A note with a 70% participation rate on an index that rises 20% pays 14%. A note with 150% participation pays 30%, but the higher rate is always funded by something else, typically a cap on maximum return, a longer term, or exposure to a barrier on the downside.
Compare the whole payoff rather than the participation figure alone. A 150% rate with a 25% cap on a five-year note delivers less than a 100% rate with no cap in a strong market, and the two are often marketed side by side.
Participation is normally calculated on price return, excluding dividends. On an index yielding 2%, five years of foregone dividends is roughly 10% of return that never reaches the investor. See principal-protected-note.
Related: principal-protected-note, structured-product, autocallable-note, total-return, barrier-option, issuer-credit-risk