The following is an excerpt of an article published in Fâneurose
But what I do find interesting is how the the Straits Times article reported on the demographic model's output based on the "net" immigration rate of 0, 30,000 or 60,000 people per annum. The numbers sound nice and pretty and round, but they blithely ignore the messy realities of life (like all models).
"All models are wrong, but some are useful." - George Box.
Let me put it this way by using an analogy.
Let's say you have a cup and you're trying to fill it with water from a running tap. You get to control how much the tap is turned and so the rate at which water drips into the cup.
Your goal is to control how fast the cup is filling up. Note, this is not the same as the rate at which water comes out of the tap. The goal is to attain a target rate for how fast the cup is filling up.
I have this magic device that can poke holes in the bottom of your cup so that water leaks from the bottom of the cup. This device can also magically seal holes in the bottom of the cup, so leakage rates can change moment to moment.
Again, let me reiterate, the goal is to achieve a target rate of how fast the cup is filling up. You only get to control the tap, not the leaks.
Oh, and lest you forget, how much water you have in your cup changes the leakage rate of water out of your cup. The pressure of a higher water level will of course force water to leak out the bottom faster.
Your job is to maintain a constant rate at which the cup is filled, whether it's 30,000 units per year or 60,000 units per year.
You also have a natural concern about how full the cup is. That's because the water is scalding hot and filling it to overflowing will burn you very badly. Oh, and your Mom will beat the crap out of you if the cup becomes too empty.
It doesn't take a genius to see that the faster the tap is flowing, the harder it is to get your job done correctly.
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