Where the words come from
Positive externalities as beneficial spillovers, private against social benefits, the flu-shot market with MPB, MPC and MSB, under-production, the subsidy equal to MSB minus MPB, and the examples of research copied by rivals and restored homes raising neighbouring property values; the positive externalities of education — Principles of Economics 2e, OpenStax, licensed CC BY 4.0. https://openstax.org/books/principles-economics-2e/pages/13-1-why-the-private-sector-underinvests-in-innovation. Changes: "flu shots" to "flu jabs"; Q Market, Q Social, P Market and P Social relabelled Q1, Q2, P1 and P2; D Market and D Social named MPB and MSB throughout; the welfare-loss triangle described by us; the measles, pizza and beekeeper examples invented; the education externalities condensed from 2e's list (better health, lower crime); British spelling; the education externalities attributed to Walter McMahon as 2e attributes them; the external benefit card's definition is ours, built on 2e's "beneficial spillovers to a third party" and framed as the gap between MSB and MPB so that it does not restate the definition box.
The question and the page layout are our own.