16.5
Externalités Positives
Les externalités positives se produisent lorsque les agissements d'un individu ou d'une entreprise prenant part à une transaction commerciale avantage…
Les externalités positives se produisent lorsqu’un tiers bénéficie d’une transaction économique sans être directement impliqué.
Prenons l’exemple des vaccins. Lorsqu’une personne est vaccinée, non seulement elle développe une immunité, mais elle contribue également à réduire sa transmission au sein de la communauté.
Sur le marché, les vaccins sont fournis à une quantité où l’avantage marginal privé est égal au coût marginal privé. C’est là que la courbe d’offre, qui représente le coût marginal privé, croise la courbe de demande, qui reflète le bénéfice marginal privé.
Cependant, cette quantité de marché ne tient pas compte des avantages externes pour la communauté, qui comprennent une réduction des coûts des soins de santé et une main-d'œuvre en meilleure santé.
La courbe de demande sociale reflète à la fois l’avantage marginal privé et l’avantage marginal externe. La quantité et le prix socialement optimaux des vaccins sont plus élevés que ce que le marché fournirait.
Ce triangle représente la perte sèche, c’est-à-dire la perte de bien-être social due à la sous-fourniture de vaccins. La société gagnerait à augmenter la production de vaccins jusqu’au point où la demande sociale croise la courbe d’offre.
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Q1: What is a positive externality and how does it differ from a market transaction?
A positive externality occurs when third parties benefit from an economic transaction without being directly involved. Unlike standard market exchanges between buyer and seller, positive externalities create unintended benefits for others. For example, when individuals pursue education, they gain personal skills while society benefits from an educated workforce that increases productivity and innovation across the economy.
Q2: Why does the market provide fewer vaccines than society needs?
Markets provide vaccines where private marginal benefit equals private marginal cost, ignoring external benefits like reduced disease transmission and lower healthcare costs. The private demand curve reflects only individual benefits, not community-wide advantages. The socially optimal quantity occurs where the social demand curve, which includes both private and external benefits, intersects the supply curve—a higher quantity than the market equilibrium.
Q3: What does deadweight loss represent in the context of positive externalities?
Deadweight loss is the loss of social welfare resulting from under-provision of goods with positive externalities. It represents the gap between market equilibrium quantity and socially optimal quantity. This triangle on supply-demand graphs shows the forgone societal benefits when production stops below the optimal level where external benefits are fully accounted for.
Q4: How do public transportation and vaccinations exemplify positive externalities?
Public transportation reduces traffic congestion and pollution, benefiting non-users through cleaner air and less gridlock. Vaccinations reduce disease spread, creating healthier communities beyond vaccinated individuals. Both generate external benefits—unintended positive effects on third parties outside the market exchange—that markets alone fail to capture or incentivize adequately.
Q5: What is the relationship between the social demand curve and socially optimal quantity?
The social demand curve combines private marginal benefit and external marginal benefit, reflecting total value to society. The socially optimal quantity occurs where this social demand curve intersects the supply curve. This intersection point represents the efficient level of production that maximizes total social welfare, typically higher than the market-determined quantity.
Q6: How can policy interventions address the under-provision of goods with positive externalities?
Policy can use price mechanisms like subsidies to lower costs and encourage consumption, or quantity-based approaches to mandate higher production levels. These interventions shift market outcomes toward the socially optimal quantity. Understanding price versus quantity-based interventions helps policymakers choose appropriate tools to correct market failures caused by positive externalities.
Q7: Why does education create positive externalities beyond individual earnings?
Education benefits individuals through increased future earnings and personal knowledge, but also generates external benefits for society. An educated workforce drives economic productivity, technological innovation, and civic engagement. These spillover effects—improved societal outcomes not captured in individual market transactions—represent the positive externalities that justify public investment in education beyond what markets alone would provide.