'Readability' refers to the level of difficulty of text and it is measured using specific tools and formulas. Drs. Arocha and Hoffman-Goetz use these tools to evaluate the complexity of information available on popular websites.

It's one thing to be able to read words. It's another to be able to understand the meaning of these words.

'Comprehensibility' refers to an individual's capability to understand information. The researchers evaluate this through standardized tools and one-on-one interviews with participants, which test the individual's ability to recall and explain concepts they've just read.

In order to demonstrate the differences between readability levels, here is an example of a sentence at:

(a) Grade 11 reading level:

Sometimes the preliminary test results are positive when the person is not infected. A positive AIDS test should be reconfirmed by a different lab technique to assure that it is accurate.

(b) Grade 6 reading level:

If your AIDS test comes back positive, you may not have AIDS. Have the test done again using another method. Sometimes the first lab test gives a false reading.

As you can see, both sentences express the same idea, but the level of comprehension needed to understand the meaning of each sentence varies according to the language used and the writing style.