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Use of decimals – TMI!

November 15, 2017

In a previous blog post I said “I think non-integer percentage points are almost always unnecessary” and I thought I’d write a bit more about that.

“An integer (from the Latin integer meaning “whole”) is a number that can be written without a fractional component. For example, 21, 4, 0, and −2048 are integers, while 9.75, 5 12, and √2 are not.”

Thanks Wikipedia.

What I’m saying is that when you’re writing about research I don’t really think it is particularly useful to be so detailed and specific as to include any decimal places after your percentages.  Obviously you have that information, but there is no need to actually do anything with it.  Just round it to a whole number and move on.  Lovely.

I’ve noticed in academic research there is a tendency to present all percentages to one or two decimal places, but I’ve been ‘brought up’ in commercial research and as such I’m inclined towards simplicity of presentation.

I think that putting loads of decimal places in reports and presentations looks messy and complicated.  It clogs up my graphs and tables with text.  It makes people think there is hard maths in there.  It scares them!  It is intimidating.  And most of the time it doesn’t add anything to the interpretation of the findings.  It is information overload, too much information.

The graph on the left looks more complex than the graph on the right. No need.  The graph on the right still tells you everything you need to know but isn’t terrifying.


So it is my view that in almost all cases using decimal places is surplus to requirements.


In my line of work, I can think of a few places where I’ll stick a decimal place in:

  • When response to a question is more than 0 but less than 0.5% I would feel it was better to be specific because rounding to 0 would misleadingly imply that no-one had said that thing.
  • When rounding two questions makes response appear to be the same but it is actually sufficiently different for me to have been able to rank order them (e.g. 61.8% and 62.4% are both presented as 62%) I might add the decimal place to show my ranking logic.
  • When rounding two questions makes response appear to be the same and I know my client is going to use that information for serious decision-making I might add the decimal place to aid said decision-making.
  • I might consider adding a decimal place in for a published public opinion poll where people are likely to be really invested in the answer, particularly if the results are close.

But ONE decimal place though.  One.  Seriously.  One is enough.

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