How to call bullshit on statistics. e.g 2

This article has got a lot of press coverage as well. It contains a startling claim:

Goodall says, "our total use of materials [in 2007] was almost the same as it was in 1989, despite the economy having tripled in size in the intervening years

This falls into the A Second's Thought Should Tell You It's Wrong category.

A tripling of the economy in the years from 1989 to 2007 would require a growth rate on average of 3^(1/18)-1 which equals 6.4% per year, every year. I'm not going to look up the data, but I'm pretty confident the UK hasn't grown that fast in a year in the past 30 (and hardly ever - perhaps the Barber boom peak?). In fact between those years UK GDP rose by 59%, a rate of 2.6%.

So what does he mean? I know where the figure comes from - it is true that UK nominal GDP rose by 3 times between 1989 and 2007. Clearly this was mostly inflation, ie a rise in prices. There's no reason why a rise in prices should require more 'stuff', and of course to use such a figure is completely wrong.

To be fair to the academic, it might be a journalistic or sub-editing error as the original paper doesn't contain the statistic.

How to call bulls**t on statistics. e.g 1

I'm good at spotting dodgy statistics, and I thought it might help me and others in listing the ways you can spot them (which I'll do as they occur to me.

This has been doing the rounds:

A couple of years ago, there were more [Porsche] Cayennes circulating in Greece than individuals who declared and paid taxes on an annual income of more than €50,000, a figure only slightly above the vehicle’s list price

.

Now, what rings the alarm bells here? It's not the source, which seems respectable enough. It's also not the overall feel of it, as we know Greece has a problem with richer taxpayers declaring income. It's not even the slightly odd comparison of a stock (Cayennes in Greece) with a flow (income per year). There is the niggling concern that this allows us to laugh at foreigners, but the author is a foreigner so we'll let that pass.

No, what makes it require further checking is the specificity of it. For unless Cayennes' have an extremely high market share of the luxury sector, which would in itself be unusual*, if there are more Cayennes in Greece than €50,000/year taxpayers, there must be loads more other luxury cars: Porsches, Ferraris, Mercedes, BMWs, and so on. So why not say that to make the point about tax evasion?

So let's do some checking. We find there are statistics on Greek Cayenne sales. For example in 2005 there were 278 sold. In 2007 265.

In total since its launch in 2003 (in Greece, 2002 worldwide) a rough (I've not used a calculator) figure is about 1,700 sales. This is less than 0.1% of the market in this period, I think, possibly less than their UK share (but I can't find figures for those).

So on the face of it, unless there are exceptionally few taxpayers over €50k**, the statistic looks false (and if there are, why use Cayennes as your comparison?). There might of course be factors I do not know about - secondhand imports, non-official sales, or maybe I've made a mistake. After all the author of the piece is Greek. But it was the Cayenne bit that seemed wrong.

* Also Greece is surely hilly, and in places will have bad roads, so the idea of buying a Cayenne is not as ludicrous as the author suggests. But then again he is from the country.
** Of course this is the other way to look at it, how many taxpayers are there? I could only find statistics of 5,000 over €100,000, which is obviously a low figure but more than the Cayennes. And there would be many times (10? 20?) more taxpayers over €50,000 than €100,000.
Nb: Author also mentions a certain town, the region of which it is in reported only a handful of Cayenne sales in those years.

Govt deficts do not equal country deficits

The BBC reports:

1450: BBC's Mark Gregory has been looking at the economic impact of the quake. Early estimates have put the cost at £112bn ($180bn), equal to 3% of national output. "That's a large burden for a nation that even before last week's disaster had the highest public debt - 200% of GDP - of any advanced economy," he says.

Well not really. It does mean rebuilding will be quite a burden for the Japanese government, which is heavily indebted. But almost all of the debt is owned by Japanese households, and then some - the net external assets of Japan are something like $3 trillion, about 55% of Japan's GDP.

So the amount to spend on reconstruction should not really be seen in the context of the government's deficit, but the assets of the country, its GDP and also its claim on foreigners. All of which are huge.

Stamps as an investment

In the UK since 1989 you have been able to buy a stamp that is simply called '1st' for 1st class post. These are known as 'forever stamps', (or the rather boring Non Value Indicator (NVI)) as they will forever pay for 1st class postage. The price of one of those 1st class stamps has risen from 20p to this year's (from April) 46p, a rise of 130% (inflation has been 75% on the CPI over that period).

So would it have been a good idea to buy those stamps in 1989 and hold them until today? The above chart shows the value of a 20p put into a bank account (or £20 or £20m etc) and the same amount of 1989 'forever' 1st class stamps. It's true the bank account would have done better, returning 61p today, enough to buy nearly 1.3 1st class stamps. However if you take off 20% income tax then the amount is very similar.

Furthermore stamps have clearly done better over the last few years.
This chart starts at 2005, and show stamps have outpaced even pre-tax bank accounts.

Stamps have other advantages. They are backed by the British government in a way - certainly there wasn't a run on them in 2008. They don't count against means tested benefits. They might (I've not checked) be good diversifiers.

Of course there are drawbacks. Stamps are not the most liquid of assets. You can use them, but you might not place 46p of value on them, or you can sell them (the Post Office won't buy them back). An auction just ending on Ebay is fetching 40p a stamp, a discount of nearly 2.5% on the current 41p price (for another month). Others show a larger discount. Stamps are quite bulky if you want to invest a lot.

A more major issue might be what you are buying. In a world of Twitter and email and so on one might think the value of posting a letter will not keep up with prices. That it has so far is no proof it will in the future. Another problem is default - the Royal Mail might go bust. More common is a change in the contractual terms - e.g. a restriction in what the stamp buys. In fact this happened on 21st August 2006 when the Royal Mail introduced a size limit on 1st class post - 240mm by 165mm by 5mm. However it also increased the weight limit from 60g to 100g. This makes comparing pre-2006 to post-2006 data difficult.

Maybe it would be easier to speculate. Buy up a lot at the current price of 41p, then sell them in April for a small discount on the 46p new price.