ITLS6201 Chap.1 Trade Flows and the Gravity Model
Trade Flows and the Gravity Model
This chapter turns the gravity model into a practical way to interrogate trade evidence. Economic size creates an opportunity for exchange, while distance, transport cost, time, tariffs, border procedures and information gaps create resistance. The important move is to treat the model as a benchmark, not a market-selection machine.
A large observed flow can be unsurprising once the size of the economies is considered, while a weak flow over a short route can reveal hidden friction. The chapter also introduces multilateral resistance: a bilateral route is judged relative to the alternatives available to buyers and sellers. Forecasting therefore needs levels, trends, a comparison set and a stated reversal condition.
What this chapter covers
- 01
Economic mass and bilateral trade opportunity
- 02
Distance and trade cost as resistance proxies
- 03
Levels, growth rates and forecast horizons
- 04
Third-country effects and multilateral resistance
- 05
Simple screening scores and their limitations
- 06
Conditional market recommendations
Worked example · free
Screen two markets without mistaking the score for a decision
- +1East's screening value is 180 ÷ 4 = 45.
- +1West's screening value is 105 ÷ 1.5 = 70.
- +1West ranks first because its lower resistance more than offsets its smaller economic size under this rule.
- +1Check product-level demand and legal market access because neither appears inside the simple index.
- +1Recommend West for deeper diligence, with East retained if its high friction can be reduced.
Key terms
- Economic mass
- The production and expenditure capacity that supports potential trade, commonly represented by measures such as GDP.
- Trade friction
- Any factor that raises the cost or difficulty of exchange, including transport, time, tariffs, procedures and information gaps.
- Gravity model
- A framework that relates bilateral trade to economic size and resistance between markets.
- Multilateral resistance
- The relative resistance created by the full set of alternative trading partners available to each market.
- Trade intensity
- The extent of trade relative to a scale measure such as output, used to distinguish absolute growth from deeper integration.
Trade Flows and the Gravity Model FAQ
Why is the gravity model useful for distribution strategy?
It supplies a disciplined benchmark. Economic size explains why some flows should be large, while resistance variables prompt investigation of distance, freight cost, time and policy barriers. The model helps identify which observation needs explanation, but a commercial recommendation still requires product demand, competitive position, legal access and service evidence.
Does a shorter route always create more trade?
No. Distance is a common proxy for trade cost, not a complete cause. A nearby market can have tariffs, weak infrastructure, restrictive access or poor demand, while a distant route can be served efficiently at scale. Compare delivered resistance and market size rather than treating kilometres as the decision.
What does a third-country effect change?
It changes the relative attractiveness of the target route. If a competing supplier becomes cheaper or a rival destination opens, the bilateral flow can weaken even though neither target country's size nor direct distance changed. State the bilateral effect first, then compare the realistic alternative route.
Exam move
Build a two-column sheet headed size and resistance. Place every case fact in one column before interpreting it. Then add a third column for alternatives, because bilateral evidence can be misleading when another supplier or buyer changes. Practise four sentence moves: describe the observed flow, explain what size would predict, identify the resistance that creates a gap, and give a conditional recommendation.
When a dataset spans several years, separate the level from the growth rate and ask whether the pattern looks cyclical or structural. Recompute simple screens without a calculator so division does not consume essay time, but spend more revision effort on the limitation. A high score is a short-list signal, not proof of profitability.
Finish each practice answer with the additional evidence you would collect and the threshold that would change the choice. Add a three-market drill in which the target route improves in absolute terms but loses relative share because a rival route improves faster. Record the observation period, units and source beside every series.
Before committing to a market, require a product-level demand indicator, a delivered-cost estimate and an access check. Use a one-way sensitivity on the friction measure and explain the result in words. This routine separates a useful benchmark from false precision and makes the final recommendation auditable. Add one final line that distinguishes the short-list decision from the later capacity commitment.
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