Posts from December 2012 (46)

December 4, 2012

Making Nate Silver cry

Stuff tells us

Polls have Labour closing in on Nats

A One News-Colmar Brunton poll released last night and taken a week after Labour’s leadership spat, saw the party’s vote lift 3 percentage points to 35 per cent, with the Greens up one on 13 per cent.

and later on

The One News poll of 1000 had a margin of error of 3.1 per cent.

 If you have been paying attention, you know that (a) the margin of error for a change is about 1.4 times larger than the margin of error in a single proportion, and (b) much more importantly, the useful thing to do with election polls is not to report each one separately, but to take some sort of average.

Did they have another poll? Well, the story goes on to say

 Meanwhile, a 3News-Reid Research poll, also released yesterday, showed Labour on the rise at 34.6 per cent, up 1.6 percentage points. The Greens improved 1.3 to 12.9 per cent, while National was down 1.8 at 47 per cent.

It doesn’t make as good a lead, because Labour was only up 1.6%, not 3% in this poll.  But if there are two polls, perhaps there are even more out there.

The poll of polls at pundit.co.nz shows a steady trend towards higher support for Labour, and a trend towards lower support for the Greens (with a bit more variation around the trend).  Their last update (including these two polls) put Labour up by 1% and Greens up by 0.2%.  But that would be less newsworthy.

House prices yet again

In another story bemoaning the affordability of housing outside Auckland, the Herald also tells us

The median sale price of a home in central Auckland is now $690,000 – slightly up on the previous quarter and 12.5 per cent on the 2007 boom.

That’s still down on the 2007 boom in real terms.  The story was followed the very next day by

Auckland real estate asking prices fell 2 per cent last month

The signal to noise ratio in real-estate industry press releases is not all that high.

December 3, 2012

Stat of the Week Winner: November 24 – 30 2012

Congratulations to Eva Laurenson for her excellent nomination of the NZ Herald’s article entitled “Manukau ‘luckiest’ place for Lotto”:

What does ‘luckiest’ in this title mean? Well to the average person ( I asked a few) they interpreted that title as ” I would have a higher chance of winning Lotto if I bought my ticket from a Manukau store compared to another store from a different suburb in Auckland.” Is this really the case? I doubt it. The article ranks Manukau ‘luckiest’ because it is the suburb with the highest total paid out first division amount. However no where did they take into account the total sales of Lotto tickets in each suburb. I think if you took this into account you’d see that Manukau sells alot more tickets than some of these other suburbs in Auckland. So even though Manukau can boast 55 mil in first division prizes we have no idea whether that is 55 mil out of 100 mill worth of ticket sales or 55 mil out of 1 bill worth of ticket sales. Some of the other suburbs may have a lesser amount of first division payouts compared to Manuaku but could have a greater proportion of first division payouts compared to ticket sales. Hence if that was true, your chance of winning first division given that you bought your ticket in that other suburb would be greater than (the same probability measured for) Manukau. Therefore I think there isn’t sufficient information provided to make this claim.

What I think the article could say is ‘given I won first division, the chances that I bought my ticket in Manukau are ____ times the chance that I bought it somewhere else.’ Something to this effect could be derived from the information presented by the herald article and it makes a bit of sense. Is this what the article wrote though? Not at all. They summarised this finding into “Manukau is the luckiest Lotto suburb in Auckland.” Please! This screams misleading. As discussed above, there simply isn’t enough information to justify labelling Manukau the ‘luckiest’ suburb for Lotto. People have a clear idea of what it means to be lucky and that generally is that they have an increased chance of winning. This is not the conclusion you can draw from the information they provided and in this case I believe the herald got it wrong.

I also think, although probably not the authors intentions, labelling Manukau as the ‘luckiest’ suburb has the danger of enticing people to spend more on Lotto. This article published earlier in the year by the NZ herald noted that “Many South Auckland suburbs featured among those which gambled away the most money. Mangere Bridge, Flat Bush, Manukau and Manurewa were in the top dozen suburbs.”
Even though the article was talking about the pokies, Lotto is just another form of gambling. We shouldn’t be condemming one and sending a rosy message about another, especially to communities who are struggling as it is.

Overall I think this should be the Stat of the week because using ‘lucky’ was a nice little pun but in effect mislead people regarding their chances of winning first division depending on where they bought their ticket.

Secondly it seems wrong to label a suburb ‘luckiest’ and potentially encourage a community to spend more on Lotto there when it is known that it is a compartively poorer area than other Auckland suburbs and spends alot of money on gambling as it is.

Thomas expanded on this, saying:

This looks as if it’s claiming that tickets bought in Manukau have been more likely to win. If this was true, it would still be useless, because future lotto draws are independent of past ones.

It’s even more useless because there is no denominator: not tickets sold, not people in the suburb, not even number of Lotto outlets in the suburb.

What the statistic, and the accompanying infographic, really identifies is the suburbs that lose the most money on Lotto. That’s why Manukau and Otara are ‘lucky’ and Mt Eden and Remuera are ‘unlucky’, the sort of willfully perverse misrepresentation of the role of chance that you more usually see in right-wing US outlets.

Stat of the Week Competition: December 1 – 7 2012

Each week, we would like to invite readers of Stats Chat to submit nominations for our Stat of the Week competition and be in with the chance to win an iTunes voucher.

Here’s how it works:

  • Anyone may add a comment on this post to nominate their Stat of the Week candidate before midday Friday December 7 2012.
  • Statistics can be bad, exemplary or fascinating.
  • The statistic must be in the NZ media during the period of December 1 – 7 2012 inclusive.
  • Quote the statistic, when and where it was published and tell us why it should be our Stat of the Week.

Next Monday at midday we’ll announce the winner of this week’s Stat of the Week competition, and start a new one.

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Stat of the Week Competition Discussion: December 1 – 7 2012

If you’d like to comment on or debate any of this week’s Stat of the Week nominations, please do so below!

December 2, 2012

An easy question

The Herald (quoting the Daily Mail) asksIs chocolate the new Viagra?“.

No, it isn’t. (more…)