The Strain Index, in its simplest form, is S3/10, where S3 is the number of syllables in three sentences. It may also be expressed in this form: 0.1 * S3. However, this easy-to-use readability formula, created by yours truly, appears to be limited by sample size. I anticipate a few Frequently Asked Questions: 1. How can I use the Strain Index if there is only one sentence, or two in the sample? 2. Can the Strain Index be applied to a full text of ‘n’ sentences?
Both these questions call for a general form of the Strain Index (SI). If ASL is the Average Syllabic Length of a sentence, then SI = 0.3 * ASL. This may also be expressed in the form 0.3 * (Sn/n), where Sn is the number of syllables in ‘n’ sentences. If ‘n’ = 3, then SI gets reduced to its simplest form 0.1 * S3 or S3/10.
Now let us apply the general formula on the first paragraph of Krishna Kumar’s ‘The Child’s Language And The Teacher’:
“Most of us are so used to defining language as a means of communication that we often forget its usefulness as a means to think, feel and react to things. This wider use of language is extremely important for people who want to work with young children, for in childhood language plays a formative role in the development of the child’s personality and abilities. It acts as a subtle, yet strong, force, shaping the child’s perception of the world, interests, capabilities, and even values and attitudes. This handbook, particularly this chapter, will explain how.”
The number of sentences ‘n’ = 4; and S4 = 149. Therefore, SI = 0.3 * (149/4) = 0.3 * 37.25 = 11.175.
It is also possible to apply the formula on just the first sentence: “Most of us are so used to defining language as a means of communication that we often forget its usefulness as a means to think, feel and react to things.” Here, ‘n’ = 1; and S1 = 42. Therefore, SI = 0.3 * (42/1) = 0.3 * 42 = 12.6.
If we choose the first three sentences, then ‘n’ = 3; and S3 = 134. Therefore, SI = 0.3 * (134/3) = 0.3 * 44.67 = 13.4. This is the same as S3/10 = 134/10 = 13.4.
Different sample sizes usually show different grades. Like most readability formulae, the Strain Index grades texts from grade 1 to 17+. It will be fine if we take more samples (three sentences each) from different parts of the book to arrive at a reliable estimate of its readability.