Sample Size Calculator (and things to consider)

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Our sample size calculator is the perfect tool to let you find the perfect sample size for your surveys – without needing to getting bogged down by maths!

Here are the best practices around sample sizes and a free sample size calculator for you to use.

It will do the hard work for you!

Created by Snap Surveys – delivering excellence in survey software and experience measurement solutions since 1981.

Why should I calculate the perfect sample size?

Calculating the perfect sample size is a way to save time and money by interviewing fewer people, without compromising the accuracy of your results.

For example, if a large supermarket chain is looking for feedback on the shopping experience they offer, they can invite customers to answer a survey.

But do they want to invest in surveying customers in every store around the country? That requires a lot of time, effort and money because of the scale of the operation.

There may be postage costs for paper surveys, you may be offering an incentive to customers to complete the questionnaire, or maybe you’re using an offline interviewer tool.

 Instead, they can just select a small group of stores to run the survey. The amount of responses they receive will be the sample size, and can be used to represent the views of the entire customer base.

But how many responses do you need for a true representation of all the customers?

Below are the four important considerations for determining the perfect sample size.

What makes a perfect sample size?

To find out the perfect sample size for your survey, you need to know a few other things first.

  • Population size (overall)

How many people will your survey represent? In our earlier example, the supermarket chain would consider their estimate of total customers around the country.

  • Margin for error

How likely are your results to reflect the views of the wider population? By calculating your margin for error, you can use it to establish a percentage range for how accurate your results may be – such as between 68% and 72%.

Check out our margin for error calculator.

  • Sampling confidence level

This is a percentage that tells you how confident you are that your sample results can be achieved consistently. If you ran the survey 100 times, how many times would the answers fall within the margin of error? If this would occur 90 times out of 100, then your sampling confidence level is 90%.

  • Response rate

How many participants will fill in your survey to completion? Sometimes requests get ignored or surveys only get partially completed. A good response rate is a key component to quality data that allows you to see the bigger picture.

Weighting your sample size

Survey data weighting – when referring to respondents – is a way of correcting issues in the demographics of those who respond to a survey.

For example, if a theme park is running a visitor survey, a representation sample of visitors is interviewed. The theme park will be able to identify the total number of visitors that day through ticket sales.

To weight their sample size, they just need to factor up to the total number of daily visitors. If 1,000 visitors were interviewed, and the total daily visitors was 10,000, then each visitor counts for 10 people.

It should be noted that there will likely be different profiles of visitors on different days of the week, so this will also need to be taken into account.

Increasing the value of certain responses helps to ensure your sample size data reflects the overall population.

Find the middle ground

Larger sample sizes = time and money

You don’t always need a large sample size.

While a bigger sample size lets you increase your confidence level or reduce the margin of error, it also means you need to survey more people. This can require more resources.

If time, money or manpower is of the essence, consider whether a smaller sample size is viable – perhaps in a more targeted way.

TIP: Using an experience measurement platform is a great way to make the process as smooth as possible. Snap XMP lets you share surveys via any channel or device, which comes in handy when your sample size needs to be bigger.

Learn more about Snap XMP.

Small samples can be misleading

As we’ve said, sample sizes that are too small (or ones without the wider context taken into account) can provide misleading answers.

 It’s important you get it right.

So what’s the middle ground?

Our calculator will help you find it! Scroll back up to use it.

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