External and supply dependencies

United States · observed starting scales, conditional stress paths

Stocks buy time while supply flows are interrupted

An economy can keep producing during a disruption if the right inputs are in stock or substitutes arrive soon enough. Total inventories help establish scale, but only product-level dependencies reveal which missing item stops production.

Country, period and measurement

Interactive macro mechanism · no recession probability

Watch pressure accumulate over time

1. Month 0
   A measured US inventory and sales scale.
2. Disruption begins
   New deliveries fall; stored goods fill part of demand.
3. Lead time expires
   Partial replacement flow arrives if disruption continues.
4. Recovery
   Extra deliveries rebuild stocks; previously lost activity is not automatically recovered.

Starting inventory is $2,012.743 billion and starting monthly sales are $1,464.205 billion. Under the declared value bridge, 6 disrupted months leave $1940.6 billion of cumulative sales-equivalent demand unfilled. Replacement covers half the missing flow only after 3 complete months, while the disruption continues. The lowest assumed activity / staffing index is 57.5; this is not a measured U.S. employment outcome.

How this becomes a macroeconomic vulnerability

Supplied, stored and missing add to demand

The stacked allocation separates new deliveries used, inventory drawn and demand left unfilled. Every month closes an inventory account: ending stock = beginning stock + additions − withdrawals. Sales forgone are cumulative; they do not vanish merely because supply recovers.

A delay is a period with no replacement flow

A three-month lead means no substitute deliveries in months 1–3; the first possible arrival is month 4, if disruption is still occurring. This lesson assumes replacements cover half the missing flow. Moving the delay slider reveals whether inventories last long enough.

Why aggregate inventory is not a national resilience score

Oil, chips, food and medicines are not interchangeable. One critical component can halt a whole process even when other warehouses are full. This exercise deliberately assumes a one-dollar inventory-to-sales bridge to teach stock and flow arithmetic. It does not infer physical production or usable days from a nominal ratio.

What a country model must add

A national calculation needs industry input-output coefficients, domestic and foreign supplier shares, route capacity, inventories by input, substitution costs and lead times. Avoid adding gross supply-chain sales to GDP: intermediate transactions can be counted several times. Fiscal support can sustain demand but cannot instantly manufacture an unavailable component.

Could a missing input or route interrupt production?

Production depends on usable inputs arriving when needed. A disruption matters most when an input is essential, inventory is limited and a qualified replacement cannot arrive quickly. Dependence can be domestic or foreign. Several suppliers help only if their products are usable and they do not share the same vulnerable location or route.

1. An essential input or delivery route becomes unavailable.
2. Inventory and usable replacement supplies cover part of the requirement.
3. The remaining input shortfall constrains production under the process's actual technology.

Synthetic teaching example · not a forecast

How far do five days of inventory go?

Synthetic one-input production process. Normal input use is one unit per day. The original supplier stops completely for the chosen number of days. Qualified replacement supply starts immediately at a fixed share of normal daily use, and inventory covers the remaining need until exhausted. Each unit of input supports one unit of output; no recovery backlog is modeled.

Uncovered input: 11 equivalent full-rate days. Replacement supplies 4 input-days and inventory supplies 5 once, against 20 required. Output is reduced during 13.75 calendar days; the total shortfall equals 11 full production-days only under this one-input, proportional-output assumption.

Evidence to watch

Keep each observation’s definition, date and reporting frequency. A daily page refresh does not create new daily balance-sheet data.

What this example leaves out

• All inputs are synthetic. Equivalent full-rate input-days measure a quantity shortfall, not necessarily the same number of calendar days with a complete shutdown.
• Replacement is assumed immediately available and fully usable. Real substitution can require qualification, transport, scarce capacity or redesign; prices and restart costs are absent here.
• Production responds proportionally to one input. Indivisible processes, several simultaneous shortages and catch-up production require a different model.
• An observed assessment needs product and process detail, usable inventories, lead times and shared dependencies. Import value, supplier count and freight costs alone do not establish current fragility or disruption probability.

These mechanisms can overlap. Adding their example outputs does not produce an overall fragility score or a recession probability.

Further mechanism sources

• OECD Supply Chain Resilience Review (2025)
• OECD review: inventory, supplier compatibility and risk-management trade-offs (full report PDF)

Observed US starting values and their dates are attributed above. The smaller example uses authored numbers; all stress paths retain their own stated assumptions.

Explore the other dimensions

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