EDWARD JACKSON,1 in his "Norms of Refraction," stated: Norm is defined as: "A rule or authoritative standard: a model, a typical example." In the same article, Dr. Jackson stated:
Norms of refraction are so important that they have been assumed or accepted on the observance of a few eyes. But they will be exact and useful only when the averages and changes have been noted for a great many. The records of a large city clinic, or the facilities of a university laboratory are worth very little in seeking such norms. They must represent the result of a large number of clinical observations made with care by established methods, over long periods. The return of clinic patients is so uncertain and irregular that very little can be learned from them in such an investigation.
Jackson also suggested:
The average spherical refraction be considered as an average of the refraction
SLATAPER FJ. AGE NORMS OF REFRACTION AND VISION. Arch Ophthalmol. 1950;43(3):466-481. doi:10.1001/archopht.1950.00910010475007