But none of my friends think… (why random sampling is important)

Sometimes the results of a survey or poll can come as a surprise. In my role I occasionally have discussions with people who doubt a result because if differs in some way from what they and their friends and colleagues believe to be true. One person recently suggested I speak with more people who have a “Labour, Green, or NZ First perspective” (as an aside, nearly all of my friends have a Labour or Green perspective).

Here’s the thing…

Nobody knows a representative group of New Zealanders.

Some might argue that they do – that their friends and colleagues are from all walks of life and are diverse in terms of their age, gender, socio-economic group, ethnicity, and location. This may all be true.

But here’s another thing…

People differ in more ways than just their age, gender, socio-economic group, ethnic group, and location.

Think of your favourite movie. One of my favourites is Crimson Tide. Are age, gender, socio-economic group, ethnic group, and location the only factors that determine the difference in our taste in movies? (Are all those things even very important in determining our taste in movies?) No – the factors contributing to our taste in movies are infinite and it would never be possible to know them all. Some factors may include our upbringing, personality characteristics, and even whether you had a submarine bath-toy as a child.

This is why random selection is vital for surveys and polls. Random selection is how researchers attempt to obtain a representative sample of people – on both the known factors (such as age, gender, and location) and the unknown factors that make people different.  A random sample helps to eliminate bias by giving all people an equal chance to be chosen (this is sometimes called a random probability sample).

Collecting a random sample is not easy – for many reasons. Obtaining a purely random and perfectly representative sample is not even possible. That is perhaps a subject for another post though…

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