science

Tobin's q

Tobin's q 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 Tobin's q rather than just read about it. In short: Tobin's q (or the q ratio, and Marris's v), is the ratio between a physical asset's market value and its replacement cost. It was first introduced by Robin Marris as a firm-level microeconomic variable in his 1964 book The Economic Theory of Managerial Capitalism, and was shortly afterwards further analysed by Richard Kahn in early drafts of his paper Notes on the Rate of Interest and the Growth of Firms (not publis…

Key takeaways

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

Reference excerpt

Tobin's q (or the q ratio, and Marris's v), is the ratio between a physical asset's market value and its replacement cost. It was first introduced by Robin Marris as a firm-level microeconomic variable in his 1964 book The Economic Theory of Managerial Capitalism, and was shortly afterwards further analysed by Richard Kahn in early drafts of his paper Notes on the Rate of Interest and the Growth of Firms (not published until 1972). Nicholas Kaldor in 1966, without acknowledgement to his Cambridge colleagues Marris and Kahn, repurposed the valuation ratio as a macroeconomic variable in his paper: Marginal Productivity and the Macro-Economic Theories of Distribution: Comment on Samuelson and Modigliani. It was popularised a decade later by James Tobin, who in 1970, described its two quantities as:

One, the numerator, is the market valuation: the going price in the market for exchanging existing assets. The other, the denominator, is the replacement or reproduction cost: the price in the market for newly produced commodities. We believe that this ratio has considerable macroeconomic significance and usefulness, as the nexus between financial markets and markets for goods and services.

Measurement

Single company Although it is not the direct equivalent of Tobin's q, it has become common practice in the finance literature to calculate the ratio by comparing the market value of a company's equity and liabilities with its corresponding book values, as the replacement values of a company's assets is hard to estimate:

Tobin's q = (Equity Market Value + Liabilities Market Value) (Equity Book Value + Liabilities Book Value) {\displaystyle {\frac {\text{(Equity Market Value + Liabilities Market Value)}}{\text{(Equity Book Value + Liabilities Book Value)}}}}

It is also common practice to assume equivalence of the liabilities market and book value, yielding:

Tobin's q = (Equity Market Value + Liabilities Book Value) (Equity Book Value + Liabilities Book Value) {\displaystyle {\frac {\text{(Equity Market Value + Liabilities Book Value)}}{\text{(Equity Book Value + Liabilities Book Value)}}}} . Even if market and book value of liabilities are assumed to be equal, this is not equal to the "Market to Book Ratio" or "Price to Book Ratio", used in financial analysis. The latter ratio is only calculated for equity values: Market to Book Ratio= Equity Market Value Equity Book Value {\displaystyle {\frac {\text{Equity Market Value}}{\text{Equity Book Value}}}} . Financial analysis also often uses the inverse of this ratio, the "Book to Market Ratio", i.e. Book to Market Ratio= Equity Book Value Equity Market Value {\displaystyle {\frac {\text{Equity Book Value}}{\text{Equity Market Value}}}}

For stock-listed companies, the market value of equity or market capitalization is often quoted in financial databases. It can be calculated for a specific point in time by number of shares × share price {\displaystyle {\text{number of shares}}\times {\text{share price}}} .

Aggregate corporations Another use for q is to determine the valuation of the whole market in ratio to the aggregate corporate assets. The formula for this is: q = value of stock market corporate net worth {\displaystyle q={\frac {\text{value of stock market}}{\text{corporate net worth}}}}

The following graph is an example of Tobin's q for all U.S. corporations. The line shows the ratio of the US stock market value to US net assets at replacement cost since 1900.

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Tobin's q

Start with the simplest possible case. Write down what Tobin's q 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 Tobin's q 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 Tobin's q 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 Tobin's q

In research: Tobin's q 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 Tobin's q 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: Tobin's q is common in secondary-school and first-year university syllabi. It links to neighbouring topics Financial ratios, Valuation (finance), so understanding it makes those chapters shorter.
In everyday life: Look for Tobin's q 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 Tobin's q in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Tobin's q 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 Tobin's q out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Tobin's q in simple terms?

Why does Tobin's q 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 Tobin's q?

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 Tobin's q.