Fischer Black (1938-1995) and Myron Scholes (b. 1941), who in 1973 developed the Options Pricing Model that bears their names, had published a paper in 1971 that determined that a first class airline ticket should cost no more than 44 percent above the price of an economy ticket for it to be worth the price. They published an update in 1991 in which they said the percentage was still valid.