The usual gauge for readability is Reading Grade Level (RGL). A host of readability formulas have been developed since the first was created early in the last century. Common readability formulas include the Flesch, Flesch-Kincaid, and Forecast. All of them assess reading difficulty using factors such as sentence length and number of syllables, and all relate the difficulty of reading material to the abilities of typical readers at each grade level. Readability formulas can be useful in identifying text which uses involved sentence structure and difficult vocabulary, but they are crude tools and require a lot of judgement and common sense.

When the literacy task is to search text for specific information, the organization of the text is of primary importance. Text that is organized by topic and marked with headings can be searched more effectively than continuous passages. Well-written, single topic paragraphs are easier to scan for information than paragraphs with no topic sentences and unconnected ideas. Information about the organization of text passages is not captured using readability formulas and reading grade level.

Document Complexity

‘Reading grade level’ is also a poor way to describe the complexity of documents where text is discontinuous or where graphic elements carry much of the meaning. Finding a location on a city map may require some reading of place names, but the overall task depends more upon the ability to use the index and locator grid for the map to find locations and routes. Likewise, it is difficult to talk about the ‘readability’ of a graph, table or scale drawing which displays only half a dozen words.

One way to estimate the complexity of documents is to count the number of ‘organizing categories’ and the ‘specific items’ subsumed under each category. The greater the number of organizing categories and the greater the number of specific pieces of information identified in each category, the more complex the document.

If one ignores all the front matter–how to contact the phone company, how to dial direct, what to do in a meteor shower, etc.–the white pages of the typical phone directory is a list of subscribers, all of whom appear in the one ‘organizing category’ combined with a list of phone numbers, all of which appear in another organizing category. The white pages may have thousands of specific items or instances underneath these labels, so a random search is ineffective, and it must be searched alphabetically. The given information for a search of the phone book is limited to one or two search terms–last name, initial, address–and usually yields only one number. Using the white pages in the usual way is a fairly simple task.

On the other hand, the Yellow Pages is a much more complex document in which the subscriber list is nested into perhaps a thousand organizing categories, each with many entries or specifics under each. Locating any specific entry involves finding, or inferring the correct category, and then matching criteria for requested information, as for example, a bookstore which is open on Sundays.