The phrase "how much extent" is not correct in standard written English.
It is typically used incorrectly as "extent" already implies a measure or degree, making "how much" redundant.
Example: "I am curious about the extent of the damage caused by the storm."
Alternatives: "to what degree" or "how far".
At present, 31 women per 10,000 screened have an interval breast cancer diagnosed after negative mammography.61 It is likely that supplementary ultrasound could help decrease this risk by detecting cancers already at screening, but it is not yet clear by how much because the extent of overdiagnosis for now remains uncertain.
Yet later in the book he describes, to a soul-baring extent, how much he loves his fiancée.
The Soviets had learned, to a frightening extent, how much the availability of food allows civilization to occur.
So I can decide, to a certain extent, how much I want to be in the middle of combat.
Facebook users can control to an extent how much information they give the company about their location.
Facebook, however, does let you fine-tune who can see your "likes" and pictures, and, to a lesser extent, how much of yourself to expose to marketers.
But it also opens up the question of how much and to what extent companies can move their annual meetings forward.
Experiencing a commute in the D.C. region without a working Metro system revealed two drastically different experiences, much of it depending on what people did for a living and, to some extent, how much money they make.
But I think there are lots of legitimate questions about its extent, how much humans are causing it, and certainly there is a very real and necessary debate about the mechanism for dealing with it".
"It's going to lower the amount of money in the system, but the question is, by how much, and to what extent, will the money find its way to other spots," said Jeff Buley, counsel to New York's Republican State Committee.
