Public Utility Model (PUM) and System Status Management (SSM)

The technical achievement#

SSM counted calls by hour of the week and built a staffing method that followed demand, with the computing power available forty years ago, which was impressive work. Most of ODS's criticisms of it reduce to one observation: it was built without tools that are now taken for granted. The ODS positions follow from better tools, which have been available for about twenty years, and not from a quarrel.

What it got right#

The PUM showed that an average operational response time is "a statistical hiding place": a system can look fine on average while a third of a community gets almost no service. It moved the field to fractile response-time compliance. ODS keeps the insight that a single naive statistic hides failure and rejects the prescription. A fractile hides failure too: it scores a call that misses by one second and a call that misses by an hour as identically non-compliant and it buries the tail. ODS uses statistical rigor and a calibrated battery of tools, not one favored number (see Measurement & the Score).

The PUM also anticipated surrogate-shaving on quality and built guardrails against it. It required standards that were "extremely specific" and measured, vested independent clinical audit in a physician body with the power to pull certifications, and held through its performance security regime that "if you can't fire a company safely, then you can't hire that company safely." Those guardrails police clinical compliance and response-time compliance. They never measure readiness (serviceability, crew freshness), which is where surrogate-shaving on quality hides.

What eroded#

The PUM rested on conditions that have since changed. The single exclusive contractor became a single point of failure and the demand-following schedule hardened from a method into a mandate.

Two points of record. First, the claim that a contractor can increase profit solely by reducing cost applies within the PUM and nowhere else. The original text reads:

"In the Public Utility Model, the only way the ambulance service contractor can increase his profits is to find ways of meeting his production standards at lower costs. There is no other way."

Jack Stout, "The Public Utility Model, Part II: The Principal Elements," JEMS, June 1980, p. 37.

The PUM fixed revenue by design, by stripping the contractor of rate-setting and billing. It did not claim revenue is naturally fixed; for unregulated markets its author argued the opposite. Second, the well-known 1986 JEMS antitrust series, including the point that a city's contractor faces treble damages while the city faces only an injunction, was written by attorney George E. Leonard as a guest author in the same column and is Leonard's argument.

Why the fire service was alienated#

The PUM's own literature did the alienating. Its competition writings ("Please Don't Call it Competition," "Forms of Competition," the "socialized prehospital care" polemics) framed emergency transport as a contest to be won by a single selected contractor and framed publicly run and fire-based EMS as inefficient incumbents to be displaced by a competitively bid private operator. Whatever the analytic merits, the rhetoric positioned the fire service as the problem and the result was decades of turf conflict.

The deployment doctrine deepened it. Demand-chasing dynamic deployment hardened into a requirement and treated efficiency as the sole metric, pursued at the crews' expense. Much of the fire service rejects that requirement.

ODS starts from the opposite premise: every delivery model has a place and each party succeeds at what it controls.

Unit hour utilization: a cautionary tale#

There is a second lesson in this history, about metrics rather than systems, for which unit hour utilization (UHU) is the warning. UHU is a precise number that cannot answer the question the field asked of it, which is different from a good metric misapplied.

• Unactionable. UHU is an output: a ratio computed after the fact, with no lever on the other end. If a unit's UHU was 0.45 yesterday, no operational decision follows from that number today. It cannot be a target because it is a ratio, not a control.
• No demonstrated link to performance. Not in the original formulation and not in the later variants (all calls, on-scene calls only, transports only, variants accounting for task time, etc.).
• Not what people think it is. It is reported as a percent although it is not bounded at 100%: two transports in one unit hour reads 2.0. It cannot be compared across systems with different call and geography profiles.
• Weak even as a financial surrogate. As a rough guide to how many transports a system needs per hour of readiness, it rests on a stack of assumptions and direct cost and revenue analysis does the job better (Financial Sustainability).

It counts events against hours produced and a rate of events per hour says nothing about whether anything was available when the next call came.

What the field was reaching for is real and ODS uses it: concurrency measured against serviceable capacity, how often overlapping demand runs up against the units able to answer it. Concurrency is causal and actionable and it is what drives the marginal utility of unit hours (see Financial Sustainability).

The lesson is about the field rather than about SSM or the PUM: a number can look rigorous without measuring anything useful.

The record#

Two flagship PUM systems were later absorbed by fire departments: Kansas City's MAST by the Kansas City Fire Department in 2010 and Fort Worth's MedStar by the Fort Worth Fire Department in 2025. In a third, EMSA in Oklahoma, the contracted operator reached a False Claims Act settlement of roughly $20 million in 2018 (see Citations). That record contradicts the PUM's prediction that fire-based and multi-producer models would go extinct.

System design as the causal variable and the separation of authorities#

The PUM's organizing claim was that system design, not who owns the ambulances, is the primary causal variable in emergency-system performance. How a system is structured (how authority, money, information, and accountability are arranged) matters more than who employs the paramedics or whose name is on the truck.

The claim depends on what performance means. The PUM measured performance as response-time compliance. ODS measures it as readiness and response in every subsystem, which is a different quantity, so the claim does not carry over automatically. Resource availability is one of the things that drives performance and it is subject to diminishing returns: the more unit hours a system has, the less each added one contributes. Some goals are never reached by adding resources, no matter how many are added. The marginal utility of unit hours shows where a system sits (see Financial Sustainability).

In the PUM, the functions of an ambulance system are split among bodies that check one another, so no single actor can capture the system: local government sets standards and rates, an independent physician body controls clinical matters, a public ambulance authority owns assets and manages the business, and a contractor produces service. The separation was there to make a monopoly tolerable: one contractor holds the whole market, so the power around it is divided to keep it from being captured. ODS does not require a monopoly, so it needs the separation less. The anti-capture instinct is sound and ODS keeps it in a simpler form: a single body may hold several functions, provided that whenever it sets or changes the standard it is judged by, it does so explicitly and on the record (see the regulator).