In the image below, two paragraphs containing digits are presented next to each other.

First look at the left paragraph, and count all 8s.
Then look at the right paragraph, and count all 8s.

2 identical data sets beside each other, each with 5 number 8. To the left the 8's stand out more from the other digits.

Image by Karolinska Institutet University Library. Creative Commons BY-SA.

Did you manage to locate all 8s in both sets? How many were there? Did it feel equally easy in the left and the right paragraph?

Even though the data in the two paragraphs are, in fact, identical, you probably felt it was easier to find all the requested items in the left version. Why, do you think?

There are several differences in how the two paragraphs were designed.

In the left paragraph, the reader's target has another colour, and the contrast between the dark blue '8' and the light grey colour of the surrounding digits is higher (compared to the level of contrast in the right paragraph). This makes the 8s 'pop out' and easier to spot quickly.
In the right paragraph, however, all digits have the same dark colour. What separates them is merely shape. Therefore, it might take quite some time to scan through all the digits sequentially to find all 8s.

Now take a moment to reflect on the following:

Can you think of other design choices that could have made it easier for the reader to quickly identify what's important?
How might you apply this knowledge when you design graphs or other types of visualisations?