what a geometric mean is and come to the House properly prepared does not mean that the other person is using gobbledegook.  Quote.

Rt Hon WINSTON PETERS: I do confess that I may have made a mistake yesterday in not referring that member, the leader of the National Party, to his spokesman on statistics in this country. Then he might have been better informed, rather than come down here, drag one month, call it 12, and come up with the cock-and-bull story in terms of stats he did yesterday.[…] End quote.

Boom, boom!

Simon, you have been schooled in maths, statistics and the art of debate.

Grade F on all counts. DCM.


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WH is a pale, stale, male who does not believe all the doom and gloom climate nonsense so enjoys generating CO2 that the plants need to grow by driving his MG.

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