Is there an answer based on fractions or percentages?

What papers set out the raw data?

Cheng, T.-P. Relativity, Gravitation and Cosmology, Second Edition 2010 Oxford U. Press: Oxford at p. 259 states, in reference to the 1998 papers: “They made the astonishing discovery that the expoansion of the unieverse was actually accelerating, as indicated by the fact that the measured luminosities were on the average 25% less than anticipated ....”.

The abstract for Riess, A. G. / others Observational evidence from supernovae for an accelerating universe and a cosmological constant 1998 Astron. J. , Vol. 116 p. 1009 states: “The distances of the high-redshift SNe Ia are, on average, 10% - 15% farther than expected in a low mass density Omega (M = 0.2)0.2) universe without a cosmological constant..”

What articles and what statements, observations, and data in those articles are the basis for Professor Cheng’s assertion?