Decimal Places


Illustrating a 90% confidence interval on a st...

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Is this not the most boring topic ever? Not to me!

Which number do you trust the most:
37%
37.2%
37.24%

In the research world, decimal places are everything. One decimal place just won’t cut it, two will usually suffice, three is sometimes a delightful occurrence. Yikes! So let’s see, let’s go back to the be all and end all question in market research. “How likely are you to purchase double stuffed oreo cookies?” Let’s also say your answer can range from 0% where there’s no way you’ll ever buy that wasteful crap. Or, you can rate it as high as 100% which means I live for sugar. (And to be clear, my answer would be 98%.)

Now, let’s say I asked that question of 300 people. If memory services me correct, that’s a confidence interval of a few points. So I did my survey and I got an answer of 37%. Was that 37% or 37.2% or 37.24%? Does it REALLY matter? It’s another question of meaningful findings vs statistical significance. If my confidence interval is 3 points, does that decimal place REALLY matter? I would suggest to you that it does not.

Statistics says that 37% plus or minus 3 points includes one decimal place, two decimal places, and even, shockingly, up to infinity decimal places. So, unless your confidence interval is 0.004, stop wasting your time with decimal places and starting thinking about what really matters – MEANINGFUL numbers.

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