Lies, damn lies, statistics and MigrationWatch statistics

I'm not a statistician. I spend far less of my time thinking about statistics than I do watching films that involve a high proportion of scenes involving people kicking each other in the head, chasing each other on motorbikes and blowing stuff up. That means I've been a little slow working out what bugged me most about the MigrationWatch figures that appeared in the papers.

Here's the problem. MigrationWatch claim that estmiates of the contribution of migrants to the economy fail to address what this means in terms of GDP per head. Okay, maybe they do. I'd say that to suggest the contribution of such a small number would be loads once it's divided by sixty million is a bit silly in the first place, and I'd like to see where anyone other than MigrationWatch and the wider anti-immigration lobby say it should. But let's go along with MW for a while. We want to examine what the addition of £4bn and 185,000 people in a year does to GDP per head. How do we go about it? Probably not the MW way.

Aside from being a bit convoluted, the MW way fantastically magics away almost all of the £4bn contributed by migrants to leave only the extra bit they produce on top of everyone else, as if the remaining £3.8-odd billion never existed at all. Poof! Would the best way to work out the contribution be to ignore most of the figure? Would it really?

The rest of the £4bn does exist, and it inevitably also has an effect on GDP per head. The way to honestly calculate what that means when adding 185,000 to the population, you'd have to do something like this. Take the number of the population as a whole from 2004 - which we'll assume to be 60,000,000 (MW's assumed number). Then add 185,000 to the population to represent the net migration. There, we've increased population properly. Now divide the £4bn contributed by migrants by 60,185,000. That gives around £66.46 GDP per head (of the entire population) contributed by migrants in 2005. If you want to do the 'per week' thing because you want to make it look smaller or something, it gives you about £1.28 per head, per week. To use the Sun's methodology to express this, that's 32 TIMES the amount claimed by those completely fine, honest blokes who I wouldn't hesitate to buy a second-hand car from at MigrationWatch.

See, while those dishonest shysters fine, upstanding gentlemen claim that the government figures ignore the addition to the population, they themselves are ignoring an enormous great chunk of the contribution those people make. It'd be like having a party where everybody brought a cake, cutting a slice from one person's and throwing the rest in the bin and then shouting, 'Is that all you've brought?! One measly slice of cake?! We've got about fifty cakes here and you bring one slice?! What are you, some sort of fucking scrounger?" and then punching them in the belly. Okay, maybe not the punching in the belly bit. How about plastering articles over the press instead that say 'Person only brings one slice of cake to 'bring an entire cake' party'?