The phrase "a fraction of average" is correct and usable in written English.
It can be used when discussing a portion or a small part of an average value in a statistical or mathematical context.
Example: "The results showed that the performance of the students was only a fraction of average, indicating a need for improvement."
Alternatives: "a portion of the average" or "a small part of the average".
The units are 38,000 square feet on average — a fraction of the average 182,000-square-foot Wal-Mart supercenter.
Growth is now at its slowest pace in a decade at about 5%, and that isn't enough to significantly lift average annual incomes of only $1,500, which is a fraction of the average $10,000 for emerging economies.
Gradual separation has two parameters, M and S. S is the average time between initial divergence and complete separation, as a fraction of the average species lifetime (typically 0≤ S≤1).
Those customers, who can also store shows on a cloud-based DVR, pay $8-12 8-12month, a fraction of the average cable TV bill, for the service.
A movement tries to convince Americans to buy homes that are a fraction of the average size.
Commuters have given up hope in their train operators, according to the passenger watchdog, as official figures showed Southern received a fraction of the average complaints despite having the most cancellations and late-running services.
The economies of the Middle East and North Africa have been weak for years, and per capita growth over the past three decades was only half a percent, a fraction of the average for emerging economies, according to the International Monetary Fund.
Aereo picks up the signals of free-to-air channels and streams them to its subscribers over the internet, so they can watch them with the same good picture quality as they get via cable, but for a fraction of the average monthly cable bill.
The value of std represents a fraction of the average channel value.
where is a uniformly distributed random variable, is a factor controlling the maximum perturbation allowed as a fraction of the average period.
