Politicisation of Statistics

I have updated my info page to reflect the fact that I am now a member of Young Nationals. Regard that information as you will.

So it’s fairly appropriate that I post about this topic. Of course, politicians of all stripes have used lies, damned lies and statistics. The whole debacle about what an “average” teacher gets paid is a fairly recent example. (I did find out what Kate Gainsford defines as an “average” teacher. I found an interview on RNZ Morning Report that she rejects the idea of an “average” teacher entirely). There have been more stories in the media about the PPTA strikes, but as usual, they lack the detail and appreciation of the context of the industrial action.

It is more than about pay but that’s what the stories centre around. On that note however, I will admit that my earlier prediction of there at least being three strikes before a circa 2.5 percent increase offer was off. It was only one strike and I don’t think the increase was as big as that.

What was rather disappointing to me was the butchering of the term “statistically significant” which has a specific meaning. But it’s not  surprising. Assisting students in understanding it is something I’ve had to do for hundreds of times as a tutor.

In question four of October 21 question time Bill English provides poor context and explanation of a statistically insignificant finding and David Cunliffe doesn’t let the technical meaning of term get in the way of trying to score political points.

Bill English said:

…The decline in median weekly income is $9, which Statistics New Zealand points out is not statistically significant. It could have dropped for any number of reasons, such as more children in the population, drops in interest rates—

A bit later David Cunliffe asked:

Does the Minister of Finance consider an income drop of $9 a week to be statistically significant to a family who, as Veda Advantage recently reported, are among the tens of thousands of New Zealanders who are finding they just cannot afford to pay their bills?

The word significance in statistics has a different meaning it has in ordinary language of meaningful or important. It relates to how strong the evidence is for making a conclusion based on the data available. In this context, there wasn’t enough evidence to conclude that there was an actual drop in the median income.

Bill English instead could have said something along the lines of Statistics NZ could not find conclusive evidence of a drop in median incomes. The reasons for a drop in his answer have nothing to do with “statistical significance”. A correct explanation in this case would have been far more suitable for him politically. He could have truthfully said “there is no evidence of a drop in median income”!

Despite lies, damned lies and statistics, Statistics NZ is a very trusted department. The Minister of Statistics in the past several years of government of both parties has been asked the fewest oral parliamentary questions. Hardly even patsy ones!

David Cunliffe outright butchers the term, using the words “statistically significant” well outside of its technical meaning, when he really meant the ordinary meaning of the word. He shouldn’t have used the $9 figure, but if he had to he should have asked whether Bill English considered “a median $9 to be unimportant” for the average family. (There’s that politically charged word “average” again…)

How…Insidious

I knew that there would be some sort of showdown between teachers and the government over National Standards. Now the stakes have been increased. There are some that are going to undermine the tests by stacking the results by “teaching to the test” on the easiest tests they can get away with.  It is a far more creative subversion that I did not anticipate.

Regardless of whether one thinks of this action there is one thing which is clear. If teachers choose to take this action it will be extremely cheap to complain that the policy failed when they openly announced they would undermine it. Especially as it was one of the current government’s election policies well signalled prior to the 2008 election.

There is only one way I can think of to get away from people fudging the numbers for league tables. Have as many key indicators as possible and apply random weightings to them. Increasing pass rates at all costs would have little effect if one year it only counted for 5% of a ranking and then 15% the next and 0% the following. Many pairs of statistics are negatively correlated as well, which makes fudging a dangerous business. You could have some adjustments ensuring that statistics that are easier to manipulate gradually reduce in weight over time.

Alternatively you could have a system where anybody can choose the key indicators that matter to them and give them the weighting that they think is best. And other people could create statistics based on what they know that others don’t think is important. Then publishing a single “official” league table would be pointless – because different people have different values. Some parents might value straight out exam results. Other parents might place value on sporting prowess. Or what they regard as “added” value once adjusted for school decile. Special character or religious ethos are important and can’t be measured by statistics – but wouldn’t it be nice if there were a system available that people could factor that in for themselves?

I think this is better than telling parents they’re too dumb to have information. Telling parents they are undermining policies that formed part of the current government’s election platform.

I disagree with sentiments that teachers have some sort of socialist agenda to indoctrinate children. And even if they did, as I have said in an earlier post, they simply don’t have the time to brainwash. Teachers are altruistic people, they care about education. There is only disagreement on the means by which it is delivered, that’s politics. During one lecture at teachers’ college, the lecturer mentioned something about making money. Some of my fellow students and I called out “we’re going to be teachers”, that is teachers don’t go into the profession to make lots of money.