Much of the essay is dedicated to a summary of purportedly scientific observations supporting the law, such as the increase in the number of employees at the Colonial Office while the British Empire declined (he showed that it had its greatest number of staff when it was folded into the Foreign Office due to a lack of colonies to administer).
He noted that the number employed in a bureaucracy rose by 5–7% per year "irrespective of any variation in the amount of work (if any) to be done".
Parkinson presented the growth as a mathematical equation describing the rate at which bureaucracies expand over time, with the formula
Observing that the promotion of employees necessitated the hiring of subordinates, and that time used answering minutes requires more work; Parkinson states: "In any public administrative department not actually at war the staff increase may be expected to follow this formula" (for a given year) [1]
In a different essay included in the book, Parkinson proposed a rule about the efficiency of administrative councils.
In Parkinson's Law: The Pursuit of Progress, London: John Murray, 1958 a chapter is devoted to the basic question of what he called comitology: how committees, government cabinets, and other such bodies are created and eventually grow irrelevant (or are initially designed as such).
(The word comitology has recently been independently invented by the European Union for a different non-humorous meaning.
[11] Parkinson's conjecture that membership exceeding a number "between 19.9 and 22.4" makes a committee manifestly inefficient seems well justified by the evidence proposed[citation needed].
That it may be eight seems arguable but is not supported by observation: no contemporary government in Parkinson's data set had eight members, and only king Charles I of England had a Committee of State of that size.