LONDON — How much is a professor worth? It might help to know what professors are actually paid and how that figure compares with other salaries — and with the salaries of academics in other countries. But as Philip Altbach and his colleagues at the Center for International Higher Education discovered, such questions are a lot easier to ask than to answer.

In a new book, “Paying the Professoriate,” to be published this month, Mr. Altbach and his co-editors examine academic salaries, contracts and benefits in publicly funded universities in 28 countries. They depict a world increasingly divided “into two categories — brain drain and brain gain,” as countries with more resources siphon off academic talent from poorer countries. (In Mexico some universities are fighting back, offering faculty members a marriage bonus — for first marriages — and “two hard-cider bottles and a frozen turkey at Christmas.”) They also show a profession that in many countries is subject to a widening gap between professors at top research universities and those who work at colleges devoted mainly to teaching, “who are lower in the academic pecking order and who now constitute the large majority of the academic work force.”

All currencies were converted into U.S. dollars using a purchasing power parity index based on the cost of a set of items in the United States. But they also compared salaries in each country with that country’s average per capita gross domestic product, giving a sense of how academics were paid in comparison to pay for compatriots in other jobs. Finally each of the 28 country teams was asked whether the average academic salary for that country was “sufficient to support a middle-class standard of living.”

In terms of purchasing power, newly hired academics in China ($259 per month, as calculated by this particular study’s index) were the worst off, paid less than colleagues in Armenia ($405) or Ethiopia ($864). Academics in Canada, where the entry level salaries averaged $5,733, and full professors were paid an average of $9,485, had more cause for celebration than in the United States, where newly hired faculty members averaged $4,950 and full professors $7,358 — a figure that put the United States behind Italy ($9,118), South Africa ($9,330), Saudi Arabia ($8,524), Britain ($8,369), Malaysia ($7,864), Australia ($7,499), and India ($7,433).