When Correlation Does Equal Causation

There is a particular sentence you are not supposed to say in polite public health circles:

Sometimes, correlation does equal causation.

For years, governments have raised cigarette taxes under the banner of deterrence. The logic is simple and intuitively appealing: make smoking more expensive, and fewer people will smoke. Price is a lever. Pull it hard enough and behaviour changes. In many contexts, that has proven true. Official sales decline. Surveyed prevalence falls. Treasury revenues initially increase.

But in a growing number of countries, something else rises alongside the tax curve.

The black market.

This isn’t conjecture. It isn’t an industry press release. It is visible in customs seizure data, enforcement taskforces, budget allocations for illicit trade units, widening price gaps between legal and illegal products, and the lived reality of cities where illicit tobacco is no longer hidden but openly traded.

And yet, prominent tobacco control academics such as Becky Freeman and Simon Chapman continue to argue that there is “no evidence” that high tobacco taxes cause illicit trade. In this framing, illicit markets are purely the work of organised crime and weak enforcement. Criminality is the cause; tax policy is incidental.

But markets do not operate in moral categories. They operate in incentive structures.

Australia ratified the WHO Framework Convention on Tobacco Control in 2004 and has been one of its most enthusiastic implementers. Article 6 of the treaty explicitly encourages price and tax measures as a central demand-reduction strategy. Over the past decade, Australia has repeatedly increased tobacco excise, on top of automatic biannual indexation. The result is that a legal pack of cigarettes now exceeds AUD $50 in many parts of the country.

Simultaneously, Australia has seen a documented expansion of illicit tobacco. “Chop chop”, loose-leaf tobacco is widely available. Counterfeit branded packs circulate through informal retail networks. Border Force reports significant seizures. State authorities have acknowledged billions in lost excise revenue. There have even been reports of violent competition over illicit distribution territories.

Are we meant to believe this is unrelated?

The United Kingdom, also an early FCTC ratifier, has long operated a tobacco duty escalator. Cigarette prices are among the highest in Europe. At the same time, enforcement agencies continue to report counterfeit production sites, smuggling through ports, and significant illicit market share in certain regions. Large price differentials between the UK and neighbouring countries create powerful incentives for cross-border purchasing and organised supply chains.

In France, another FCTC Party, cigarette prices have climbed steadily and now rank among the highest in continental Europe. France also consistently appears near the top of European illicit consumption estimates. Cross-border flows from lower-priced neighbouring jurisdictions are common. Again, the mechanism is not mysterious.

South Africa provides perhaps the clearest natural experiment. Long-term excise increases were followed by a complete sales ban during COVID-19 restrictions. Legal supply disappeared overnight. Demand did not. Illicit trade surged dramatically during the ban and remains elevated years later. Once informal distribution networks are established and consumers become accustomed to them, they do not simply evaporate when formal sales resume.

The FCTC now has more than 180 Parties. The overwhelming majority of countries facing significant illicit tobacco challenges are signatories operating within the same global policy architecture that promotes sustained tax escalation. To be fair, the FCTC also includes a Protocol to Eliminate Illicit Trade in Tobacco Products. Enforcement cooperation, tracking and tracing, and supply chain controls are part of the framework.

But enforcement does not repeal economics.

If the legal price of a product is driven far above its marginal production cost through taxation, the spread between legal retail price and black-market acquisition cost becomes a profit opportunity. The larger the spread, the more attractive the opportunity. This is not a theory unique to tobacco. It applies to alcohol prohibition, fuel smuggling, pharmaceuticals, and countless other heavily taxed or restricted goods.

The argument that “criminals cause illicit trade, not taxes” is technically correct but economically incomplete. Criminal actors supply the product. Tax policy determines how lucrative supplying that product becomes.

Consider the causal chain in its simplest form. The government increases excise sharply. Retail prices rise accordingly. A portion of consumers quit. Another portion reduces consumption. But a remaining segment of lower-income, price-sensitive smokers still seeks supply. At the same time, the price gap between legal and illegal products widens dramatically. That widened gap increases potential profit margins. Entrepreneurs, legal or illegal, respond to profit margins. Supply shifts to meet the persistent demand.

To say there is “no evidence” of causation is to ignore this structural logic.

Of course, correlation alone does not always prove causation. Social phenomena are complex. Enforcement capacity, border control, corruption, geographic position, and organised crime networks all matter. But when the same pattern appears across multiple jurisdictions with vastly different cultures and enforcement regimes, high taxes accompanied by significant illicit incentives, the repetition strengthens the inference.

In countries with moderate tax differentials, illicit trade exists but is often manageable. In countries with extreme price gaps, illicit trade becomes entrenched. The size of the arbitrage opportunity matters. The scale of the incentive matters.

None of this means tobacco taxes are pointless. Price is one of the most effective tools for reducing consumption, particularly among young people. Many smokers quit because of cost pressure. That effect is real.

But policy tools operate on gradients, not absolutes. Push the lever too far, too fast, and secondary effects intensify. When those secondary effects include organised crime expansion, loss of regulatory control over product standards, and erosion of tax revenue, a serious evaluation becomes necessary.

There is also an equity dimension rarely discussed. High tobacco taxes are regressive. They disproportionately affect lower-income smokers. When legal prices exceed what that group can afford, illicit markets become not just attractive but rational. In that sense, the black market is not merely a criminal phenomenon; it is also a price response.

Public health debates often frame tax increases as an unqualified good and criticism as industry-aligned obstruction. But mature policy analysis should be capable of acknowledging trade-offs. If a strategy produces both measurable reductions in legal consumption and measurable expansion of illicit supply, both outcomes must be weighed.

It is entirely possible and likely that higher taxes reduce smoking for some while simultaneously increasing illicit sourcing for others.

The uncomfortable truth is that in heavily taxed FCTC signatory countries with persistent black markets, the relationship is not random noise. It is not an inexplicable coincidence. It is the predictable interaction of price, demand, and profit.

Correlation does not always equal causation.

But when the mechanism is clear, the incentives are obvious, and the pattern repeats across jurisdictions, denying causation begins to look less like scientific caution and more like institutional defensiveness.

In this case, the economic logic is not subtle.

It is cause and effect.

And sometimes, correlation does equal causation.