What Each Body of Research Found
On communication paths. Frederick Brooks, a computer scientist who managed IBM’s OS/360 project before founding the computer science department at the University of North Carolina at Chapel Hill, documented this dynamic directly in The Mythical Man-Month, his 1975 collection of essays on why complex projects resist simple scaling. Brooks observed that the number of communication paths required to coordinate a group of people rises not in proportion to the number of people, but roughly with the square of it — formally, as n(n−1)/2, where n is the number of people who may need to coordinate with each other. Add people to a team, and the potential coordination burden rises considerably faster than the headcount that produced it. Brooks used this to explain why adding people to an already-late project so often makes it later rather than earlier — new people require ramp-up time from existing team members, and every additional person adds disproportionately more potential coordination overhead than the last one did.
On information-processing demand. Jay Galbraith’s organisation design research, published two years earlier in Interfaces, offers a structurally similar account from a different angle. Galbraith’s argument is that the volume of information an organisation must process to coordinate its own work rises with the interdependence and uncertainty of its tasks — and that interdependence itself tends to rise as an organisation adds people and functions, because more people and functions generally means more points at which one part of the work depends on another. Galbraith’s framework does not use Brooks’s precise combinatorial formula, but the underlying shape of the argument is the same: coordination demand is a function of the relationships between people, not simply their number, and relationships grow faster than headcount does.
Where the Two Accounts Agree
Both bodies of research, arrived at independently and in different contexts — Brooks in large-scale software project management, Galbraith in general organisation design theory — converge on the same structural claim: the coordination burden inside a growing group of people is not linear in the number of people. It is closer to combinatorial, because what actually needs to be coordinated is not people individually but the relationships and interdependencies between them, and the number of potential relationships grows considerably faster than the number of people who hold them. This is a direct, well-evidenced explanation for why operational complexity so reliably outpaces headcount growth: it is not primarily a management failure or a sign of declining discipline as an organisation scales. It is close to a structural inevitability, given how coordination demand actually scales.
Where They Diverge
The two accounts diverge somewhat in what they imply is most exposed to this dynamic. Brooks’s formulation, rooted in project teams working on a shared, tightly coupled task, implies the effect is sharpest where the work genuinely requires most people to coordinate with most other people — a fully interconnected team, in his terms. Galbraith’s broader organisation-design framework implies the effect can be substantially reduced by how an organisation is structured — specifically, by reducing unnecessary interdependence between parts of the organisation that do not actually need to coordinate directly, through mechanisms such as more self-contained tasks or more deliberate information systems. Brooks’s account, in other words, treats the combinatorial growth in coordination burden as close to an inherent feature of adding people to a shared task. Galbraith’s account treats it as more sensitive to organisational design choices — implying that not every part of a growing organisation needs to experience the full force of the effect, depending on how interdependent its structure actually requires it to be.
What Remains Unresolved
Neither body of research resolves how much of this effect any specific growing organisation should expect to experience, nor does either offer a formula for managing it — and this article does not attempt to supply one, since doing so would move from evidence synthesis into the kind of prescriptive methodology outside its scope. What both bodies of evidence do establish, independently and from different starting points, is that the intuitive expectation — that complexity should scale roughly in line with headcount — is not well supported. Complexity tracks relationships and interdependence, not headcount directly, and because relationships grow disproportionately faster than the people who hold them, an organisation that scales headcount without any corresponding attention to interdependence should expect complexity to outpace growth by a wide and predictable margin — not as a symptom of poor management, but as a close-to-structural consequence of how coordination actually scales.
The scale of the effect is worth illustrating directly, because the numbers involved are easy to underestimate. Brooks’s formula implies that a fully interconnected group of five people has ten potential communication paths between its members. Double the group to ten people, and the potential paths rise to forty-five — not double, but more than four times as many. Double it again to twenty, and the figure reaches 190 — roughly nineteen times the original five-person group’s ten paths, for a group only four times its size. This is not a claim that every one of these potential paths is actually used, or that every pair of people genuinely needs to coordinate directly — Galbraith’s framework is precisely the argument that good organisational design reduces how many of these potential paths become necessary ones. But it illustrates why the felt experience of coordination difficulty rising “faster than it should” tracks a real underlying mathematical structure, rather than simply reflecting declining tolerance for complexity as an organisation grows.
There is a further implication worth stating plainly, because it runs against common intuition: this dynamic means the marginal coordination cost of each new person added to an interdependent team is not constant — it rises with every person already there. The tenth person added to a ten-person interdependent group adds considerably more potential coordination burden than the second person added to a two-person group did, even though both additions are, in headcount terms, “adding one person.” Planning and budgeting exercises that treat headcount growth as a linear cost — each new person costing roughly the same as the last — are, on this evidence, working from an assumption the underlying coordination mathematics does not actually support.
For how this pattern presents in other kinds of organisation, see other sectors.
Questions worth considering
- Where in the organisation does work genuinely require many people to coordinate directly with many others, rather than working through a smaller number of clear interfaces?
- Has headcount grown faster in areas where interdependence has also grown, or has some growth happened in more self-contained areas that carry a lighter coordination burden?
- If Brooks’s combinatorial logic is roughly right, what would that suggest about the true coordination cost of the next round of hiring, compared to the last?
This perspective is part of Operations.
Your team is facing similar challenges?
Subscribe to The Riddle Ledger
Perspectives are sent as they are published, with no promotional email, and you can unsubscribe at any time.