By adding a decoy product to the mix, you help your consumers rule out the lesser quality, same-price value product for the high-quality, same-price value product, making the choice a no-brainer.

Probability and Frequency.
Frequency gives the prevalence of an occurrence whereas probability gives a statistical percentage. In dealing with probabilities and frequencies, we can relate to data best when we say “1 out of 10” rather than use a percentage. People just cannot fully relate to a “0.1” statistic.
It’s because we can relate to the whole 1 in the 1 out of 10 (and we neglect the 10 — it’s called denominator neglect funnily enough). But we don’t have a sense of a “0.1 of something”. It’s not a real-world concept.