How do Readability Indexes Work?

A readability index is a measure of how understandable your writing is to readers. Many exist. Most refer to reading ease by grade level, which as we will see is not necessarily the best guide.

Most readability formulas use some combination of five variables:

1. Tangible, or concrete, nouns.
2. Active voice verbs.
3. Word length.
4. Sentence length. 
5. Including people in your writing.

Some others also include paragraph length and number of characters. By now, all this should sound familiar to you.

Shorter words and sentences increase reading ease. Nouns that are specific, rather than abstract, are not only easier to read, they're easier to remember. Active voice verbs indicate more energy than passive voice verbs. Let's take a closer look a couple of these...

Keep sentences and paragraphs short.

We've already discussed this from a structural standpoint in Part 1. This is equally important from a "reading ease" focus.

• Avoid long sentences. They're hard to read.
• Use one major idea per sentence.
• Brevity is good for paragraphs, too.

Jakob Nielsen, in his article "How Users Read on the Web," talks about a lot of what we've covered already, and points out that...

“...Web pages have to employ scannable text, using

• • highlighted keywords (hypertext links serve as one form of highlighting; typeface variations and color are others),
  • meaningful sub-headings (not "clever" ones),
  • bulleted lists,
  • one idea per paragraph (users will skip over any additional ideas if they are not caught by the first few words in the paragraph),
  • the inverted pyramid style, starting with the conclusion, and
  • half the word count (or less) than conventional writing.”

Prefer active voice...

...as opposed to passive voice. Why?

• It's usually more specific. Passive voice tends to leave out "who" did, is doing, or is supposed to do the action.
• It conveys more "energy." Someone or something is doing (or did) something, rather than being a mere recipient.
• Passive voice evokes less trust. It's often used to avoid accountability. Consider the politicians' favorite— "Mistakes were made." 

However...

What is more important? Who did the action... or the action itself?

If who or what did the action is most important, then active voice is best. 
If the action is more important than who did it, then passive is probably just fine.