In this post we explain what people mean when they refer to the ‘margin of error’ in a survey and share a margin of error calculator which you can use to estimate survey reliability.

There are four important words in the world of B2B research:

  • The ‘population’ is the entire group of people that you’re interested in, e.g. your target market, your customers
  • A ‘census’ means that you’ve measured the views of every single person in the population
  • A ‘survey’ means that you’ve measured the views of some, but not all members of the population (you’ve taken a ‘sample’)

A census is great as it gives you a definitive answer to your question – because every single person of interest has inputted, you can have great confidence in the results.  However, conducting a census is usually impractical because the population may be large (thus consulting everyone in it time consuming and costly) and not everyone in it can actually be engaged. 

That’s where surveys come in.  They’re practical to conduct and give an indication of what you’d be likely to find in the wider population.  But how good an indication of wider opinion does a survey give?  To estimate this, we use a statistical concept called the ‘margin of error’

The margin of error tells you the extent to which a survey result is likely to match what you’d see in a census.  For example, imagine that 50% of people answer ‘yes’ to a survey question and the margin of error is +/-3%.  This means that the survey result is likely to differ from the result you’d see from the entire population by no more than +3% or -3% (i.e. a census would see a result between 47% and 53%).  The margin of error needs to be considered in conjunction with the ‘confidence level’ which indicates how often the margin of error (which is after all an estimate) will be accurate.  For example, a confidence level of 95% (a common standard used in research) means that the margin of error will hold true in 95 out of 100 cases.

You can use the calculators below to calculate the margin of error.  The first can be used when planning a survey to see what margin of error different sample sizes would bring.  The second can be used post-survey to see the precise margin of error for a particular result.

Predict the margin of error before your survey


Sample size must be greater than 0
Min Max
 

Calculate the margin of error for a result in your survey


Sample size must be greater than 0
Min Max
%
Confidence must be a percentage between 1 and 99
 

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About Andrew

Andrew has specialised in B2B research for over a decade and co-founded Circle Research in 2006. He is a columnist for B2B Marketing Magazine, a regular contributor to Research Live and frequent speaker at leading events such as the B2B Leaders Forum, Customer Experience Live and the Social Media World Forum. Andrew is a Chartered Member of the MRS, teaches the MRS B2B research course and holds an MA in Psychology from Aberdeen University alongside an MSc in Marketing from Strathclyde University.

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