You can use the same readability formula to measure any text for any reader for any purpose. The formulas focus narrowly on counting attributes of individual words and sentences. This generic approach to measure difficulty of a text implies that readers process information in a uniform and passive way, word by word, sentence by sentence. But people are not passive text-processing machines. We all approach reading in an active way. We search for meaning and we bring our attitudes, interests, knowledge, and experiences to bear on what we read.
Thinking about the active role of the reader helps put readability formulas in perspective. While the formulas typically assume that longer words are less familiar and harder to read than shorter ones, we can find many exceptions to this rule.
For example, the reader's familiarity with the subject matter counts for a lot. The two examples below illustrates the point that not all content with the same readability score is equally easy to understand.
Both examples have short sentences and mostly short words, and the some readability score. But which example is easier to understand and do?
1) Write down your first name.
2) Now put down your middle initial and your last name.
3) Fill in your age on the next line.
1) Enter your gross annual income.
2) Add all your assets in real estate, stocks, and bonds.
3) Figure your tax from the table.
A grade level score does not tell you if the material will attract and hold your readers' attention. Nor does it tell you if your readers will find the material culturally appropriate, or if they can understand and use your material as it is intended.
Readability formulas cannot tell you if written materials are clear and effective to the target readership.
1) Your document might impress upon the reader that your document is going to be hard to read.
EXAMPLES: hard to skim; an overpowering "wall of text;" hard to read due to small print or poor contrast; the layout looks too busy or confusing or complicated.
2) Readers may find your material too hard to follow or understand.
EXAMPLES: it uses words the reader doesn't know; it's poorly organized; doesn't explain things well or lacks cohesion; the design is distracting rather than helpful.
3) The reader might not be able to focus on it.
EXAMPLES: the reader is in a hurry or distracted; the reader's literacy skills and concentration are suffering due to stress.
4) It might not attract and hold the reader's interest
EXAMPLES: The reader doesn't notice it; the reader notices but doesn't find it interesting or appealing at first glance; the reader begins reading it and then loses interest.
5) It might be culturally unsuitable for the reader.
EXAMPLES: the reader can't relate to it; doesn't feel respected and understood; feels put off or is offended by it.
6) Your material's purpose or usefulness might be unclear or unappealing to the reader.
EXAMPLES: the reader can't figure out what it's for or how to use it; sees no benefits from reading it; finds the action it calls for too difficult or unrealistic.
Remember: The reader is the one who decides what is worth reading. It's also the readernot a grade level scorewho decides if the material is easy to understand and use.
The difficulty of words and sentences is one of many factors that contribute to making materials clear and effective. This means that using a grade level score as the only criterion or summary indicator can mislead you into thinking that you have written materials which readers will find suitable and effective, when, in fact, readers cannot understand what you have written. Keeping individual words and sentences easy enough for your readers is necessary but not sufficient to ensure readers can understand and use your material.