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Easily calculate SUS Score


A quick tutorial to automate this task and save time

Photo by UX Indonesia on Unsplash

I've been using SUS(System Usability Scale) for a while now. It has always been a great tool to measure my designs and to help me to go on the right direction. This article is not about the SUS itself it is more a tutorial to help you to automate the calculating task. Although I'll leave bellow some very useful references about this methodology. In 4 steps I'll show how to calculate results automatically. But first some context about SUS.

The formula

The SUS survey has 10 statements and it uses a Likert Scale.The user can evaluate at witch level the statement is agreeable. So the user answers each question with a value between 1 and 5. Who is interpreting the data then have to apply a simple formula to the number. The statements that are odd you have to subtract 1. So questions 1, 3, 5, 7 and 9. For example statement 5 had was evaluated as 3, 3 –1 = 2, you'll compute 2. For the even statements, 2, 4, 6, 8, 10, you have to subtract from 5. Let's suppose that the value for the 4th statement was 3. Then we have 5–3=2, so you'll compute 2. At the end you'll have to sum all these numbers and multiply by 2.5.

This is how the formula will look like in a spreadsheet

Well it is not so hard. This is a simple formula. But what always bothered me a lot was that I had to write all this things. So I came up with a small code that do the trick by himself.

The automation

After a time thinking I found that the best way to apply this methodology is by using a digital form. I like to use Google Forms. The main reason for that is the possibility to have the results on a Google Sheets. Another advantage for this toolset is that you can use some javascript to make it even easier. So here is what I'll talk about here. But first to learn about google forms and how to make a SUS form check the video bellow.

Code to make life easier

The point in this article is not about coding. So I'll not explain what am doing with this JavaScript. But actually I'm just applying the formula I told before and calculating it automatically. But getting to the point, this tutorial will have 4 steps.

Here goes the step 1you will have to go to your Google spreadsheets under the menu tools < script editor.

Open the Script editor to add the code.
This is the editor with an starter function

Step 2

The script editor looks like any text editor that developer use. You just need to add the code bellow and click on the save button ().

Step 3

Now you just need to add the following code to the Script Editor. And again, don't forget to save the code.

Step 4

The last step is to add the function to the values your user answered. Just call the function by adding the following = sus() then add the cells were the answers are. Check the image bellow.

Conclusion

This simple code helped me a lot to analyse more responses with much less work. I'd like o thanks my friend Estacio, who helped me to get to a better version of the code. I hope this code can help you all to improve tour processes.

References to learn more about SUS:

Beyond the NPS: Measuring Perceived Usability with the SUS, NASA-TLX, and the Single Ease Question After Tasks and Usability Tests

How To Use The System Usability Scale (SUS) To Evaluate The Usability Of Your Website

MEASURING USABILITY WITH THE SYSTEM USABILITY SCALE (SUS)


Easily calculate SUS Score was originally published in UX Planet on Medium, where people are continuing the conversation by highlighting and responding to this story.