Tuesday 20 November 2007

Let’s take a random sample and see

Why do you want to take a random sample? An engineer makes his entire plan on a computer first, and subjects it to every sort of test, even when each element in it has known properties. He makes scale models, and makes corrections and tests every step of the way, till he’s absolutely sure. Then puts the structure into use very gradually. Ditto for pharmaceuticals. Yet direct marketing must hold up to testing on a random sample!

When any idiot will tell you that a test on a random sample is bound to fail, because most people in the list are bound to say No. For starters, many will never buy what you are selling. And even the ones who will are very unlikely to all be in the market exactly when you’re testing.

Which means even if a section gave a ‘thumbs up’ to the test, it’s bound to be swamped by the overall and overwhelming failure that permeates through the list as a whole?

Does that mean we shouldn’t take random samples? Of course, we should. But after understanding what the term means. We should take a random sample of those sections which we think are most likely to form the market; take enough from each of these to yield dependable numbers; and a random sample of the balance, to see how well your selection works out in real life.

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