Posts filed under Just look it up (278)

November 19, 2017

Hyperbole or innumeracy?

From the Herald (and also from NewstalkZB, apparently originally at South Africa’s The Citizen)

He is also said to own a custom-built Mercedes Benz s600L that is able to withstand AK-47 bullets, landmines and grenades. It also features a CD and DVD player, internet access and anti-bugging devices. The Citizen reported that Mugabe – who is a trained teacher – also owns a Rolls-Royce Phantom IV: a colonial-era British luxury car so exclusive, only 18 were ever manufactured. The vintage black car is estimated to be worth more than Zimbabwe’s entire GDP. (emphasis added)

Several people on Twitter, starting with Richard Easther, had the same reaction: that this doesn’t look remotely plausible.  It’s like the claims that Labour’s water levies would make cabbages cost $18 and a bottle of wine $75 — extraordinary claims demand, if not extraordinary evidence, at least some evidence.

So, how is it that you’d decide this number was implausible? Well, in one direction, you might try to guess the GDP of Zimbwawe.  If Zimbabwe had a smaller population than NZ you’d probably know it was a small country, so we can say there’s at least 5 million people.  So, if the per-capita GDP was only $1, it would still add up to $5 million, and that’s a very expensive car.  Since you’d expect the population to be more than 5 million and the per-capita GDP to be a lot more than $1, the figure is looking implausible.

In the other direction, you might look up the current GDP of Zimbabwe — $16 billion — or the lowest it’s been in recent years — $4.4 billion in 2008 — and note that you could by several wide-body jets for that much.

That’s enough to know something is strange. If you wanted more detail you could search for prices of Rolls-Royce Phantom IVs or of the most expensive cars ever sold, and find that, yes, there’s three or four orders of magnitude missing.

Or, you could look at the first line of the story

Zimbabwe embattled president Robert Mugabe is reportedly worth more than $1 billion despite his country being one of the poorest in the world.

Or the last line

Rolls Royce Phantoms cost a minimum of just under $698,000, but custom-built versions are sold for as much as $1.74 million. Media in South Africa reported the combined cost of the cars was about $6.98 million.

and again, there’s no way the claim about the car vs the GDP could be true — a used one couldn’t be worth thousands of times more than a new one.

So, where could it have come from?  My guess is that the claim was originally hyperbole: that someone did say “his car’s worth more than the Zimbabwe GDP” but they didn’t mean it literally. Over repetitions, the rhetorical figure turned into an “estimate”, and was quoted without any real thought.

What’s harder to understand is someone thinking a CD and DVD player is the height of motoring luxury.

October 10, 2017

Graphic of the week

From the world’s third-largest news agency:

afp

  1. The Nationalist Party?
  2. National got 56 seats, not 58 — the graph seems to have the National results from the provisional count but the Labour and Green results from the final count
  3. NZ First doesn’t use yellow
  4. ACT, on the other hand, does.
  5. But ACT is relatively unlikely to enter a left-wing coalition with Labour and the Greens
August 11, 2017

Different sorts of graphs

This bar chart from Figure.NZ was in Stuff today, with the lead

Working-age people receiving benefits are mostly in the prime of our working life – the ages of 25 to 54.

19205831

The numbers are correct, but the extent to which the graph fits the story is a bit misleading.  The main reason the two bars in the middle are higher is that they are 15-year age groups, when the first bar is a 7-year group and the last is a ten-year group.

Another way to show the data is to scale the bar widths proportional to the number of years and then scale the height so that the bar area matches the count of people. The bar height is now counts of people per year of age

benefits

This is harder to read for people who aren’t used to it, but arguably more informative. It suggests the 25-54 year groups may be the largest just because the groups are wider.

We really need population size data, since the number of people in NZ also varies by age group.  Showing the percentage receiving benefits in each age group gives a different picture again

benpop

It looks as though

  • “working age” people 25-39 and 40-54 make up a larger fraction of those receiving benefits than people 18-24 or 55-64
  • a person receiving benefits is more likely to be, say, 20 or 60 than 35 or 45.
  • the proportion of people receiving benefits increases with age

These can all be true; they’re subtly different questions. Part of the job of a statistician is to help you think about which one you wanted to ask.

August 1, 2017

Holiday travel trends

The Herald has a story and video graphic, and a nice interactive graphic on international travel by Kiwis since 1979.  The story is basically good (and even quotes a price corrected for inflation).

Here’s one frame of the video graphic
escape

First, a lot of the world isn’t coloured. There are New Zealanders who have visited say, Germany or Turkey or Egypt, even though these countries never make it into the 1-24,999 colour category. It looks as if the video picks a set of 16 countries and follows just those forward in time: we’re not told how these were picked.

Second, there’s the usual map problem of big things looking big (exacerbated by the Mercator projection). In 1999, more people went to Fiji than the US; more to Samoa than France. A map isn’t good at making these differences visually obvious, though the animation helps. And, tangentially, if you’re going to use almost a third of the map real estate on the region north of 60°, you should notice that Alaska is part of the USA.

The other, more important, issue that’s common to the whole presentation (and which I understand is being updated at the moment) is what the country data actually mean. It seems that it really is holiday data, excluding both business and visiting friends/relatives (comparing the video to this from Figure.NZ), but it’s by “country of main destination”.  If you go to more than one country, only one is counted.  That’s why the interactive shows zero Kiwis travelling to the Vatican City, and it may help explain numbers like 300 for Belgium.

Official statistics usually measure something fairly precise, but it’s not always the thing that you want them to measure.

May 22, 2017

How rich do you feel

From Scott Macleod, in a Stat of the Week nomination

The NZ Herald claims that a person earning the median NZ salary of USD $33,500 (equivalent) is the 55 millionth richest person in the world by income.

However, this must be wrong.

There are 300 million people in the USA alone, and their median income is higher than ours. This means that the average New Zealander wouldn’t even be the 55 millionth richest person in the USA, let alone the world.

Basically, yes, but it’s not quite as simple as that.  That median NZ salary looks like what you get if you multiply the NZ median “weekly personal income from salary and wages among those receiving salary and wages” (eg here) by 52, which would be appropriate for people receiving salary or wage income 52 weeks per year. The median personal income for NZ will be quite a lot lower, and the median personal income for the US is also lower: about USD30,240.

Even so, there are about 250 million adults (by the definition used) in the US, and nearly half of them have higher personal income than USD33500, so that still comes to over 100 million people. And that’s without counting Germany or the UK — or cities such as  Beijing and Shanghai that have more people with incomes that high than New Zealand does.  And that’s also assuming the web page doesn’t do currency conversions — which it looks from the code as if it’s trying to.

The CARE calculator must indeed be wrong, or using an unusual definition of income, or something. Unfortunately, the code for how it does the calculation is hidden; they say “After calculating the distribution of income, we then use a statistical model to estimate your rank.” 

As a cross-check, Pew Global also has a web page based on World Bank data.  It doesn’t let you put in your own cutpoints, but it says 7% of the world’s population had more than $50/day to live on in 2011.  The CARE web page thinks it’s more like 4.7% now.  The agreement does seem to be better at lower incomes, too — the estimates will be more accurate for people who aren’t going to use the calculator than for people who are.

 

 

May 4, 2017

Summarising a trend

Keith Ng drew my attention on Twitter to an ad from Labour saying “Under National, the number of young people not earning or learning has increased by 41%”.

When you see this sort of claim, you should usually expect two things: first, that the claim will be true in the sense that there will be two numbers that differ by 41%; second, that it will not be the most informative summary of the data in question.

If you look on Infoshare, in the Household Labour Force Survey, you can find data on NEET (not in education, employment, or training).  The number was 64100 in the fourth quarter of 2008, when Labour lost the election.  It’s now (Q1, 2017) 90800, which is, indeed, 41% higher.  Let’s represent the ad by a graph:

neet1

 

We can fill in the data points in between:
neet2
Now, the straight line doesn’t look as convincing.

Also, why are we looking at the number, when population has changed over this time period. We really should care about the rate (percentage)
neet3
Measuring in terms of rates the increase is smaller — 27%.  More importantly, though, the rate was even higher at the end of the first quarter of National’s administration than it is now.

The next thing to notice is the spikes every four quarters or so: NEET is higher in the summer and lower in the winter because of the school  year.  You might wonder if StatsNZ had produced a seasonally adjusted version, and whether it was also conveniently on Infoshare…
need4
The increase is now 17%

But for long-term comparisons of policy, you’d probably want a smoothed version that incorporates more than one quarter of data. It turns out that StatsNZ have done this, too, and it’s on Infoshare.
neet5
The increase is, again 17%. Taking out the seasonal variation, short-term variation, and sampling noise makes the underlying pattern clearer.  NEET increased dramatically in 2009, decreased, and has recently spiked. The early spike may well have been the recession, which can’t reasonably be blamed on any NZ party.  The recent increase is worrying, but thinking of it as trend over 9 years isn’t all that helpful.

May 3, 2017

A century of immigration

Given the discussions of immigration in the past weeks, I decided to look for some historical data.  Stats NZ has a report “A Century of Censuses”, with a page on ‘proportion of population born overseas.” Here’s the graph

nz-oseas-born

The proportion of immigrants has never been very low, but it fell from about 1 in 2 in the late 19th century to about 1 in 6 in the middle of the 2oth century, and has risen to about 1 in 4 now. The increase has been going on for the entire lifetime of any NZ member of Parliament; the oldest was born roughly at Peak Kiwi in the mid-1940s.

Seeing that immigrants have been a large minority of New Zealand for over a century doesn’t necessarily imply anything about modern immigration policy — Hume’s Guillotine, “no ought deducible from is,” cuts that off.  But I still think some people would find it surprising.

 

April 25, 2017

Electioneering and statistics

In New Zealand, the Government Statistician reports to the Minister of Statistics, currently Mark Mitchell.  For about a decade, the UK has had a different system, where the National Statistician reports to the UK Statistics Authority, which is responsible directly to Parliament. The system is intended to make official statistics more clearly independent of the government of the day.

An additional role of the UK Statistics Authority is as a sort of statistics ombudsman when official statistics are misused.  There’s a new letter from the Chair to the UK political parties

The UK Statistics Authority has the statutory objective to promote and safeguard the production and publication of official statistics that serve the public good.

My predecessors Sir Michael Scholar and Sir Andrew Dilnot have in the past been obliged to write publicly about the misuse of official statistics in other pre-election periods and during the EU referendum campaign. Misuse at any time damages the integrity of statistics, causes confusion and undermines trust.

I write now to ask for your support and leadership to ensure that official statistics are used throughout this General Election period and beyond, in the public interest and in accordance with the principles of the Code of Practice for Official Statistics. In particular, the statistical sources should be clear and accessible to all; any caveats or limitations in the statistics should be respected; and campaigns should not pick out single numbers that differ from the picture painted by the statistics as a whole.

I am sending identical letters to the leaders of the main political parties, with a copy to Sir Jeremy Heywood, Cabinet Secretary.

We don’t have anyone whose job it is to write that sort of letter here, but it would be nice if the political parties (and their partisans) still followed this advice.

March 8, 2017

Yes, November 19

trends

The graph is from a Google Trends search for  “International Men’s Day“.

There are two peaks. In the majority of years, the larger peak is on International Women’s Day, and the smaller peak is on the day itself.

November 26, 2016

Garbage numbers from a high-level source

The World Economic Forum (the people who run the Davos meetings) are circulating this graph:cyjjcamusaaooga

According to the graph, New Zealand is at the bottom of the OECD, with 0% waste composted or recycled.  We’ve seen this graph before, with a different colour scheme. The figure for NZ is, of course, utterly bogus.

The only figure the OECD report had on New Zealand was for landfill waste, so obviously landfill waste was 100% of that figure, and other sources were 0%.   If that’s the data you have available, NZ should just be left out of the graph — and one might have hoped the World Economic Forum had enough basic cluefulness to do so.

A more interesting question is what the denominator should be. The definition the OECD was going for was all waste sent for disposal from homes and from small businesses that used the same disposal systems as homes. That’s a reasonable compromise, but it’s not ideal. For example, it excludes composting at home. It also counts reuse and reduced use of recyclable or compostable materials as bad rather than good.

But if we’re trying to approximate the OECD definition, roughly where should NZ be?  I can’t find figures for the whole country, but there’s some relevant –if outdated — information in Chapter 3 of the Waste Assessement for the Auckland Council Waste Management Plan. If you count just kerbside recycling pickup as a fraction of kerbside recycling+waste pickup, the diversion figure is 35%. That doesn’t count composting, and it’s from 2007-8, so it’s an underestimate. Based on this, NZ is probably between USA and Australia on the graph.