science

SMOG

SMOG is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand SMOG rather than just read about it. In short: The SMOG grade is a measure of readability that estimates the years of education needed to understand a piece of writing. SMOG is an acronym for "Simple Measure of Gobbledygook".

Key takeaways

SMOG belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect SMOG to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of SMOG from memory before moving on to harder problems.

Reference excerpt

The SMOG grade is a measure of readability that estimates the years of education needed to understand a piece of writing. SMOG is an acronym for "Simple Measure of Gobbledygook". SMOG is widely used, particularly for checking health messages. The SMOG grade yields a 0.985 correlation with a standard error of 1.5159 grades with the grades of readers who had 100% comprehension of test materials. The formula for calculating the SMOG grade was developed by G. Harry McLaughlin as a more accurate and more easily calculated substitute for the Gunning fog index and published in 1969. To make calculating a text's readability as simple as possible an approximate formula was also given — count the words of three or more syllables in three 10-sentence samples, estimate the count's square root (from the nearest perfect square), and add 3. A 2010 study published in the Journal of the Royal College of Physicians of Edinburgh stated that “SMOG should be the preferred measure of readability when evaluating consumer-oriented healthcare material.” The study found that “The Flesch-Kincaid formula significantly underestimated reading difficulty compared with the gold standard SMOG formula.” Applying SMOG to other languages lacks statistical validity.

Formulae To calculate SMOG Index

Take three ten-sentence-long samples from the text in question. In those sentences, count the polysyllables (words of 3 or more syllables). Calculate using

grade = 1.0430 number of polysyllables × 30 number of sentences + 3.1291 {\displaystyle {\mbox{grade}}=1.0430{\sqrt {{\mbox{number of polysyllables}}\times {30 \over {\mbox{number of sentences}}}}}+3.1291}

This version (sometimes called the SMOG Index) is more easily used for mental math:

Count the number of polysyllabic words in three samples of ten sentences each. Take the square root of the nearest perfect square Add 3 SMOG conversion tables compiled by Harold C. McGraw are slightly inaccurate because they are based on the approximate formula. Furthermore, tables for texts of fewer than 30 sentences are statistically invalid, because the formula was normed on 30-sentence samples.

References

Worked examples

Example 1 — a first encounter with SMOG

Start with the simplest possible case. Write down what SMOG claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to SMOG before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about SMOG ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of SMOG

In research: SMOG appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses SMOG in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: SMOG is common in secondary-school and first-year university syllabi. It links to neighbouring topics Readability, so understanding it makes those chapters shorter.
In everyday life: Look for SMOG outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study SMOG in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what SMOG means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain SMOG out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is SMOG in simple terms?

The SMOG grade is a measure of readability that estimates the years of education needed to understand a piece of writing. SMOG is an acronym for "Simple Measure of Gobbledygook".

Why does SMOG matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study SMOG?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on SMOG.